Quote:
Originally Posted by hcch
It does not matter that we use ATF for a manual trans?
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Make sure to NOT use Dexron VI/Mercon LV or anything that's basically thinner, less viscous. You can find a lot more info on the Bobistheoilguy forums; but essentially, the additive package and friction modifiers in some popular multi-vehicle ATF such as Valvoline's Maxlife, is a bit TOO slippery for the synchronizers in the Tremec manual gearboxes. Something made for like the 8-10 speed automatics, is far too thin and has friction modifiers made for AUTOMATIC gearboxes, not manual (ex: Dexron/Mercon ULV, Lifeguard 8/9, Honda Type 3.1, etc.). You would be surprised at what I see people trying to put/use in their ATF-spec'd manual gearboxes/transmissions....
I, myself, tested it for a while, and it was okay at first and definitely was fine for cold start driving. But over time, it began to get notchy, and it would feel like it would want to crunch and grind as the trans began to get to operating temps (around the middle/180 F mark). You will really begin to notice the shortcomings when the fluid starts to overheat. If you are drag racing or track driving the car, you will most likely acknowledge the incompatibility of the ATF when you begin to beat on the car.
The (operating) viscosity of most Dexron LV/Mercon LV is also around ~5.8 - 6.1 cst, which is also lower than the ~6.9 - 7.3 cst that most Dexron III/Mercon V ATF's are rated at. At a minimum, you would want to run a "standard viscosity" ATF, which would also include ATF+4 as being okay. For those who don't already know, they just differentiate a bit between makes; with GM licensing Dexron, Ford licensing Mercon, and Dodge licensing ATF+.
Lots of people also find running Synchromesh MTF formulas to some of the best as well; it just hurts the cold start performance a bit, especially if you live in the colder climates. These are typically around a 75w-80 oil weight, and GL-4 rated. Do NOT try to use a GL-5 rated gear oil, which is what goes in the rear differential (hypoid gearing). At the least, you can use a GL-4+, which is GL4/5 compatible and safe for yellow metals; but I would just stick to a MTF-based GL-4 gear oil altogether, if possible.