The question has been asked various times. What is a good aftermarket replacement for the stock GM fluid in the MU3 Transmission? And conjecture is its 75w90, or syncromesh, or ATF , etc. The GM part number escapes me but according to GM Powertrain the MU3 uses Castrol Burmah BOT 0063...I have a email into Castrol to get the specs on this fluid and will post those when I get them. However I have researched this and come up with the GL-4 standard in other places...this means the fluid could be 75w90, or 80w90. If anyone has any specs on the BOT 0063 they would be appreciated.

 

You'll get some people swearing by the Royal Purple stuff but seeing as a few of them have gone through a couple of trannys that should ring some bells.

I would use exactly the same fluid it came with. It doesn't matter if it shifts "way smoother". If a fluid switch is changing the feel of the tranmission that much vs. stock then clearly that fluid is alot different and most likely out of spec.

Stick with the reccomended stuff as its been tested thouroughly for years and you'll enjoy a lasting transmission.

 

well according to castrol who makes the GM fluid for the MU3 there is NOT an equivalent to it

so 75w90 is NOT equivalent

because they make a synthetic 75w90
http://www.castrol.com/castrol/secti...tentId=7036193

 

... your absolutely right...

From Castrol's website

 

yep there is no equivalent to the BOT 0063

 

Nice job, thats some convincing proof.