Technical Information

Autochoice Car Sales – Technical Information

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DMF (dual mass Flywheel)

A dual mass flywheel is being increasingly fitted to newer cars especially diesel. Its designed to replace the normal flywheel and provide a smoother drive through to the gearbox/vehicle. It consists of 2 steel flywheels connected by 2 large springs which absorb torque form the crankshaft on each piston firing. The smoothness refines the drive but also enhances the life of the clutch and gearbox components as they are protected from the pulsing torque. Some offer a solid flywheel replacement, this is not recommended as it will ultimately increase the stress on other drive components. This is also the reason why a clutch should not be changed on its own as a worn DMF will cause the new clutch to fail prematurely. Please note the DMF can get noisey when it starts to wear, this is normal.

DPF (diesel particulate Filter)

These have been getting a lot of attention lately.. It’s all down to those Europeans in a drive to reduce emmissions further. The idea is that the filter acts as a storage devise for diesel soot. When it fills up it then burns it all in one go  (re-generate) and then it is ready to repeat this procedure again. The problem is that stop start driving only allows it to fill up as the car does not get hot enough to start the burn off procedure. This is why car manuals ask you to drive the car in a certain way (over 3200 rpm for 10 mins). This gives the car a chance to reach temperature and start the burn off. Another problem is that when it fills up too much the burn off cannot take place as the soot cannot get hot enough because there is too much of it to start with (the excessive soot acts as a coolant) so the DPF has to be replaced. Sometimes it can be just cleaned but be warned replacement is expensive. Prevention is better than cure….  Using the correct oil (low Ash) makes a huge difference. This oil is usually dearer than the normal fully synthetic 5/30 etc.. but be warned expensive oil does not mean it is the correct one. Low Ash or Low saps oil is specific to DPF cars and must be used for servicing and top ups. Low SAPS oils are specifically designed to be low in Sulphated Ash – a by-product of combustion that can cause the ‘mesh’ structure in a DPF to become irreversibly blocked. Such oils that are not low in Phosphorus and Sulphur can also have a significant, detrimental effect on Catalytic Converters – so the issue of getting the right engine oil is relevant to petrol and diesel vehicles alike.

One way to identify a Low SAPs oil is to look for an ACEA ‘C’ classification – C1, C2, C3 or C4 (It doesn’t necessarily follow that C1, is better or worst than C2, C3 or C4 – they are just different). ACEA (The European Automobile Manufacturers Association) sets standards for engine oils in Europe and its specification for Low SAPS oils begins with a ‘C’. However, most vehicle manufacturers have their own specifications for Low SAPS oils which can make the job of identifying the right oil for your vehicle quite complicated..So correct servicing is essential to keep the DPF alive. Should you want to remove the DPF this is now possible by way of a mechanical replacement and an ECU reflash to let the car know that it no longer has a DPF. The cost of this will be a lot less than a replacement DPF – ask the Autochoice service team for more information about dpf removal – a service which we now offer.

 

EGR Valve (Exhaust Gas Recirculation Valve)

The EGR works by re-circulating a portion of an engine’s exhaust gas back to the engine cylinders, which will in turn control emmissions. Because they circulate exhaust gases they are prone to carbon build up and so do clog up. Most modern engines now have exhaust gas recirculation to meet emissions standards. When they fail they will cause running problems and excessive fuel consumption. Some can be cleaned by removal other have to be replaced.

TurboChargers

A turbocharger is a mechanical item on the engine that is used to force more air down into the combustion process. This mean that more fuel can also be used and produce more power ­ In order to achieve this boost, the turbocharger uses the exhaust flow from the engine to spin a turbine, which in turn spins another intake turbine. The turbine in the turbocharger spins at speeds of up to 150,000 rotations per minute (rpm) — and since it is hooked up to the exhaust, the temperatures in the turbine are also very high.. So the turbo get very hot and is under huge amounts of stress. The engine oil stops it from seizing and it also cools the bearings in between the exhaust  and intake turbines, so must be good stuff. Turbo usually last 65-85k miles but can last twice that if the vehicle has been properly serviced.  Also be aware that other component failure (e.g. EGR valve) can cause excessive exhaust soot build up in the exhaust turbine which will eventually lead to seizure.

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