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Transmission oils

I periodically drain my autotransmission of however much will drain, of course the torque converter does not drain, and refill. Somehow I wound up with about a quart of Chevron trans oil and about 2 1/2 qts of Pennzoil. Is there any good reason not to mix these in refilling?

As long as they’re the same type of tranny fluid, ie Dexron/Mercon, ATF+4 etc, there’s no reason they can’t be mixed.


If half of the old fluid remains in the transmission, the next drain and fill (after the vehicle has been driven) will result in 3/4 new fluid and 1/4 old fluid. Then, after that, 7/8 and 1/8, … ad infinitum.

As long as you don’t have to buy Pennron fluid for your next change, you should be OK. Or was that Chevzoil? Dude used to have a Yamaha with a Suzuki shifter on it. He called it a Yamazuki. He was from Hog Town Creek. (Gainesville Fl.) They called him Crockergator.

What Type Of Vehicle, Make, Model, Year, Is This?

What specific type of fluid is called for by the manufacturer? You can really screw up your transmission with the wrong fluid. Period. If these two fluids are both of the correct type, I don’t see a problem. It sounds like that is the case because you have used them before.

Put Dexron or Mercon in where it calls for ATF+3 or ATF+4 and you will have problems, for example.