ZF fluid change Redline MTL vs castrol vs GM.... I am confused

[Paul G]

I have done a little research through the archives on which fluid to use. I now know more about it than I wanted to know, and am more confused than when I started!
I guess there are three choices:

The GM recommended fluid.

The Castrol 10W60. Is this actually engine oil?

Redline MTL.

I can get any of these. Chevy dealer is the closest. BMW dealer 5 minutes further up the road. Redline I can get from Summit which would be delivered to my door. Prices are within $5 of each other for 3 quarts so price is not really a consideration.

Which fluid will give me the longest life and smoothest operation from my ZF?

 

[94C4]

I've been told that the GM fluid is Mobil 1 5W30. The same stuff that is in the engine.

 

[Tuna]

When I switched to RedLine MTL, my ZF got a lot smoother and quieter. That's my choice.

 

[ßill]

Ditto what Tuna said. Put red line MTL in mine ant I'm happy!

 

[Paul G]

I ordered the Redline MTL from Summit today. Thanks guys.

 

[wx briefer]

I have refilled twice. First time with GM stuff and I noticed no difference. This last time I used the Castrol tws 10-60. I noticed a big difference with smoother shifting.

 

[ProEMTPFF]

Don't forget Royal Purple! I use it for all my fluid needs and love it. I used to be a Redline guy.

 

[Hib Halverson]

The GM lubricant for the ZF S6-40 is a 5W30 engine oil. As the original lubricant was developed jointly by GM and Texaco, it used to be sourced from Texaco and was a petroleum-based, Havoline 5w30, but when Texaco discontinued refining that product about 1999, GM SPO went to another supplier and I, while I know it's still a 5W30, I am unaware of which refiner is the supplier.

The Castrol 10W60 is, indeed, an engine oil. It is supposedly used in the in-line six in the BMW M3, among other applications. While the Castrol was not tested or approved by GM for use in the ZF, ZF Industries endorses it for use in the S6-40. My information is that, while a good choice for shift quality and transmission reliability, the oil is not that durable. I believe Bill Boudreau, the "ZF Doc," ran it. He had some spectographically analyzed after 10,000 miles and, based on the test results, felt the lube needed to be changed.

I recommend Red Line MTL for use in the ZF in most duty that transmission will see. I tested it for several years back in the late 90s and felt it worked very well. Shift effort went down slightly and shift quality was very smooth. My change interval, based on spectographic oil analysis was 3yrs or 36,000 miles.

Currently, I use Red Line Light Shockproof in ZFs, however, that lubricant is a very severe duty lube intended mainly for race track use. While it offers the ultimate in lubrication and protection, improved shift effort and a slight reduction in gear rattle it 1) doesn't meet any warranty requirements (not that any ZF is still under warranty, at this point) and 2) ZFs using LSP have slightly higher shift effort than they do with MTL when the trans and lube are cold.

 

[slapshot]

this is actually one of the next things I need to do, this and change the rear end lube. How hard is it to do??

 

[NinetyFiveVette]

Hib-

Thanks for the information. I am currently replacing my A4 with a ZF6 and have been contemplating which lube to fill with before I install the transmission next week.

I doubt I will see much severe duty use, but I am going with McLeod's street twin with aluminum conventional flywheel. The gear rattle reduction qualities with the Redline LSP interests me since I know I will be getting my share of gear rattle not using a dual mass flywheel (though it might not be audible over my exhaust). Would you recommend the LSP in my application or still the MTL?

Thanks,
Mike

 

[Vettelt193]

The GM lubricant for the ZF S6-40 is a 5W30 engine oil. As the original lubricant was developed jointly by GM and Texaco, it used to be sourced from Texaco and was a petroleum-based, Havoline 5w30, but when Texaco discontinued refining that product about 1999, GM SPO went to another supplier and I, while I know it's still a 5W30, I am unaware of which refiner is the supplier.

The Castrol 10W60 is, indeed, an engine oil. It is supposedly used in the in-line six in the BMW M3, among other applications. While the Castrol was not tested or approved by GM for use in the ZF, ZF Industries endorses it for use in the S6-40. My information is that, while a good choice for shift quality and transmission reliability, the oil is not that durable. I believe Bill Boudreau, the "ZF Doc," ran it. He had some spectographically analyzed after 10,000 miles and, based on the test results, felt the lube needed to be changed.

I recommend Red Line MTL for use in the ZF in most duty that transmission will see. I tested it for several years back in the late 90s and felt it worked very well. Shift effort went down slightly and shift quality was very smooth. My change interval, based on spectographic oil analysis was 3yrs or 36,000 miles.

Currently, I use Red Line Light Shockproof in ZFs, however, that lubricant is a very severe duty lube intended mainly for race track use. While it offers the ultimate in lubrication and protection, improved shift effort and a slight reduction in gear rattle it 1) doesn't meet any warranty requirements (not that any ZF is still under warranty, at this point) and 2) ZFs using LSP have slightly higher shift effort than they do with MTL when the trans and lube are cold.

I thought ZFDoc came to the conclusion that any oil would need to be changed frequently because of the synchros.... I remember him saying something like, until someone invents a copper magnet, tranny oil should be changed at 10k miles.

 

[Strick]

It's an easy change. Why not take a few minutes and change it when you change your oil? I do mine everyother oil change and I use the GM stuff.