I know a lot has been written about the importance of changing tranny fluid and how to do it properly, but I'm wondering why and why so often? Just about all modern cars(especially Asian cars) say it's not necessary, under normal driving, unless the oil gets contaminated. Volvo says every 25,000 miles, but that's for a 23 year old car. Could it be the oils from 23 years ago just broke down after so many miles and couldn't lubricate anymore? With the new synthetics I don't see that ever happening. My oil looks absolutely brand new but according to my speedo it's almost time to flush. Any thoughts?

 

Auto trannies work hard and get very hot. 25k is may be a little overkill, 40k is probably just fine for our cars' AWs--they are great units.

The recent wave of Euro cars saying "never change the fluid, it's for life" caused failures with 100k, and is now widely acknowledged to be a scam designed to make you buy a new car. Same for coolants, etc. The only fluids I don't sweat changing are in manual trannies. Those normally don't seem to deteriorate much under normal use...

 

Ok, I get what you're saying, but it still poses the question of why even change at 40k? The oil looks brand new. It's not contaminated. What happened to it that it needs to be changed?

 

Valid question but unfortunately only a lab can answer that with definitive authority.
I go through a lot of cars and I look at the color, smell, and feel of oils and if they pass those tests I leave them alone. Cars I have had for a long time I tend to follow the prescribed maintenance schedules.

 

Ok, what do you think about synthetic tranny oils? Any benefit?(I'm thinking heat)

 

I don't do synthetic in trannies so far. I use full syn in motors most of the time, trannies I go by the recommended types. With the AW, what's the point? A change every 40k should give you 300-400k miles with non syn... Also, cost wise, one uses 10-12qts in a change. But, I don't know what it'd hurt to try synthetic...

Some cars, like Mercedes, take only special fluid for the trannies you can only get at the dealer, so I don't try to second guess. Volvos are pretty forgiving.

 

I guess it's similar to engine oils - less changes with synthetics - but more cost. Buyer's choice.

 

I am in the habit of doing a drain and fill every 20-20k miles...with most of my cars they shift pretty much the same after a fluid change, but I had a Ford ZX2 with a Mazda automatic in it, and the difference with fresh fluid was amazing...it shifted like butter for awhile, but within 15,000 miles or so it was feeling rough again. I wound up doing frequent fluid changes as a sensory/satisfaction issue on my part, and for my benefit more than the car's benefit.