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I've done my due diligence reading through the threads on what fluid everyone is using in the ZF6. ZF Doc suggests Castrol TWS 10W60 which does not appear available anywhere. I've read good and bad on the Amsoil synchromesh. Same with the 88900333 GM fluid which is not fully synthetic. I'm a maintenance hog with my 96......so what's the consensus gentlemen? What's everyone using?
I just replaced the ZF6 oil in my 1989 with 75k miles. I put in amsoil synchromesh. Shift smoothness, especially into 3rd gear, got noticeably better.
I’ve read conflicting reviews of the Amsoil fluid. What did you have in it before? The previous owner of my car had the Castrol TWS 10w60 put in. Unfortunately that fluid is no longer available.
I do not know what was in it before, but if I were to guess I would hazard to say it was original GM factory oil. I bought the car as a quasi barn find at 58k miles. It was very very original at the time of purchase.
I would not hesitate to recommend Amsoil synchromesh. Simply put, it improved shifting over whatever was in there before.
I do not know what was in it before, but if I were to guess I would hazard to say it was original GM factory oil. I bought the car as a quasi barn find at 58k miles. It was very very original at the time of purchase.
I would not hesitate to recommend Amsoil synchromesh. Simply put, it improved shifting over whatever was in there before.
Nice. Appreciate the info. I’ve got 85k on my car, not sure how old the fluid is. I’ve got a receipt from years ago showing it was done but no mileage. I’ll most likely go with the Amsoil.
Nice. Appreciate the info. I’ve got 85k on my car, not sure how old the fluid is. I’ve got a receipt from years ago showing it was done but no mileage. I’ll most likely go with the Amsoil.
It could be argued and maybe correctly that if you're unsure of previous service, that regardless of your choice, you change, run for maybe a few hundred/thousand miles and then service again! Much might depend on the visual inspection of what you drain. I believe draining while at temperature is very beneficial.
It could be argued and maybe correctly that if you're unsure of previous service, that regardless of your choice, you change, run for maybe a few hundred/thousand miles and then service again! Much might depend on the visual inspection of what you drain. I believe draining while at temperature is very beneficial.
Solid advice . I think for peace of mind I’ll change it out with some Amsoil and check it after a bit. Them Germans build a fine transmission but they are picky with what you put in them.
The first time I replaced it, I used the Castrol TWS. The next time I used Amsoil. Both seemed fine with no issues. I couldn't tell if one was better than the other.
I thought it interesting that the ZF S6-40 is the 'only' ZF manual transmission that isn't included in the ZF Industries Specifications. I thought maybe they by now might have a ZF Lifeguard suggested fluid.
I also thought the MTL Viscosities deserved a look and these are from I believe 2008
Current MTL GL4 viscosities are:
1. ATF viscosity Series; 6.5 to 8.5 cSt (Equivalent ATF viscosity; Note: ATF additive package is weak compared to most GL4's)
2. Synchromesh viscosity Series; 9.3 - 9.6 cSt (such as Amsoils MTF, Texaco's MTL, Pennzoil's Synchromesh, GM and Chrysler's Synchromesh)
A differential lube may not kill your manual transmission in your light truck or car, but it is not the optimum lube for it. A differential 75W90 (GL5) lubricant usually has a higher viscosity than does an mtl in the same advertised weight.
The first time I replaced it, I used the Castrol TWS. The next time I used Amsoil. Both seemed fine with no issues. I couldn't tell if one was better than the other.
Another vote for Amsoil. Thank you for the info 👍🏻
I thought it interesting that the ZF S6-40 is the 'only' ZF manual transmission that isn't included in the ZF Industries Specifications. I thought maybe they by now might have a ZF Lifeguard suggested fluid.
I agree. I’ve read this trans was also used in the Viper. Not sure how correct my info is. Very odd they don’t officially list an updated fluid recommendation. I did see this on
the BOBISTHEOILGUY site. It’s what made me hesitant to go with Amsoil.
Another ZF6 Fluid Thread
