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Old 03-10-2008, 06:48 PM   #5 (permalink)
LostCause's Avatar
Join Date: Feb 2008
Location: California
Posts: 504

Thunderbird - '96 Ford Thunderbird
90 day: 27.75 mpg (US)
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Originally Posted by MetroMPG View Post
  • I also pour tested the factory original oil that I drained from the Blackfly (Firefly #2). It also poured through the filter at the same rate as the Synchromesh oil and 5w30 engine oil. Hmm!
This told me that the manual-recommended 75w90 synth oil I put in Firefly #1 was too heavy. Fortunately, I owned both cars simultaneously for a couple of weeks after getting the Blackfly (before selling #1). So I was able to do another test:[LIST]
75W90 is equivalent to 5w30 I believe. Transmission fluid and Engine oil use two different viscosity ratings. I don't know if it is common knowledge around here, but I remember being a bit mislead when I first read about transmission fluid.

I'm not refuting your results, nor can I explain why the change to synthetic brought such great results (other than less viscosity at lower temperatures).

I do know that transmission fluids are rated based on protection levels (1-5, but I've forgotten the exact name), therefore lower viscosity oils can essentially be equivalent to those much thicker. The lowest viscosity MTF I've seen is VW G52(which has a protection rating of 4), but ATF's are down there also.

G52 is not synthetic so it only has its rated viscosity @ ~100C. I believe VW also makes another extremely lightweight synthetic called G70 or something along those lines. Last I read about it, it was extremely expensive ($14/quart or something equally ridiculous).

I say run as low a viscosity as you are comfortable with and drive like you don't have synchros. Revmatch/double clutch...hard to master but cuts down on synchro wear/grinding.

Just imagine doing that @ 30mph...

- LostCause
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