Synthetic oils in ZF 6 speed.
11-27-2001, 12:16 AM
#21
Re: Synthetic oils in ZF 6 speed. (Corvette ED)
Corvette ED,
I doubt if "GM's cheapness" was a factor in their decision to continue selling conventional fill. The C4 was out of production long before BMW of America began using and importing the euro spec Castrol RS to the USA and long before ZF approved Castrol for the C4. Realize that GM was closely involved with the design, testing and development of the ZF and the original blend of the late '80's exceeded warranty and longevity requirements. This C4 OEM fill was plenty good for GM to recommend no fluid changes for 100K miles...and they surely will not revisit this decision in 2002. Castrol was still experimenting with synthetics when the joint Corvette ZF durability testing was conducted. ZF selected Castrol as a substitute just 3 years ago. Although some testing was surely conducted, ZF's close relationship with BMW induced the Castrol RS recommendation for the Corvette application. ZF has never recommended switching from GM fluid to Castrol RS. My continued use of GM fill stems from Boudreau's discouraging Castrol RS "viscosity stability" test results published here last year and the fact that RS synthetic motor oil (however impressive in an engine) was never GL (gear lube) certified. There really isn't any good comparison data published for the ZF app.
Any transmission with fluid over a year old with some miles on it will shift notably smoother with fresh fluid. Owners usually assume the brand of fluid made the difference. This rings like the comparison between 10 year old brand A tires and fresh brand B ones.
I doubt if "GM's cheapness" was a factor in their decision to continue selling conventional fill. The C4 was out of production long before BMW of America began using and importing the euro spec Castrol RS to the USA and long before ZF approved Castrol for the C4. Realize that GM was closely involved with the design, testing and development of the ZF and the original blend of the late '80's exceeded warranty and longevity requirements. This C4 OEM fill was plenty good for GM to recommend no fluid changes for 100K miles...and they surely will not revisit this decision in 2002. Castrol was still experimenting with synthetics when the joint Corvette ZF durability testing was conducted. ZF selected Castrol as a substitute just 3 years ago. Although some testing was surely conducted, ZF's close relationship with BMW induced the Castrol RS recommendation for the Corvette application. ZF has never recommended switching from GM fluid to Castrol RS. My continued use of GM fill stems from Boudreau's discouraging Castrol RS "viscosity stability" test results published here last year and the fact that RS synthetic motor oil (however impressive in an engine) was never GL (gear lube) certified. There really isn't any good comparison data published for the ZF app.
Any transmission with fluid over a year old with some miles on it will shift notably smoother with fresh fluid. Owners usually assume the brand of fluid made the difference. This rings like the comparison between 10 year old brand A tires and fresh brand B ones.
