Fluid for a WC T5

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Feb 6, 2012
Raleigh, NC
Ah yes, the venerable T5. The problem is that, since this tranny is so common, everyone and their brother has their own opinion of what fluid works best in them. Tremec recommends non-synthetic DexIII ATF. Some people claim an MTF like synchromesh or honda MTF is best. Some people claim 10w-30 or 10w-40 motor oil is the best. I trust this board more than any other, so what is the general consensus for T5s? This particular T5 is in a 2007 mustang. 75k miles, factory fill was replaced with pennzoil multi-vehicle ATF at about 45k. The reason I'm interested in going heavier than ATF is because it seems a bit noisy. Not gear whine--it's quiet while in motion. But in neutral or at low rpm it seems to sound a bit "rattley," kind of like marbles rolling in a coffee can. Also, I just want to maximize the life of the tranny and I've heard other fluids protect better than ATF. What is the BITOG feeling about T5s?
Every manual tranny I`ve ever owned has had that rattly sound while in neutral. It`s just the tranny`s internals spinning. Keep the spec`d atf in it.Thicker than spec fluid will either make your gears crunch,or make it hard to shift between gears.
Ah, good to know I'm not the only one with that sound. We also have a VW jetta with a manual tranny and it's totally silent in neutral, but it's FWD so the tranny is much further away from the driver. I assume that accounts for the noise difference. Does it make sense that tremec doesn't recommend synthetic atf? I would guess that a manual tranny isn't that hard on the atf anyway.
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I think the VW is quiet,because it`s a fwd and the tranny is up front,whereas the Mustang`s (and my Z`s) trannies are right up under the console since they`re rwd,thus being able to hear the noise more since you`re right on top of the tranny.
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