Category Archives: Engine Management

WATER PUMP REPLACEMENT: THE DO’S AND DON’TS

Water Pump Replacement: The Do’s and Don’ts

Replacing a water pump requires a fair amount of technical expertise. Are you planning on installing a new water pump? These do’s and don’ts will help you avoid 9 common mistakes.

1. Don’t Worry if the New Water Pump Looks a Little Different from the Old One

It is possible that there’s a visual difference between the new water pump you’re about to install and the old pump you have just removed. Perhaps the new one has a metal paddle wheel while the old one had a plastic paddle wheel, or perhaps its shape is somewhat different. Don’t worry about these minor differences; all that matters is the position of the water pump pulley. It should be at the same height as in the old pump because – if the belt starts rubbing against the pulley – it will become frayed. To check if you’re good to go, simply put both water pumps on your workbench, face down (i.e. with the side that touches the engine), and compare the position of the pulley.

2. Do Flush the Cooling System

Not flushing the cooling system is a common mistake that could cost you dearly. After all, the old coolant is likely to be contaminated, and its impurities could settle where the dynamic seal is supposed to form. As a result, these impurities will cause scratches on the dynamic seal surface, which could, in turn, lead to premature pump failure. To remove all the debris from the cooling system, flushing is key. A hose and a standard cleansing agent might do, but using a flush tool like the Gates Power Clean Flush tool will help you to do the job properly. Tip: if you flush the cooling system with a water pump attached, use the old water pump and not the new one, to prevent impurities from contaminating the new pump.

3. Don’t Apply Sealant to an O-Ring or a Dry Seal

When changing a water pump, replace all old gaskets and seals with new ones. If your new  pump comes with a seal, make sure it’s in impeccable condition before installing it. (Some seals are so thin you could easily damage them when you rip off the packaging.) Perhaps you’re tempted to apply sealant to an O-ring or a dry seal, just to be ‘extra safe’, but these seals don’t need sealant! If your rubber ring won’t stay put, just use a drop of coolant or oil instead.

Only apply sealant if the vehicle manufacturer recommends it, and don’t use too much of it. Put a thin, even bead along the edge and wipe off the excess before mounting the water pump. If you do this after you’ve mounted the water pump, you won’t be able to see the excess sealant on the inside, where it will damage the cooling system. The sealant will clump together into chunks that contaminate the coolant and can cause leakage or do terrible damage to the thermostat.

Only apply sealant if the vehicle manufacturer recommends it, and when sealant is prescribed, be sure to use in the correct way.

4. Don’t Use Coolant That’s Old or Too Cold

Collecting the coolant from your old water pump and reusing it may seem like a sensible (and economical) thing to do, but we strongly advise against it. After all, coolant tends to deteriorate: it has an expiry date. Refill the cooling system with new coolant and make sure …

  • … to use the kind recommended by the vehicle manufacturer (don’t start mixing coolants either, because they might counteract each other).
  • … to get the proportions right. If you add too little antifreeze, your cooling system is more likely to freeze, but adding too much might also be harmful. We recommend a fifty-fifty mix of water and antifreeze (make that 65% antifreeze and 35% water for Alpine-cold or Siberian climates).
  • … to mix in warm water with your antifreeze – as odd as that may sound. Adding cold coolant to a heated engine can cause thermal shock and damage the seal, even in a new water pump.
  • … to use distilled, deionized or even bottled water, but never tap water. Regular tap water can be very hard, leaving mineral deposits inside the radiator, heater core and engine block. When these deposits break off, they can damage the water pump seal.

5. Do Rotate the Pump Manually

A lot of mechanics stick to the following procedure: replace the water pump, tighten the bolts, install the belt, tighten the tensioner, refill the cooling system … and start the engine (or just rev it up). But coolant takes a little time to get everywhere it’s supposed to be, so the water pump runs dry for a few seconds. This ruins the seal and heightens the risk of premature leaks or a noisy water pump. Instead we’d advise you to ease the car down after you’ve installed a new water pump, refill the cooling system, lift the car back up and manually rotate the pump about ten times, all the while making sure it rotates freely. Due to this rotating movement, coolant gets sucked into the mechanical seal component, effectively creating a film, which keeps coolant from spilling out.

6. Don’t Worry About Seepage from the Weep Hole

Every mechanically driven water pump has a weep hole that might leak a little in the beginning. Some seepage from the weep hole is completely normal with a new water pump: a mechanical seal has a break-in period of about ten minutes (meaning that it takes about ten minutes of operation for the seal to properly seal itself). However, if you still see seepage a few days after you’ve replaced the pump, or if you notice more pronounced seepage or even drips from the weep hole, you do have a problem: these symptoms point to a faulty installation.

7. Do Properly Vent the Cooling System

When you’re done replacing a water pump, it’s good practice to burp the cooling system to get rid of all the trapped air. Some thermostats have a small hole at 12 o’clock, and a jiggle pin which allows the air to escape (while preventing new air from getting in).

8. Do Change the Water Pump, Belt and Other Drive Components at the Same Time

It is crucial to inspect the belt drive system that is driving the water pump, while you’re at it. A bad belt and tensioner cause premature bearing and shaft failure and drastically reduce pump life. Conversely, a leaking water pump inevitably affects the belt and tensioner. That’s why we recommend changing the water pump, belt and other drive components all at the same time. Our timing belt kits and accessory belt kits include water pumps or even water pumps and thermostats.

9. Do Change the Coolant Every Five Years

Coolant contains anti-rust agents, corrosion inhibitors and lubricants for the water pump, yet these components deteriorate over time. Our rule of thumb: change the coolant every five years to preclude cavitation problems. After all, coolant tends to become more acidic over time, increasing the risk of cavitation – a bizarre phenomenon in which what seem like tiny ‘air bubbles’ pop and damage the paddle wheel and other components. (These ‘air bubbles’ actually contain super-hot vapour that can crack plastic and erode metal if it implodes). You cannot see the cavitation bubbles, but engine overheating and weep hole leaks are tell-tale signs.

What Causes Early Pump Failure?

Following recent analysis of our inspection data we’ve been able to identify the most common causes of premature water pump failure in passenger cars throughout Europe. Interestingly, the most frequently recurring issues are as a result of installer error, mainly due to:

  • Dry rotation/testing for free movement of water pump assemblies before installation
  • Use of inappropriate seals/gaskets or sealant;
  • Incompatible/contaminated coolant;
  • Installation of worn/defective parts.

puc2

Although these are major causes, they’re not listed in order of importance and all are regularly repeated somewhere in one of our European markets on a daily basis. They all, however, can be avoided through training, access to good technical information, following the correct procedures and using the appropriate tools.

Understanding what makes water pumps fail is the key to longer operational life of the drive system and its individual components and that’s why Gates gathers so much inspection data.

It’s important to understand that the average water pump has a throughput of around 1.7 million litres of coolant over a four year (100,000 kms/60,000 miles) duty cycle. Routine replacement of the water
pump without investigating the cause of failure could condemn the new replacement to an even shorter life.

Fewer remedial repairs, more workshop efficiency and increased levels of customer satisfaction must be the goals of every workshop manager, so access to reliable technical information is essential.

The GatesTechZone

www.GatesTechZone.com is an important resource for any drive system specialist. It includes product support, technical tips, details about tools, installation and diagnostic procedures, as well as access to the Gates online catalogue. It also identifies the most common causes of failure and explains how errors can be avoided.

DRY ROTATION/TESTING THE WATER PUMP

As well as helping to keep the engine cool, the coolant plays an important role in maintaining an efficient seal inside the water pump. Constant lubrication of internal seals is essential.

Never dry rotate/test for free movement of a water pump assembly before installation – even for a few seconds. Dry rotation can permanently damage the internal seals and that will cause a leak. After the system has been refilled with coolant, you should rotate the drive pulley by hand a few times. This will allow a small amount of coolant to lubricate the mechanical seal before the engine is started.

Tip: To test for free movement of the water pump assembly before installation, fill a reservoir full of coolant and immerse the water pump. A test for free movement can now be made without fear of compromising the integrity of the water pump!

USE OF INAPPROPRIATE SEALS/GASKETS

Old gaskets and seals must be replaced. If the water pump has a gasket or seal, never apply sealant as this will cause component failure. Use sealant only when specified by the manufacturer. Improper use can cause problems with water pump seating or the seal can be compromisedIf Sealant is recommended, put an even bead along the edge and around the coolant passages (installation holes) on the impeller-side of the pump. Too much sealant will compromise the installation because it breaks off and contaminates the coolant.4

Tip: Different sealants have different drying rates. Always respect the instructions of both the sealant manufacturer and the water pump manufacturer.

UNSUITABLE/CONTAMINATED COOLANT

Use of unspecified or contaminated coolants leads to premature failure of the water pump. An unspecified, incompatible or mixture of different coolants usually leads to insufficient protection against rust or corrosion.

Contamination commonly occurs in systems that haven’t been properly maintained.Abrasive particles circulate through the system, scratching and damaging the seals and internal surfaces, destroying the individual component and creating the pathways that allow leaks to develop.Before installing a new water pump, drain and flush the entire cooling system with appropriate equipment.
5

Tip: Modern cooling systems are complex, contain a range of different materials and rely on specific coolant formulations for protection from rust and corrosion. This is the key reason for the growth of manufacturer-approved coolants. Always use the recommended specification.

INSTALLATION OF WORN/DEFECTIVE PARTS

A worn belt fitted with a new water pump, or a new belt fitted with an old water pump, is a recipe for premature drive system failure. Gates recommends a complete drive system overhaul – replacing the belt and the tensioner(s) at the same time as the water pump – by means of an all-in-one kit. This minimises risk of drive system failure and optimises the lifetime of the individual components.

Tip: Follow the recommended water pump installation procedure and the kit manufacturer’s  recommendations with respect to belt tensioning and torque setting.

AND FINALLY…3

Seepage from the weep hole in a newly installed water pump is normal during the initial ‘break-in’ period – there is no cause for concern. Once the mechanical seal has seated itself, the seepage will stop. Prolonged seepage or a large coolant bleed mark around the weep hole is abnormal and indicates impending water pump failure.

By performing a drive system overhaul and following the manufacturer’s fitting instructions every time, installers can ensure a further 100,000 km/60,000 miles of drive system reliability.

Glow Plug Tips and Tricks

Glow Plug Tips and Tricks

POWERCLEAN Flush Tool Backflow Prevention – A Technical Tip from Gates

A Backflow Preventer (BP) is a required component of the POWERCLEAN Flush Tool which is used to safely discharge back pressure. This is done to protect the water supply system piping from potential pressure damage as well to the potable (drinking) water from potential contamination. BPs have become a building code standard in many areas today but since there is no guarantee a BP exists at every location where this tool may be used; a BP has been included with every tool kit.

  • The BP must be used to protect the water supply system.
  • The BP should be used at the spigot end of the water supply hose.
  • The BP will discharge water (backpressure); this is normal operation.
  • Excessive discharge from BP indicates air pressure set too high.

screen-shot-2016-11-03-at-14-30-28Problem:
Regardless of what pictures and/or videos you may have seen, the
BP is not intended for use at the gun end of the water supply hose. Unfortunately, this is a common problem and may cause “trouser soaking”. This is not a design flaw, “leak”, or an inherent problem with the tool; it is just a simple set up error.

Solution:

Move the BP to the spigot end of the water supply hose.

 

 

Problem:

When connecting the air supply line there is an immediate and large amount of discharged water from the BP. This is generally a result of the air pressure set too high.

Solution:

Point the tool in a safe direction and pull the trigger; while operating and observing the pulse, reduce the air regulator pressure until the pulse begins to weaken. Then increase the regulator pressure only to return to a strong pulse, no higher. When releasing the trigger, the BP discharge will now be much less (considered normal).

    • The Powerclean Flush Tool is not a pressure blaster. More air pressure is not better. This tool is converting the pressure energy into kinetic pulse intensity also known as velocity-energy.
    •  The air “ON-OFF” function and the primary method to limit BP discharge is to: (1) only connect the air line when ready to actually pull the trigger and work with the tool and then (2) immediately disconnect the air line when not working with the tool.

Problem:

Unique situations create issues with the BP being used at the spigot end of the water supply hose; such as indoor water connection and adjoining machinery.

Solution:

In such a case we can only recommend to wrap a rag around it, put a bucket under it, or find another creative way to control the “spray” and/or capture the outflow. The BP must always be used.

What’s driving water pump replacement?

Andrew Vaux, Training & Support Team, Gates UK offers his trio of drive systems technical tips.

Problems when the pump is up front

While all of the technicians at a recent Technical Workshop subscribed to the notion that belt kits should be fitted to all drive systems, some views implied that the Auxiliary Belt Drive System (ABDS), or front end drive, was considered to be of less critical concern than the timing belt drive. ABDS drives have become more complex and the number of drive system components has increased in recent years. For example, Torsional Vibration Dampers (TVD) and Overrunning Alternator Pulleys (OAPs) have been introduced to protect the multi-ribbed belt by absorbing vibrations and managing the various stresses and strains imposed by today’s high performance engines.

As such, these components are subject to wear and, in common with the belt, their overall performances decline with age. In addition to the alternator, key safety and comfort systems – power steering and the air conditioning – draw their power from the ABDS. Increasingly, it may also drive the water pump. This is true for about half of the vehicles on the market and especially so on a wide range of popular models, such as the Mercedes A150 1.5 (Petrol), Volkswagen Golf 1.4 (Petrol) and BMW 118d 2.0 (Diesel). Vauxhall/Opel and Renault are among many other manufacturers with similar drive system designs.

What's driving water pump replacement?Premature failure

An unexpected ABDS failure can have serious consequences – such as overheating of the engine or the sudden loss of power steering at a crucial time. There is also the very real possibility that debris generated in the destruction of the auxiliary belt might come loose and contaminate the timing belt drive. Those attending this particular Workshop heard that on a recent inspection, broken parts from the tensioner travelling at high speed had penetrated the timing belt cover, with devastating consequences for the engine. A more casual approach to ABDS maintenance can lead to catastrophic results. The inevitable conclusion is that issues with any one of the components in the ABDS very soon become issues for them all. Furthermore, it’s folly to expect a new component to integrate smoothly with a host of others that have been operating in tandem for the same amount of time as the part(s) about to be replaced. The beauty of an ABDS kit is that, if chosen carefully, it includes all of the parts required to overhaul the drive. Since the end of February a kit from the Micro-V® Kits with Water Pump range from Gates also includes the appropriate water pump for each application.

So if installing a belt kit makes sense, replacing the water pump is an absolute must in any drive belt drive system, especially for garages keen to avoid early comebacks. In the event of a complaint, the service provided by the garage will be measured against ‘good engineering practice’, which demands that all of the components in the ABDS should be replaced at the same time. Furthermore, ABDS kits that include a water pump give added value and protection for both the garage and the customer. The warranty for all of the parts is with the same supplier.

Water pump inspection checks

On inspection, a number of indicators may confirm a more urgent reason to change the water pump. These include:

  • Bleed marks around the weep hole, on the mounting surface or around the housing
  • Rust and corrosion on the pump surface and impeller fins
  • Cavitation – pock marks, play in the bearing
  • Evidence of bent or broken shaft

What's driving water pump replacement?

Reasons for premature failure include:

  • Poor installation
  • Contaminated/non compatible coolant
  • Improper use of sealant or gaskets
  • Bubbles in the coolant that burst under pressure – cavitation
  • Misaligned belt
  • Over-tensioned belt

VAG technical update

Changes to VAG 1.6 diesel CAYB & CAYC engines affect models equipped with air conditioning, from October 2009 onward. Classic multi-ribbed V-belts replace the earlier ‘elastic’ belts – a design that did not require a tensioner. For models from October 2009 onward, Gates recommends installation of belt 6PK1070, together with tensioner T38427.

Please note: the Gates range includes Stretch-Fit belts for all earlier applications that haven’t yet been adapted. Installation instructions and details about the correct tools required are printed on the inside sleeves and are also available from the online catalogue.

What's driving water pump replacement?

Quote me on that:

Water Pumps

According to ClickMechanic – the online job provision service for motor mechanics – water pump replacement tops the list of its most popular thermal management system job quotations. “With A/C category jobs we find that most people would prefer for the system to be checked and adjusted before they want a technician to actually embark on any repairs. After this, the most popular A/C jobs we see relate to servicing of the A/C condenser or compressor,” says ClickMechanic’s Kurt Schleier. “Taking into account the total number of quotes we give for each brand, we found that owners of high-end cars from brands like Mercedes-Benz and Jaguar are more likely to request these A/C jobs, with only Honda owners requesting more quotes,” he adds.

Water pump popularity Kurt continues: “As the heating and cooling systems on cars are usually inextricably linked, issues with thermal management can be complex. Interestingly, our most popular thermal management job is not an inspection, but rather a water pump replacement. This could suggest customers are confident of the exact issue on their cars and the need for replacements. “In all likelihood it means they will already have had their overheating problem checked, for example during a breakdown recovery of their car. There is also a clear seasonal aspect. In January, for example, car owners are far more likely to request quotes for heaterblower motors and heater matrix issues than in any other month.”

Zirconia switching Lambda sensor – function and operation

There are basically three different, non-interchangeable types of Lambda sensor. The zirconium dioxide and titanium dioxide Lambda sensors are also called switching, voltage jump or ‘binary’ sensors, because their output signal varies back and forth between two values, depending on whether the fuelling is in a rich or lean state. The third type is the broadband Lambda sensor.

Method of operation of the zirconium dioxide sensor
This sensor element has a hollow, thimble shaped design. The inside surface is in contact with ambient air. The outside surface is situated such that it lies in the stream of the exhaust gas. Both surfaces are covered with a thin, porous platinum layer which acts as electrodes.

There will always be a difference in the concentration of oxygen between the exhaust gas and ambient air. When the Lambda sensor reaches operating temperature, oxygen ions start to move through the ceramic electrolyte from the side that has a greater concentration of oxygen towards the side that has a lower oxygen concentration, attempting to reach a state of equilibrium.

As these ions leave one platinum layer and reach the other layer, a potential differential results, giving rise to an electrical voltage. If the mixture is lean, the voltage will be relatively low (approx. 0.1 volts). If the mixture is rich, it will be relatively high (approx 0.9 volts). There is a large characteristic voltage jump as the stoichiometric point (Lambda = 1.0) is passed.

Testing zirconia switching Lambda sensors
Testing with an oscilloscope is the most effective method. It shows minimum and maximum voltage, the response time and the frequency. When performing the test, the manufacturer’s specifications must be observed.

Test procedure
1. Bring the engine to operating temperature at 2,000 rev/min.
2. Connect the oscilloscope to a signal line without disconnecting the sensor from the engine control unit.
3. Set the measurement range to 1-5 volts and time to 5-10 seconds (observe manufacturer’s specifications).
4. If applicable, activate automatic signal recognition. A correctly functioning sensor swings between 0.1 and 0.9 volts with a frequency of 0.5-4 Hz.

Diagnosis tips
A visual inspection often provides the initial clues for a possible malfunction. Inspection points for the workshop are:

Resistance value of the heating element
If it is above 30 ohms then the sensor is defective.

Cables
Are they broken or is the plug broken? Is the cable seal intact? Has moisture penetrated into the plug? Are the plug contacts in good condition? Is the cable routing too tight?

Sensor body
Does the sensor show any visible damage?

Make sure you use the right sensor type
Each vehicle will have a specifically designed sensor type and therefore it is essential that they are only replaced with matching specification sensors. You can use the current NGK/NTK catalogues to identify the correct replacement sensor for each application.

‘Broadband’ Lambda sensor – function and role

With the ever greater demand to reduce fuel consumption and to lower exhaust emission levels, it has become necessary to operate engines away from the stoichiometric fuelling point under certain conditions. An enriched air/fuel mixture (Lambda less than 1.0) may be required during a cold start and under full load conditions.

These modes of engine operation are subject to continuous research into new strategies to reduce fuel consumption. Some more recent engine concepts are designed to work at an air/fuel ratio much leaner than stoichiometric, at least for part of their operation. These ‘lean burn’ engine strategies must be strictly and accurately controlled.

For this purpose, ‘broadband’ oxygen sensors were developed. These sensors can accurately measure and produce an output signal which is proportional to a very wide range of air-fuel ratios. Fuelling can be maintained at any required air/fuel ratio and their operation is both extremely fast and accurate.

Broadband sensors are also used in modern diesel engines, which mostly operate with an excess air factor.

Method of operation
Broadband sensors consist of two cells: one measurement cell and one pump cell. With the help of the measurement cell, the oxygen concentration of the exhaust gas – which flows into the detection chamber – is measured and compared with that of a stoichiometric mixture.

As a stoichiometric value would generate a 450 mV output any deviation will cause the pump cell to transport oxygen ions into or, by reversing the current, out of the detection chamber in an attempt to regain the target value of 450 mV. Measurement of the value and direction of flow of this generated pump current enables precise calculation of the air/fuel ratio. At a stoichiometric air/fuel ratio there is no net current flow, as the residual oxygen concentration within the detection chamber is designed to produce 450 mV at this value.

Signal output
If a stoichiometric mixture is present (Lambda = 1.0), no current flows through the pump cell. If a rich mixture is present there is very little residual oxygen. A negative current is produced at the pump cell and oxygen is pumped into the detection chamber.

If a lean mixture is present there is more residual oxygen and a positive current is produced at the pump cell. Oxygen is pumped out of the detection chamber.

Cable assignment
NTK broadband Lambda sensors have five cable connections. The yellow and blue cables provide the heater power control. The pump signal current flows through the white cable; the measurement cell signal flows through the grey cable. The black cable provides the earth connection for both pump and measurement cells.

Lambda sensors explored

Tim Howes, Deputy General Manager – Supply Chain & Technical Service, NGK Spark Plugs (UK), looks at the origins of vehicle Lambda sensors and the various types.

The term Lambda is used to designate the value of the ratio of the mass of air supplied to an engine divided by the theoretical ideal requirement. That sounds very grand but, essentially, it means that if the engine is supplied with a fuel rich mixture it would have a Lambda reading of less than 1.0 Lambda. Alternatively, if it was supplied with a fuel lean mixture it would produce a reading greater than 1.0 Lambda. In most cases the basic function of a Lambda sensor is to ensure that the fuelling system supplies the engine with a mixture as close to 1.0 Lambda as possible.

Why the need for a 1.0 Lambda mixture?

Most engines needs to be supplied with this 1.0 Lambda mixture because it is the ratio of fuel and air that produces the most complete combustion, thereby providing an efficient use of fuel. The resultant exhaust gases can be dealt with effectively by a three way catalytic converter. This theoretically ideal ratio is called a stoichiometric mixture and for a standard petrol engine the air/fuel ratio is 14.7:1 by mass.

Sensors achieve this control by measuring the residual oxygen content of the exhaust gas before it enters the catalyst; this is why Lambda sensors are also (and more correctly) known as exhaust gas oxygen sensors (EGO). An oxygen concentration outside certain limits will result in the sensor signalling the ECU to amend the fuelling system calibration, thus bringing the mixture back into acceptable limits.

Sensor variations

There are several different types of oxygen sensor in use but, for the majority of cars, there are two non-interchangeable sensor types, using a different strategy to detect the oxygen concentration in the exhaust gas.

Zirconia type

This is by far the most popular sensor type. Under the protective metal end cap there is a thimble shaped ceramic element made from sintered zirconium dioxide. This has two thin micro porous platinum layers added: one covering the inside and one covering the outside. These layers are the electrodes to which the signal wires are attached. On top of the outer layer a further porous ceramic layer is added (aluminium and magnesium oxide) which protects the platinum from dissociation and erosion by the hot exhaust gases. The whole package is then fitted into a metal shell, part of which is threaded to allow fitment to the exhaust system.

This element is inserted into a convenient part of the exhaust system up-stream of the catalyst. The heat energy imparted by the exhaust gases will raise the temperature of the sensor. When 300°C is reached the Zirconia ceramic has a special property in that it becomes ‘permeable’ and will allow oxygen ions to pass through it. The centre of the thimble shaped ceramic element is hollow. This is to allow a pocket of ambient air to act as a reference gas.

In theory a stoichiometric combustion gas will have no oxygen present, however, in practice, small levels of oxygen are present. In an attempt to maintain equilibrium, oxygen ions will migrate through the permeable ceramic and platinum layers. The movement of these ions causes a voltage to be generated. Put simply, the sensor behaves like a small battery with the Zirconia acting as the electrolyte. In this way the voltage output is relative to the oxygen concentration in the exhaust gas.

Lean air fuel mixtures result in relatively small amounts of ionic movement due to the oxygen rich environment of the exhaust gas, whereas rich mixtures are deficient in oxygen, resulting in larger ionic movement as the sensor tries to achieve equilibrium across the element.

Around the stoichiometric point (1.0 Lambda) there is an abrupt and dramatic change in oxygen concentration, producing a large differential between exhaust gas and the reference air. This in turn produces a relatively large change in voltage. This voltage is the signal which is sent to the fuelling control system, enabling an adjustment to bring the air/fuel ratio back into the acceptable window around 1.0 Lambda. There is a natural tendency for the fuel system to overshoot the desired window, therefore the voltage output cycles – fuel lean/fuel rich between a minimum and maximum value – nominally between 0.1 V ~ 0.9 V. This occurs with a frequency of 1~2 Hz. If a gas analysis is carried out the reading may fluctuate between 0.9 Lambda and 1.1 Lambda.

Because the sensor has to reach 300°C before it starts to function there is a period after start up which is not controlled by the Lambda sensor. To combat this it is desirable to install the sensor as near to the engine as is practical. Under certain conditions exhaust gas temperatures can drop sufficiently to impair the function of an unheated sensor. A solution to both problems is to use a heater inside the sensor which rapidly brings the ceramic up to temperature. Heated sensors (HEGO) are therefore particularly desirable when trying to reduce noxious gas emissions. Most contemporary engine control systems are designed to work with heated sensors.

Titania type

The less common Titania sensors have a similar appearance but work in a different way. They use a layered titanium dioxide ceramic element with its electrodes sandwiched in between. At a critical point around 1.0 Lambda the Titania ceramic possesses the property whereby its electrical resistance changes substantially. If a small voltage is applied (typically 5 V) by the vehicle’s control system this change in resistance can be used to adjust the fuelling, keeping the exhaust gases within the desired limits. These sensors do not need access to ambient reference air.

Titania sensors are more expensive to produce but reach operating temperature faster, reaction times are faster and they can be made physically smaller. The sensor’s ceramic element requires a high degree of protection. This is provided by the metal end cap which has specially designed holes to allow a good flow of exhaust gas whilst preventing impact damage, water splash and extremes of temperature. Total protection against leaded fuel and some other air borne compounds can’t be provided, however. These unfriendly compounds can poison the sensor, slowing or preventing its operation.

Special types

There are some systems that allow the engine to run on considerably leaner mixtures under certain conditions and these require a special type of oxygen sensor called a ‘wide band’ or ‘broad band’ sensor. These are much more complex in operation with very sophisticated control mechanisms.

In addition, most road vehicles also have a second sensor fitted after the catalyst. This functions in the same way but is used to monitor the effectiveness of the catalyst and is often referred to as the CMS (catalyst monitoring sensor) or diagnostic sensor; this usually plays little part in regulating the fuelling system but can, on some applications, detect catalyst ageing and allow calibration changes to accommodate.

Helping to prevent drive train noises

In the UK Schaeffler is renowned for its leading LuK clutch, INA tensioner and FAG wheel bearing brands, and the company always goes the extra mile to provide even better products for its customers. This was demonstrated by the efforts it made when building a new acoustic testing facility at its Technical Development Centre in Herzogenaurach, Germany.

A room within a room
A special feature of the facility is a ‘room-in-room concept’, where an entire room is spring-mounted inside a larger room so that it moves independently and can be completely isolated as it is decoupled from the oscillation of the rest of the building. Special bricks were imported from Sweden as the interior rooms had to be of particularly high density (at least 2,400 kg/m³). Unsurprisingly, it has been named ‘the wobble room’ by staff!

The company’s engineers in the Competence Acoustics Centre (part of the Technical Development team) investigate the origins of irritating noise using the latest state-of-the-art analytical methods to discover how noise is generated and what can be done to eliminate it at the beginning of development. As such, typical tasks include investigations of airborne sound and vibration behaviour in the vehicle drive train, as well as in the chassis and its components, such as ball screw drives and roll stabilisers.

In addition, engineers also examine plain bearings and rolling bearings of all types and designs that are used in applications such as production machinery, wind turbines, hydroelectric power plants, railway, medical technology and household applications.

Vehicle test stand: here vehicles up to the size of a delivery van can be examined from a noise technical point of view.

Hi-tech equipment
Equipped with state-of-the-art measurement and computer technology, three test rooms and the so-called ‘wobble room’ have been installed in a 180 square metre area.

CTO Prof. Dr. Peter Gutzmer said: “This is an audible and tangible further extension of expertise at Schaeffler. With the new Herzogenaurach acoustic centre, we have created ideal conditions to further optimise the globally networked development activities at Schaeffler and adapt to customer needs even better than before.”

Especially in the field of drive technology, customers are paying more and more attention to low friction coupled with the quiet operation of the individual system components, and this is also true for bearings in electric motors and devices for the home and office environments.

Acoustic issues from all areas of automotive and industrial engineering can also be addressed quickly and competently.

Dr. Arbogast Grunau, Senior Vice President Corporate R&D Competence and Service, said: “The expertise concentrated here is the result of long-standing experience in product and system development and it is continuously being developed further.

“We use our network of competence to spread our knowledge and experience throughout the world, with training and seminars being an important medium. In this way we make an important contribution to Schaeffler’s global alignment, true to our motto ‘Together we move the world’ – here with a particular focus on noise optimisation.”

Examination of airborne sound and vibration behaviour of car wheel bearings in an anechoic room

Reducing outside noise
The test rooms include a large acoustic vehicle test bay, a room for fatigue tests and one with extensive adaptation options. The ‘room-in-room concept’ covers 30-50 square metres of floor space with the largest room weighing more than 130 tons.

The interior ceilings and walls of the test rooms are lined with up to 35cm thick acoustic broadband compact absorbers to meet the sensitive metrological requirements of the acoustic staff.

Dr. Alfred Pecher, Manager, Testing Competence Centre Acoustics, said: “This constructional measure means it has also been possible to reduce noise intruding into the test rooms from outside – such as the sounds of trucks passing by – to a minimum, and to obtain technically accurate measurements.”

 Even large-size bearings weighing several tons can get inside the acoustic centre by means of a crane system, designed specifically for this purpose. They can also be examined there.

The importance of changing the water pump at the same time as the timing belt

Every mechanic wants to be able to diagnose vehicle problems with accuracy, but the dynamic nature of automotive design makes it difficult for even the most dedicated of experts. A recent technical workshop involving Gates highlighted degrees of uncertainty in connection with scheduled timing belt replacements and the installation of water pumps.

The Gates technical workshop programme is a modern way to keep abreast of drive system developments. These workshops are usually free to mechanics and organised by local motor factors in association with Gates, one of the world’s leading suppliers of timing belts and tensioners.

The uncertainties voiced at one such workshop in the north of Scotland related to:

  • Belt replacement schedules in synchronous belt drives (SBDS)
  • Belt ‘V’ kits
  • Rates of wear in the drive
  • Water pump replacement issues

The wide variety of differences in drive system layouts means that there is no standard procedure for installing every timing belt. What can be applied to every installation is good engineering practice.

During Gates’ technical workshops all over the UK, the company’s advice is to replace the metal parts at the same time as the belt by installing a timing belt kit. This recommendation is based on the knowledge that modern belt tension is high, that belt replacement intervals have increased and that components in the drive system are subject to variable amounts of wear.

While many garages agree, some attempt to save the customer money by installing just the belt. It is a risky strategy that could cost both the customer and the garage much more over the long term.

Change the pump
Another benefit of the Gates workshops is that mechanics are given a platform to discuss installation procedures with other drive system specialists. The question of the best time to replace a water pump was raised in the context of preventive maintenance.

Gates believes that a scheduled timing belt change is the best time to replace the water pump as much of the preparatory work and chargeable time has already been done. Some garages would rather not do so because the water pump seems fine.

Waiting for a water pump to develop a problem is risky and assumes the driver will notice it in good time, says Gates. Who to get the parts from The debate moved on to the choice of water pump. A few years ago, Gates introduced a water pump kit in response to installer demand. Mechanics wanted the kits because some water pumps and belts need to be matched (the company now supplies two different kits for some models). If they are not matched, there is a risk of premature drive system failure.

For example, the pulley profile might not match the belt that drives it. In such cases, the belt takes excessive strain and may shred. If the belt is blamed and replaced, the new belt will not resolve the problem. If a drive system failure does occur for any reason, the choice of a single supplier will involve the garage in one investigation procedure rather than two. This saves time and eliminates the chances of a dispute about the origin of the failure. In the meantime, the vehicle has to be repaired and the bill has to be settled.

In the event of a premature drive system failure, inspection of the parts is likely. Gates argues that, wherever possible, timing belts and water pumps should always be changed at the same time and that they should be sourced from the same supplier because of the degrees of assurance it provides.

Workshop responsibility
Although the mechanics in this particular workshop agreed that given a drive system’s susceptibility to wear and the need for specialist tools to maintain them, an overhaul of the complete SBDS makes sense, especially given the complex nature of some of the designs. However, they were unsure about their customer’s response.

Gates’ advice
Gates says that by replacing individual components, the responsibility of the mechanic is increased. For example, by replacing just the timing belt, a decision has been made that the tensioners and the water pump are good for another duty cycle. However, in the event of failure, the customer might be inclined to ask why the drive system was not subject to a complete overhaul.

With this in mind, it’s worth considering what preventive maintenance measures mechanics ought to be aware of in the Accessory Belt Drive System (ABDS), where there are many more components. The introduction of Overrunning Alternator Pulleys and Torsion Vibration Dampers, for example, means there are even more decisions to be made.

But perhaps that’s a subject for another debate.