Whilst doing the 30K mile service on my 03 Forester, I did the "drain and fill" on my Auto tranny. Well, I did use ATF, not mountain dew or washer fluid, but I put Mobil 1 synthetic in with the regular atf that the car came with. I assumed it would be about a 60% 40% mix in there. I drove 150 miles or so, and suddenly realized what I had done. I checked with 2 tranny shops, and the dealer tranny specialist. All 3 said I needed a flush and fill. 96 bucks later, I have regular atf dexron III in there, and a clear mind.

So you put mobil 1 synthetic motor oil in? Or mobil one synthetic ATF in?

 

It shouldn't make any difference whether you have synthetic or regular ATF in.

I don't see a problem with your original plan. Mobil 1 ATF is compatible with the regular stuff. I did the same thing myself and the tranny is still humming hapilly along 15000 miles later.

Now, the stores you asked for advice, they did not have an incentive to mislead you, did they?

I put the Mobil 1 ATF in, so no problem there. All the shops I talked to had no incentive to get my business. The dealer farms out their tranny work to a shop that was closed at the time. All knew I was from out of town, and none offered to fix it for me, just giving advice.