Hi folks,

I've got an 1987 NA with 5 speed and am thinking about changing the gear oil in the trans. I live in the midwest just outside of Chicago so we see a range of temperatures, well below freezing up to 90's in summer, as I'm thinking the weight of the oil might be temperature dependent. Any suggestions out there as to what weight of gear oil and what type in general would work the best?

 

Yes, transmission oil, differential oil, engine oil, and the coolant mix are all temperature-dependent. You can find the Mazda-recommended fluids in the free online Factory Service Manual (S4) at one of the links in the 2nd Gen FAQ:
https://www.rx7club.com/showthread.p...18#post5131218

For your region I recommend a multi-grade oil. This is indicated with two numbers, one of which has a W that stands for Winter. For example, 80W-90 means the oil is rated for 80 viscosity in winter temperatures, and 90 viscosity in summer temperatures.

I also recommend using synthetic oil in the transmission if you can afford it. Synthetic oil helps fix the notchy 2nd Gen RX-7 transmission, and it works especially well in cold weather. The extra cost isn't that bad if you consider that the oil will last for 30,000 to 60,000 miles. Popular brands include Red Line, Amsoil, and Royal Purple. I don't recommend Mobil 1 because it has been known to eat synchronizers. Since synthetic oil is especially good at low temperature, a lower winter viscosity is fine. For example, 75W-90 synthetic will work well when 80W-90 is specified.

Here is what I use in my 88 RX-7 in St. Louis:
Engine oil: Castrol GTX 10W-40
Transmission: Red Line MT-90 (75W-90)
Differential: Red Line 75W-90 Gear Oil

 

Redline mt-90 for sure

 

By transmission, are you referring to the GearBox?

 

Yes, in American English we usually call it a "transmission" if the gears can be shifted, and we usually call it a "gearbox" if it is limited to only one ratio. However, sometimes the British term is used in the USA, so if you use the word "gearbox" then Americans will still understand.

What British English calls a "transmission", American English calls a "drivetrain". In this case, the British term is never used in the USA, so if you use the word "transmission" then Americans will think that you mean just the "gearbox".

 

Oh. Now I understand. Thank you for the English lesson

I would like to take this chance to ask you on advice for the lubricant for the rear differential on my 1987 Mazda RX-7 FC S4 Sport:
As you probably know, this car has a Standard diff, and the FSM says:
Above -18ºC (0ºF): API GL-5 SAE90
Below -18ºC (0ºF): API GL-5 SAE80W

However, here in Portugal I'm having a hard time on finding any SAE90 oil. The only oil's I've found so far, are:
80W90
75W90
SAE80

and they are all API GL-5

What should I do?

 

Use 80W-90 or 75W-90. The manual specifies 80W-90 for all seasons because it acts like SAE 80 in the cold or SAE 90 in the heat as I explained earlier. The 75W-90 will also work, and will flow better in the cold. The 75W-90 is probably synthetic oil, so it should work better overall.

 

Yes, I've found out that same page:


But I think that you'll find out that, that section is about the GearBox? I was talking about the rear Differential.

 

The differential is the same situation so you can use 80W-90 or 75W-90.

For limited-slip differential (LSD):
- Use gear oil with friction modifiers:
http://www.redlineoil.com/product.aspx?pid=133&pcid=4
- Or use regular gear oil and add friction modifiers:
http://www.redlineoil.com/product.aspx?pid=47&pcid=7 and http://www.redlineoil.com/product.aspx?pid=41&pcid=4

For open differential:
- Use gear oil without friction modifiers:
http://www.redlineoil.com/product.aspx?pid=47&pcid=7

 

Allright. Thank you Evil Aviator for all the information and help!

Cheers!

 

good info

 

Thank for all the good advice guys, the notchiness that Evil Aviator mentions is just what what I seek to remedy, as its quite apparent the first couple miles of driving these days, hopefully some synthetic gear oil does the trick.

 

I'm so glad someone asked this and not me lol.