I'm about to buy some transmission fluid from red line for my 89 GTUs. They suggested the D4 Atf, the lady said it's good for manual and auto which I think is sketch. I live in Washington btw. Which should I get?

 

Mt-90

 

Exactly. It's a GL4 oil just like the factory specifies. Only difference is the redline is 75W90 whereas I think Mazda specifies 80W90, but that's perfectly acceptable (just means the gear oil will work better when cold as it will start off slightly 'thinner').

Red Line Synthetic Oil - Gear Oil for Manual Transmissions - MT-90 75W90 GL-4 Gear Oil

 

So 80w90 tranny oil is better? I live in Cali where it gets hot. Specially this summer. I have a 89' GXL n/a (S5)

 

The first number is the "winter" viscosity rating. A lower number means that it will flow better when it is cold outside. For example, when it is cold outside, 75W will flow better than 90W. The second number is the regular viscosity rating. A higher number means that it will protect better when it gets hot. For example, in a high heat environment, 90 will protect better than 80.

Therefore, with everything else being equal, 75W90 will flow better than 80W90 when cold (75W is "thinner" than 80W), but both will act exactly the same when hot (both are 90).

If you have a street car then I would recommend MT-90. If you have a dedicated race car that is not street legal, then I would recommend one of the "shockproof" grades.

ATF is for modern cars with transmissions that are designed for ATF. For example, my 2000 F-150 uses ATF in its manual transmission. I would not put it in your RX-7's transmission.

 

Perfect. Thanks

 

atf in 5 speeds is a ford only thing from what i've seen in 95 and up cars. some hondas take 10w30 in automatics and manuals. the fluid is specific to the car not for all makes and models. the first number in gear oil is the weight, the second is how thick it will be when heated up by your trans or how long it takes to thin out called viscosity, not a winter summer number thing. please quit giving false info. your rx7 can take gl4 or gl5. we've been using the gl5 redline with the lsd additive already in it for our lsd diffs.

 

Yes

No, "weight" is a misnomer.

Somewhat

W does in fact stand for "winter", although the winter rating is for a cold-cranking / cold-pumping situation regardless of the actual season of the year. The absence of a W indicates non-winter as opposed to summer, but you could look at it as summer if you wish.

If my info is false, then I look forward to reading your white paper on revising the SAE J306 standard.

 

Evil aviator is correct.