Just did a virgin oil analysis on a new bottle of BMW MTF LT-4 and got the results below: Also below is used oil analysis at 36,000 miles of what is supposed to be LT-4 also - this is in my 2009 JCW Clubmanwith 36K on the odometer: I was surprised by how thick the unused OEM fluid is (100C 14.8 cSt, 40C 70 cSt, with calculated VI of 223 ! ) Also surprised by how much it thinned out over 36K (100C 7.7, 40C 40.3) - still good numbers for a 6-speed Getrag. I was wondering if the previous owner added to or changed the gear oil from the factory fill, but he says no. Zeng on BITOG says (s)he's not surprised by the drop given the amount of viscosity index improver it must have to acheive 223 VI and that it just sheared down with use. Wondering if I should change it now with new LT-4 (have some), or use a more durable synthetic oil like Redline MT85 (75W85) (viscosities 12 and 62, VI 198) or Amsoil Manual Synchromesh Transmission Fluid MTF (5W30) (viscosities 10 and 50, VI 196), or something else entirely, or wait a year or so more to change it?
I can't find any proof that Amsoil is any good, all there is on google is a lot of hype. Also, I'm not buying oil out of someone's trunk.
My son ran Royal Purple in his mustang. We had seen videos of test with different oils. Royal Purple did very well.
I referenced BITOG in the opening post with comments by Zeng there. Here's a link to the ongoing thread that I started there - currently 19 posts so far: https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/5111099/specs-on-bmw-mtf-lt-4#Post5111099 Actually, I was hoping for a more robust multi-person discussion there.
Honestly.......use whatever you feel comfortable using. Then change it regularly depending on use. I don't believe there is that much difference in the products, as long as it is maintained.
After thinking about all this for a while, I'm going to just stay with the BMW MTF-LT-4 and change it every 25-40K. It has a very high VI which overrides my concern about the high-ish 100C KV (non-tracked manual transmission fluid doesn't usually get nearly as hot as motor oil anyway) and even though it shears down a bit with time and miles, more frequent changes will take care of that just fine. Also, I already have a few bottles of it.
I changed the transmission fluid (thought to be old LT-4) to new BMW MTF-LT-4 recently. I was puzzled by the apparent big drop in viscosity in the old oil until I did some googling and noticed that the additive amounts (Calcium Phosphorus, Zinc, Magnesium) were very similar to Texaco MTF-94,which of course is commonly used as factory fill for lots of MINIs. I'll bet the factory doesn't pay much attention to whether the transmission has an MTF94 or an LT-4 sticker on it (like mine does) when they fill it. It's also much more believable that the viscosity would drop from 10.4 (MTF94) to 7.7 in 37K than from 14.8 (LT-4) to 7.7. Actually, if I knew it had MTF94 in it I would have let it go to 50K and change it with MTF94 then. I guess it's much of a muchness anyway. I'm happy staying with the more robust LT-4 that's in there now and recommended for my MINI anyway.