Do stop/start systems lead to increased bearing wear?

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You may have heard the saying the 90% of engine wear occurs during starting, and so you might be worried that stop/start systems, which are a gas-saving feature for modern cars, might be detrimental to long engine life.
The 90% figure is based on the concept that the crank and cam bearings are hydrodynamic, which means they have almost zero wear rate when they are supplied with oil. This is because in hydrodynamic lubrication, the surfaces are separated by a thin film of oil and do not touch or wear against each other. When an engine starts up, it can take a few seconds for pressurized oil to reach all of the bearings, if the engine has been off for a few hours, or just about 1 second if the engine has been recently run. So, yes theoretically bearing wear is not insignificant during a start-up, but the fact that the bearing surfaces are still wet with oil saves them from any significant wear. Another way of looking at this is that 90% of virtually no wear is still virtually nothing.
In spite of this not really being an issue for stop/start engines, the car companies have switched the top layer of crank and rod bearings to low-friction teflon-like materials to further make this a non-issue.

• This topic was modified 5 years, 6 months ago by admin.

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