Basically motor oil. Castrol TWS 10W-60 is what is recommended for ZF-6. That's used as engine oil in a few BMW cars.

GM 1052931 is the factory recommended lube, and its a 10W-30

Amsoil MTF , that meets the GM spec., is a 5W-30

I'm going to change the fluid in my ZF-6 today and use 15W-50 Mobil 1. $ 6.99 / qt. at wal-mart.

 

I'm pretty sure people have used Mobil 1 -- and their transmission didn't immediately "blow-up". OTOH, I don't remember anything about longevity reporting afterwards.

Don't make the mistake of assuming MTF is "basically motor oil". There are friction modifiers specifically targeted at making the syncro's perform correctly. Too much or not enough friction increases their wear rate/shifting force.

With that said, I can't say you're making a good/bad choice. However, it's not one I'd make. I'd pick a good MTF designed specifically for performance with synchros.

gp

BTW: A couple of yrs ago, I found a conversion chart that showed how 75-90w transmission lubes compared to engine oil weight. I was surprised at how close they really are. It's a different rating system.

 

I've been running the BMW Castrol for the last 6 or 8 years without a problem. Recently I did some research and decided to try Red Line Lightweight Shockproof Gear Oil. Redline is a 75W140 gear oil that has the lower internal fluid friction of a 30W motor oil. I haven't made the switch yet, but I'll post my results when completed.

 

Yeah, the BMW TWS 10w-60 replaced the RS. That oil is OEM spec for a bmw M3 engine. They probably run wide bearing clearances to need a 60 oil. Unlike gear oil there's no EP additive, like sulfurized olefins, viz., Lubrizol Anglamol(R) series.

To make a multi-visc oil like 10W-60 requires quite a load of polymer (VI modifier) which in the gearbox gets chewed up fairly quickly and is why the BMW 10W-60 quickly drops down to about a 40 level visc. after just a few thousand miles of driving in a ZF-6. My guess is that castrol uses group 3 base oils and can call the product synthetic due to a loophole in the labeling laws. MOBIL 1 is group 4 pure PAO base stock (fischer-tropf chemistry, liberated from the Germans in the late 40's). GM stock recommendation for ZF-6 has to be made to ensure low temp operation, like , down to - 40 degrees. My car, in Texas, will never get down that low so the 15W is no problemo. As for the 50 part, I bet the MOBIL 1 15W-50 will maintain its visc longer than the BMW TWS Castrol 10W-60. If that stuff is loaded with polymer, which it must be to give such a multi-visc rating, it gets chewed up real fast under the shearing conditions present - which MOBIL 1 15W-50 shouldn't experience due to its lower polymer content. I wouldn't do it if I weren't 100% sure within my own understanding, but would encourage others to learn to their contentment before embarking on such a choice. Its alot less expensive and may even be a superior choice within my environment. The 10W-60 can probably be relied upon to work in Alaska during a cold spell whereas MOBIL 1 15W-50 might be less desirable under those conditions.

I wouldn't exceed the 60 rating in hot visc. and I"m not sure I'd use a 75W, but only because I'm not familiar with how much the pieces in the ZF-6 expand and whether a 75W oil would cause a detriment on a cold trans.

 

TRANSMISSION OIL (status) - Vascular flow of oil through the porous Phosphorus-bronze (Pb) material of each synchronizer is essential for effective British Thermal Unit (BTU) heat exchange occurrence. Frequent transmission oil changes will ensure lower Pb particle levels suspended in the oil. The ZF S6-40 6-speed transmission is lubricated by engine type oil. Manufacturer recommendations specify the use of GM P/N 1052931 (5w-30) or BMW P/N 07510009420 (10w-60) oil.
Approximate oil capacity of the ZF S6-40 is 2.2 quarts.
FYI - the BMW 10w-60 oil is fully-synthetic and is used in the BMW M5 engine.

 

Yep. I think its recommended for four or five different BMW motors.

So the ZF-6 uses motor oil as a lube. Looks like a 5W-30 and a 10W-60 work just fine. 15w won't be quite as thin under winter conditions, but I don't encounter those since I left my snowshovel in Ohio in 97, before leaving LZ to do patent work. As far as keeping the lead particles in suspension, the dispersant technology is the same in all of them, polyamine bridged polyisobutyene-succinic anhydride adducts, "PIBSA". I'm not sure which group base oils castrol uses, but I am sure what MOBIL 1 uses and there is definitely less EVA co-polymer in it.

 

Just found this below, interesting article. Group IV oils are superior to de-waxed petroleum base stocks.

http://www.technilube.com/faqs_info/synth_diff.php

 

I take it all back, MOBIL 1 15W-50 is unsuitable. I was basing my conclusion on a piece of literature which stated the ZF-6 didn't require extreme pressure additives in its oil. That's wrong, as I just drained the trans and can smell it. It must be the BMW motors need that extra protection only found in the Castrol TWS and not conventional motor oils.

Using MOBIL 1 15W-50 as a replacement would only provide disappointment. At least I got to see what the trans fluid is looking like these days. Very clear and no particulates, but its only got about 8k on it. Good thing I cleaned the pan I drained it into before this fiasco, else I'd be grounded until Tuesday next.

 

I just took the advice of ZF-Doc and used the BMW Castrol 10w60 when I did mine earlier this spring. He knows a lot more than I do about the ZF-6...

 

That was one of the additives I couldn't remember. I believe you're correct about the pressure additives. I participated in a couple of threads in the 2005-7 timeframe. It seemed like we'd ruled out Mobil 1 as a optimal choice -- though there are people using it.

Redline, AMSOIL, and Royal Purple are among the manufacturers who make a suitable MTF replacement now that GM has discontinued their option. Pennsoil has also been mentioned -- though I'm not crazy about their lubes. As mentioned, the Castrol is recommended too -- though I didn't like the warm-up interval. For a few minutes each morning, I could feel a stiffer shift. I attributed this to the heavier weight.

Haven't used anything besides Castrol and the GM stuff.

gp