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Synthetic auto transmission

Planning to start using synthetic auto trans fluid, by pulling the drain plug, then refill with synthetic. I know that not all of the fluid will drain, and the resulting fluid will be “mixed”. Anybody have any ideas on this, and/or what is the best synthetic to use? Thanks, Marty

If you’re a gambler, go ahead and do it. Tranmission fluids are formulated for each vehicle application. And adding a fluid that doesn’t meet the specs for that transmission is asking for trouble. Look in the owners manual for the proper type of transmission fluid that should be used. And stick with that.


Without knowing what car make model year and if more than one possible transmission there is no way we can offer any advice other than don't even think about using something that does not meet the specifications provided by the manufacturer of the car.  Modern transmission are a little too complex to wing it when choosing lubrication materials.

Use anything other than exactly what’s specified for your vehicle and you do so at you own peril.

Use the proper fluid, do the work properly, and your chances are excellent that your tranny will outlive your car. Well, perhaps not if you drive a Chrysler, but that’s a story for another post.

The opint is, use the correct fluid. Don’t second-guess the designers.

I think doing this is a cheap tranny insurance. Many cars/trucks now have synthetic in them from the factory if what one mechanic told me is true. In my 2001 Silverado, I had the trans filter and fluid changed at 50,000 miles and every 50,000 after that (now at just over 170,000) with Mobil 1 synthetic fluid that complies with the truck’s requirements. So far the transmission seems to be running fine. This is one of the rare things I have done at the dealership and they tell me that my transmission is still “tight” (whatever that means) with no slop that can come on with age. When I went to have the same thing done to my wife’s Ford 500 (2007) was when I was told that it alreqady had synthetic in it, and that 25,000 miles was too soon to have it changed.