6MT Transmission Fluid Recommendations

[venturaII]

Originally Posted by n8dog11914

I went with Millers 75-90 (GL4/GL5) transmission fluid.

That is NOT compatible with our transmissions. I would strongly recommend you dump it immediately and refill with a proper GL4 rated fluid.

[n8dog11914]

Originally Posted by venturaII

That is NOT compatible with our transmissions. I would strongly recommend you dump it immediately and refill with a proper GL4 rated fluid.

It's no different than Motul that everyone else is running that is GL4/GL5 rated.

[venturaII]

Originally Posted by n8dog11914

It's no different than Motul that everyone else is running that is GL4/GL5 rated.

Okay. Knock yourself out.

[N234]

Originally Posted by venturaII

That is NOT compatible with our transmissions. I would strongly recommend you dump it immediately and refill with a proper GL4 rated fluid.

Care to elaborate?

[venturaII]

Originally Posted by N234

Care to elaborate?

Sure, it's really simple - if a fluid meets a GL5 rating (which is a rating for hypoid gears, not present in our transmissions), then it does so through the addition of ingredients which are incompatible with the soft 'yellow' metals that are present in our transmissions. So, while the typical axle containing hypoid gears can use GL5 (and indeed it is better performing in this application than GL4), transmissions do not fall under the same 'backwards-compatible' umbrella. This issue has been hashed out to the nth degree on websites dealing with older BMWs and other older vehicles whose transmissions were originally designed to use GL3 or 4. If you use GL5 fluid, it will 'work', but at the expense of shortened transmission life.

[TheVoiceOfReason]

Originally Posted by venturaII

Sure, it's really simple - if a fluid meets a GL5 rating (which is a rating for hypoid gears, not present in our transmissions), then it does so through the addition of ingredients which are incompatible with the soft 'yellow' metals that are present in our transmissions. So, while the typical axle containing hypoid gears can use GL5 (and indeed it is better performing in this application than GL4), transmissions do not fall under the same 'backwards-compatible' umbrella. This issue has been hashed out to the nth degree on websites dealing with older BMWs and other older vehicles whose transmissions were originally designed to use GL3 or 4. If you use GL5 fluid, it will 'work', but at the expense of shortened transmission life.

I agree for a fluid that is purely rated for GL5, but they are talking about fluids that are rated for both GL4 and GL5 that will not damage the syncros. Otherwise they couldn't rate it for 4 and 5 at the same time.

[venturaII]

Originally Posted by TheVoiceOfReason

I agree for a fluid that is purely rated for GL5, but they are talking about fluids that are rated for both GL4 and GL5 that will not damage the syncros. Otherwise they couldn't rate it for 4 and 5 at the same time.

I think you're missing the point that it's a hypoid gear rating, not a transmission rating. GL5 WILL work in an application where a hypoid GL4 oil was originally specified.

[TheVoiceOfReason]

Originally Posted by venturaII

I think you're missing the point that it's a hypoid gear rating, not a transmission rating. GL5 WILL work in an application where a hypoid GL4 oil was originally specified.

I understand the ratings. The point is, fluids like Motul 300 are rated to meet BOTH GL4 and GL5 specs because they do not attack yellow metals. Many people have been running on Motul 300 without issue for quite some time now.

Running something like Subaru Extra-S (GL-5) in the transmision would not be a good idea.

[venturaII]

Originally Posted by TheVoiceOfReason

I understand the ratings. The point is, fluids like Motul 300 are rated to meet BOTH GL4 and GL5 specs because they do not attack yellow metals. Many people have been running on Motul 300 without issue for quite some time now.

I don't believe you are correct in that assumption, but you're obviously free to experiment with your car. Personally, I don't want to be 50K into my ownership to find out that GL4/5 fluid is not compatible with soft metals, so the fluid I use is definitively labeled GL4 (only...) and is what Toyota says to use in that transmission. The only other fluid that I can think of that'd I'd even consider using is Amsoil's GL4 75W-90 transmission lube.

[504]

Anyone have experiences with redline mtl AND mt85? The mtl is much closer to the OEM viscosity specifications however 75w80 is under the recommended viscosity. The red color of mtl kinda scares me too gives me the impression that its very slippery like ATF.

Also I think a good point to bring up is how hot the tranny fluid gets i.e. if it only reaches 90c then the very thin pentosin mtf2 has possibly a 15cst thickness as opposed to the 7.7cst at 100c that everyone quotes.I think it would be a big contribution to this thread if someone could provide some form of quantifiable data on this

[Briankbot]

Originally Posted by 504

Anyone have experiences with redline mtl AND mt85? The mtl is much closer to the OEM viscosity specifications however 75w80 is under the recommended viscosity. The red color of mtl kinda scares me too gives me the impression that its very slippery like ATF.

Also I think a good point to bring up is how hot the tranny fluid gets i.e. if it only reaches 90c then the very thin pentosin mtf2 has possibly a 15cst thickness as opposed to the 7.7cst at 100c that everyone quotes.I think it would be a big contribution to this thread if someone could provide some form of quantifiable data on this

Maybe its not helpful to you, but see post #43 in this thread.

[504]

Originally Posted by Briankbot

Maybe its not helpful to you, but see post #43 in this thread.

will update this post with impressions

Edit:

Just replaced the fluid. I felt stock fluid was excellent, it would always let me in gear except maybe my first 2nd gear shift on cold days. The redline MTL feels very similar but a little less notchy and more fluid going into gears. downshifting from 5th to 4th used to catch sometimes and is a non issue now. The difference is subtle but noticeable which isn't a bad thing because I felt stock fluid was excellent. Fluid changed at 13000km; surprisingly both the diff (red) and transmission (yellow) still had color in them. Its great to remove break in metal especially after seeing all the non ferrous material in the differential. Highly recommended!


Further impressions: confirming my suspicions, it does seem the fluid is slightly slipperier than ideal. 2nd gear has a slight synchro catch sometimes (no grind though)

[2_slo]

Originally Posted by Jmonty

Pentosin FTW here in the Pacific Northwest.

Same here in the midwest. I switched to pentosin mtf2 25k ago and have not regretted it for a second.

[Xinshadow]

Originally Posted by venturaII

I don't believe you are correct in that assumption, but you're obviously free to experiment with your car. Personally, I don't want to be 50K into my ownership to find out that GL4/5 fluid is not compatible with soft metals, so the fluid I use is definitively labeled GL4 (only...) and is what Toyota says to use in that transmission. The only other fluid that I can think of that'd I'd even consider using is Amsoil's GL4 75W-90 transmission lube.

Just to chime in, after doing a TON of reading on the subject and some digging on the trannys of previous cars I've had, I'm inclined to agree actually. I ended up ordering Amsoil GL4 75W90 for the trans, and I'm using the Motul 300 for the diff.

Previous cars where I'd used Motul 300 don't have yellow metals in the trans upon further research so the GL4/5 worked great. For the 86, it was worth it to stick with a GL4, if only for the peace of mind as I want the car to either A die a viking death on the track or B last a good long time, don't want to have a nagging concern about destroying a tranny down the road.