I saw that HPL offered ATF fluid in all PAO version for cold climates. Can somebody explain to me how that works? Normal ATF fluid is not PAO based? What does PAO do in cold?
PAO based ATF oil?
- Thread starter Rust_Belt_Pete
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PAO based fluid flows better than Grp III and Grp II at very low temps.
MIL SPEC 46167 is a PAO based 0W20 developed for engines and transmissions to cold startup at -60F. (Basically this was anticipating fighting the Soviet Union in Alaska or Siberia during the cold war.) We tested it a lot at Allison in military transmissions and it works as intended.
But unless you're talking temps like -30F and below, it's not a big concern.
There were a lot of Grp III based Dexrons that worked fine on -40 startups.
However PAO's also are more oxidation resistant which is beneficial if your system runs at high temps and/or you want long service intervals. The performance requirements of Allison TES-295/668 pretty much requires a PAO base if you're looking to find a Dexron type product.
MIL SPEC 46167 is a PAO based 0W20 developed for engines and transmissions to cold startup at -60F. (Basically this was anticipating fighting the Soviet Union in Alaska or Siberia during the cold war.) We tested it a lot at Allison in military transmissions and it works as intended.
But unless you're talking temps like -30F and below, it's not a big concern.
There were a lot of Grp III based Dexrons that worked fine on -40 startups.
However PAO's also are more oxidation resistant which is beneficial if your system runs at high temps and/or you want long service intervals. The performance requirements of Allison TES-295/668 pretty much requires a PAO base if you're looking to find a Dexron type product.
Question from the Slopster crypt:
Question 1: When choosing an all-PAO base oil ATF for a transmission fluid, how does one account for thermal expansion of the fluid?
Given that my ZF 8HP75 8-speed transmission in my RAM has the specific caveat of leveling the transmission itself and filling at the specified temperature range of 86 deg F - 122 deg F, does the thermal expansion difference between Group III+/mineral oil transmission fluid and PAO-based transmission fluid matter or cause any issue? (research says Group III+ transmission fluid expands 4% to 7% more than PAO-based transmission fluids).
While proper fluid fill level at temperature can be achieved with either fluid, will it matter if an all-PAO based transmission fluid is lower within the transmission housing at operating temperature?
Question 2: Given that the ZF 8HP75 (and 8HP70spec) transmissions rely heavily on precise friction behavior within the clutch pack, will Group III+ and Group IV transmission fluids require different levels of friction modification in order to allow proper clutch engagement?
Forgive me if I am overthinking this.
Question 1: When choosing an all-PAO base oil ATF for a transmission fluid, how does one account for thermal expansion of the fluid?
Given that my ZF 8HP75 8-speed transmission in my RAM has the specific caveat of leveling the transmission itself and filling at the specified temperature range of 86 deg F - 122 deg F, does the thermal expansion difference between Group III+/mineral oil transmission fluid and PAO-based transmission fluid matter or cause any issue? (research says Group III+ transmission fluid expands 4% to 7% more than PAO-based transmission fluids).
While proper fluid fill level at temperature can be achieved with either fluid, will it matter if an all-PAO based transmission fluid is lower within the transmission housing at operating temperature?
Question 2: Given that the ZF 8HP75 (and 8HP70spec) transmissions rely heavily on precise friction behavior within the clutch pack, will Group III+ and Group IV transmission fluids require different levels of friction modification in order to allow proper clutch engagement?
Forgive me if I am overthinking this.
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I'm not familiar with those ZFs but I assume they use a similar adaptive algorithm to everyone else. Which basically means the computer is looking at speed profiles and adjusting the solenoid pressures over time to adjust the shift to the optimized profile.
At Allison we had to be able to work with 15W40, 30W, and 0W20 engine oils, Dexron III, Dexron VI and PAO based Transynd.
At Allison we had to be able to work with 15W40, 30W, and 0W20 engine oils, Dexron III, Dexron VI and PAO based Transynd.
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