Mixing Oils

Urban legend has it that it’s bad to mix different motor oils in the crankcase. My question is about gear oil for the manual transmission, same weight but different brands. I’ve a half gallon each of two different brands and I’m too much a cheapskate to dump one of them. Our local police tells me I can’t just pour the extra in the river.

Yes, it is okay to mix them…and please dispose of the extra oil properly.

Mix til your hearts content…won’t hurt a thing.

Mixing two different brands of gear oil of the same viscosity is NOT a problem.
Go ahead and mix them.

The only mixing oil issues came from the early years of synthetic oils. It was only marginally true then and not at all true now. It is important that all the oil used meets the car manufacturers specifications (Usually like “SF”) Note: with only a few exceptions you can use higher ratings in an older car (SD is older than SF so you can use SF instead of SD.

Some urban legends are weaker than others but I think you found the least of them.

Mixing motor oils is OK. I have been doing if for years with no problems. We keep some of our cars for many miles before selling or trading; sometimes have three different brands and weights in an engine.

Not being a lubrication engineer, I can still guess that the reason you can mix gear oils is because they must be made compatible. When oil must be added, who could know with perfect confidence what brand of lube is in the transmission?

Go by what you owner’s manual says regarding using ATF or gear lube however. I would not mix ATF and SAE gear lube in a manual transmission.