The Honda MTF is like a 5w-30 and is thinner than GC 0w-30.
… … … … … … … … 100C … … 40C … cSt …
Honda MTF … … … … … 10.5 … … 53.2
Syntec 0w-30 … … … … 12.1 … … 66.8
Pennzoil Synchromesh … 9.08 … … 41.6
And it has a very high VI of 190 too, so it’s not likely that the Syntec would be thinner at winter temps like -30C. At -40C or colder the PAO based Syntec might be a little thinner ( Honda MTF = Grp II..?), but that’s probably not really relevant.
A motor oil has been spec’d in a fair amount of MT’s in the past but doesn’t seem to be much anymore. One could probably get reasonably good service life with a motor oil in a MT as long as the fluid was changed regularly, but motor oil is probably not really the ideal fluid for a MT because of the lack of EP additives.
My 1987 Jetta owners manual calls for a GL-4 80w-90 for the MT. These 80w-90’s are so thick in the winters here it almost amounts to a bad joke -- it’s like trying to shift a broom through molasses. They’d be ok in the southern US but are not really appropriate here. 75w-90’s help in the winters, but I find even they get quite thick around -25C which we regularly see in the dead of winter.
I just changed the MT oil in my Jetta 2 weeks ago, and in a effort to get something thinner I put in a 50/50 blend of 75w-90 and 5w-30 motor oil. The Petro-canada product handbook says a GL-4 fluid has about 50% of the additive treat rate of a GL-5 fluid. So, by blending a GL-5 gear oil 50-50 with motor oil, I figure I have a thinner GL-4 type fluid that has a good amount of EP additives in it. The 75w-90 is probably around 16.0cSt and the 5w-30 around 10.7cSt, so I’m getting a fluid around 13.0cSt -- thinner, but still quite thick compared to the Synchromesh fluids. I’m going to try this mix through the winter and see how it does. So far, my shifting is the best of any gear oil I’ve tried -- even better than the 75w-90 Synthetic I drained out.
The trend in MTF’s is definitely towards thinner and I’m surprised this hasn’t caught on more. These MT’s don’t really seem to need a 75w-90 GL-5 gear fluid. Despite the 75w-90 GL-4/5 spec’s for many VW MT’s, when I checked one of the VW forums there were a fair amount of users that were using Pennzoil Synchromesh with good results. Some of the new MT’s on VW’s are actually shipping from the factory with a 6.3cSt gear fluid. Someone over on the tdi forums did a UOA on his MTF and the results came back with 6.4cSt …!!! … -- he just about pooped his pants because he thought the MTF was a 75w-90 …
tdiclub …
.
Petro-canada makes a Duratran XL Transmission/hydraulic fluid that is 8.6cSt and is GL-4 rated. I’m probably either going to try this or the Pennzoil Synchromesh on my next transmission fluid change.