Transmission, Manual

Trans Oil Drain and Flush

Trans Oil Drain and Flush

I've a question regarding draining and replacing the 5 spd transaxle oil in my '88 S4. The car has not been driven for a couple months. I want to replace the Transaxle oil with synthetic. Now, after the car has set, all the oil has drained off the exposed gears into the case and can be drained. If I drive it for a few miles before draining, any contaminates may be stirred into the oil and may be drained out with the oil, but a lot of the old oil will still remain on the gears. Which is best. Drain without moving the car? Drive it for a few miles, then drain the oil?

Louis Ott
'88 S4 5 spd
'90 GT

Conventional wisdom says to run the car long enough to get the transaxle warm, then drain the oil.

Cold oil will flow VERY slowly, and won't carry the settled particles out of the transaxle, so the final removal of contamination would be higher with warm oil, even if it has been splattered around the case.

If you have serious contamination in the transaxle (not just normal wear particles), flushing will remove much more of the contamination, albeit with a very small additional risk of bearing damage. An effective
flushing solution can be made from three quarts of mineral spirits and one quart of Dextron. I would definitely get the transaxle warm if I were going to the trouble of flushing it. I would then drain the old oil, refill with the flushing mix, and run the car on jackstands (CAREFULLY!), going thru the gears several times. I would then let it drain for an hour or two, refill with the proper gear oil, and run it on the jackstands again.

Wally Plumley
928 Specialists

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