Somehow my transmission developed a rather large thirst for MT90 tonight when I finally decided to do my yearly flush. The normal 2 bottles wasn't enough! I panicked and took the rest of the 75w90 I had (for the rear diff.) and tossed it in. This shouldn't have any adverse affects, should it?

I am aware of the elephant in the room that is the GL5 vs. GL4 thread ( https://www.rx8club.com/series-i-tech-garage-22/gl5-vs-gl4-gear-oil-transmission-159398/ ), but saw no mention of the intermixing of the two.

 

It will work.

 

I've done it before. Two bottles of Redline (GL4) went in the transmission and it didn't start to overflow. I had some leftover of Royal Purple (GL5) from doing the limited slip differential oil change. So I put the rest of the RP into the transmission.

For people who want to use RP (GL5) in their transmission but are paranoid that it might eat up the synchros or whatever, a cocktail of GL4 and GL5 might be interesting.

Many people have reported the shifter being sticky when it's cold when using Redline. But a few people have reported slicker shifting when it's cold, and I'm one of them. I've wondered if it's because around 15% in my transmission is Royal Purple GL5.

 

Thanks for the assurance, guys.