So today I replaced my transmission and differential fluids with Redline MT-90 and 75W-90 respectively I have access to a shop with lifts and a full set of tools so I used their fluid pump. But of course the last person to use it didn't let it drain so I purged it with just a bit of the MT-90. And of course I was about 0.1-0.2 quarts low when I ran out of fluid. Instead of leaving it low, I opted to top it off with the 75W-90 since the weights are the same and only the additives differ (I assume). Is it probably okay, or am I looking at imminent component failure?

 

You'll probably be fine I would guess. I just did the fluid replacement myself today. The guy that used the pump before me didn't drain it either, so who knows what the heck my redline is mixed with really (probably 80w-90 actually), but I don't think it would have been enough to make a difference.

 

Thanks, I hope you're right. I managed to get about 10 good pumps of the 75W-90 diff oil in. Maybe I'll swap it out next time I'm in for an oil change... and this time I'll use my own pump.

 

it won't make any difference

 

The manual says you can use 75W-90 GL-5 in both Trans and Diff.