Mixing Transmission Fluids?
 

I looked around this forums and other forums and got the impression it is OK to mix fluids as long as they are both synthetic. My question though is is it OK to mix a 75w-90 with a 75w-80?

I bought 2L of Pentosin MTF-2 (75w-80) and 2L of Motul 300 (75w-90) and since the transmission requires 2.2L and the rear differential requires 1.2L I didn't want to buy an extra Pentosin if I didn't have to.. (pretty damn expensive).

People have used a lot crazier cocktails before (see uncle scotty's cocktail) for various reasons. It probably won't hurt anything, but I'm not a real FR-S owner: I only play one on TV.

On a side note, if you had bought three of the Pentosin, you would only have to buy two more next time (assuming you use it again *I know I will*) since you'll have enough left over from previously. You're going to be in the exact same spot then as you are now.

I'll probably just mix it, .2L of a slightly different fluid seems OK. As for buying another one it would be a an extra 30 some dollars for something I won't use for another 2 years or ~30k miles and I'll probably end up losing it somehow lol.

It's the same as mixing 89 and 91 octane gas... as long as additives in the oil do not combine to create a more hazardous compound (and there'd be a warning if this was a remote possibility), you're fine.

-alex

BITOG gives it's blessing:
http://www.bobistheoilguy.com/forums...Number=2630524

Mixing engine oil is different and most API certified engine oils are mixable. Most Subaru owner's manuals recommend against mixing gear/transmission oils.

Mixing Pentosin and Motul are probably fine, but I would do more research. Check the ATF, Diff, Trans forum at bitog and make a new post if you can't find anything. If you're lucky, you may get a reply from someone that works with gear oils for a living.

-Dennis

And Uncle Scotty's cocktail? Subaru owners have been using that for years.

I do understand what you're saying though, and I realize this is not the same transmission for which that home-brew originated.

Some owner's have had problems with it as well. Look up the virgin oil analysis of that on bitog.

-Dennis

When you drain the trans you can't get everything out, so you're already mixing a small amount of the new oil with the OEM oil anyway. Unless your flushing with some type of solvent which I wouldn't recommend.