Quote:
Originally Posted by MikeGMT
Just for curiosity's sake. The transmission for cars with stop/start have a oil pump to maintain the correct hydraulic pressure to keep the first gear in standby mode ready to pressurise the clutches at start up. Similarly Twin Engine variants have a pump to provide lubrication when in electric drive with the engine stopped.
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With plain bearings such as the crank journals or big ends, it's not oil pressure per se that prevents metal on metal contact, the relative movement of the surfaces builds up a hydrodynamic wedge of fluid - once that wedge is built, in theory, you could replace the engine oil with water and have no loss of "lubrication" (until it boils!) - the oil pump simply has to provide enough fluid to cover losses from the oil (or water!) being flung out the bearing. I've absolutely no doubt that stop start reduces engine life - whether that's enough to reduce it to less than the life of the rest of the car is open to debate. Obviously startup is where the oil earns its stripes.