Quote:
Originally Posted by MartinK
Seems to be a much-discussed issue.
There's no suggestion that auto transmission wear is increased if the car is left in D (some people say that moving the selector constantly between N and D in stop-start traffic actually increases wear). However I would assume that because the viscous coupling is engaged and working when D and stationary, that it will increase temperatures, and hence "wear" the oil.
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That's what it said in my Mercedes Owner's Manual,
if stopped at traffic lights or for short periods do not move the shift out of D as this causes excessive wear but obviously if you are stuck in a traffic jam then better not to stay in D as the oil will get churned up but it should never get so hot it will
"wear the oil". To provide drive from the engine the oil in an automatic gearbox is continually sheared or cut this is a design feature of the oil it is specifically designed to take a lot of punishment, yes it will get hot but to cause the oil to deteriorate quickly you would need to tow a large load continuously. A lot of vehicles with auto boxes these days are sealed for life but what the manufacturers don't say is if the vehicle is used for towing or used in harsh conditions (excessive temperatures [hot or cold] or dusty conditions) then the oil should be changed more often. The oil in my Mercedes auto box was changed for the first time at 120,000 miles and it came out runny and dark red, the mechanic said
"you have a towbar but you don't tow a lot with this car do you?". He said if I had towed a lot it would have been thick and "gungy". After the oil change there was little difference in the gear change but there again it was a Mercedes and the auto box was always pretty smooth on gear change.