Rocketman

For My '88 N/A stock unmodified 2nd gen convertible, my mechanic recommended that I use:

Manual Transmission: Redline MTL (70W80 GL-4 Gear oil)

Differential: Redline 80W140 gear oil

Are these the correct redline products to use?

A second mechanic told me he doesn't use synthetics cause he's seen problems with these and I should use regular gear oil (70W90). Which is the truth? (I don't drive my car hard, and I just want it to last as long as possible).

Your help appreciated.

JohnSchindler

I've used the MTL for at least two years. I noticed an immediate improvement in the syncros during downshifts.

The trans needs some work now, but at 110,000 miles, some of it fairly hard, that seems reasonable.

jeremy

iTrader: (1)

i have a 91 gxl and the redline tech said mt90 in the tranny and 70w90 in the diff. that is also for autoxing too. i haven't had any complaits yet. i have no idea why he wants to put the 80w140 in your rearend.

SilverT2

Mobil MT90 in the trans and Mobil MT90 in the diff. Synthetic is quite better for colder climates FYI.

N1XRR

I had Redline for about 9 months till I changed my clutch and didn't have time/money to order some more Redline...I will once I start my new job...this stuff is GREAT for your synchro's.

Michael

Evil Aviator

I really like the Red Line gear oil. I used MTL (70w80) for a long time with good results, but the newer MT90 (75w90) weight is better suited to the RX-7 factory specs (80w90), so I'm using that now.

Maybe your mechanic knows something that I don't know, but I believe that the super-thick 80w140 is made more for stump-pulling than it is for street driving. I have used 75w90 differential oil on the street and autocross track for over a dozen years, and have had excellent results with this grade. BTW, the S4 factory manual calls for 80 to 90 weight oil in the differential, depending on the ambient temperature.

Synthetic oil, especially Red Line, is very good in the transmission and differential. However, Mobil 1 doesn't seem to work as well, and some people claim that it eats the synchros, although I have not been able to verify that claim.

Icemark

Mobil One has a very high sulfer content and will lead to your syncros disolving.

in addition Mobil One does not come in a MT90, only Redline does.

jeff88

Mobil One has a very high sulfer content and will lead to your syncros disolving.

in addition Mobil One does not come in a MT90, only Redline does.

If that is trye that SUCKS, because I just changed my tranny fluid to Mobil1 Synthetic.

I thought that most gear oil has sulfur in it. Anyone know more about this?

Icemark

Mobil One is a GL5 oil, not a GL4 as our tranny's require.

There is more to gear oil than just viscosity.

Evil Aviator

According to the FSM:
Transmission - API GL-4 or GL-5
Differential - API GL-5

jeff88

that is what I thought. So it will not harm the synchros?

RexRyder

iTrader: (10)

neone know about using redline motor oil? (synthetic)

RETed

Contact Redline themselves for recommendations - they will tell you MT90 for trans and 75W90 or 75W90NS (depending on LSD) for rear end.&nbsp I believe Redline should know which fluids are recommends for your vehicle.

http://fc3s-pro.com/TECH/REDLINE/redline.html

Sulfer additives are used to increase bearing load capacities in any fluid, dino or synth.&nbsp Yes, sulfates are added to synth fluids also.

Unlike engine motor oil ratings, the GL-4/GL-5 ratings do not supercede each other.&nbsp GL-4 is a specific rating for transmission fluids, and GL-5 is a rating for generic/universal gear fluid.&nbsp Most GL-5 fluids have sulfate additives; most GL-4 fluids do not.&nbsp GL-5 fluids are okay IF it explicitly states it's ok to use in synchromesh transmissions.&nbsp The whole hubbub about sulfates and trans fluids is that the FC uses bronze synchromesh components.&nbsp Sulfates attack/corrode bronze parts!&nbsp Dumping sulfate-ladden gear oil into a bronze synchro'd transmission will reward you with quickly degrading transmission performance (read:&nbsp grinding gears)...


-Ted

jeff88

Well that SUCKS! It is a PITA to change the fluid too!

I should have just used redline in the tranny, I used it in the diff. I had 4 quarts of Mobil so I used it.

Time for another tranny drain and fill.

Thanks for the good into RETed.

Rocketman

Thanks for the good info Ted!
I returned the MTL and 80/140 and changed them to
MT90 and 75W90 even though the guy swears by them!
I'll put them in in a few weeks and let you know how they work.

I've got 193,000 orrigional Kms (Yes, I've owned it since brand new!) and the tranny still works flawlessly. If any problems crop up right away, I'll know it is the oil.

downwinddave

My 89 was notchy to say the least. But not now.
My 91, I dont think anyone ever down shifted it. It would not go into 1st with out double clutching, now like butter.
Red Line made a HUGE differance.

inukai

Hi

I use RedLine.

As for top 3 tuner in Japan.

RE-A uses RedLine, even for GT car.
JUN uses NEO synthetic in CA.
KSP-ENG uses OBERON in Australia.

RexRyder

iTrader: (10)

what about motor oil (not tranny oil)

Evil Aviator

It's not worth paying $6-8 per quart x 5 quarts per 3,000 miles for the small advantage that the synthetic engine oil gives you unless you are a serious professional racer. Also, some brands of synthetic oil don't burn correctly in the rotary engine, causing striations to wear into the rotor housings, which is why Mazda recommended against using synthetic engine oil. Most people, myself included, have had excellent results with Castrol GTX in their rotary engines.

Synthetic oil is worth putting into the transmission and differential because you only change it every 30,000 miles or so, and therefore it doesn't impact your pocketbook as much.

inukai

Hi Evil Aviator

Every 30,000 miles !!
Is it normal in America?
We change motor oils and tranny, diff oils every 1000 km
to 3000 km.
Actually, some don't change oils over 10000 km (6000 miles).
I have overhauled some motors and trannies and diffs.
Regularly oil changed ones are in good conditions.

RexRyder

Yes.
All the three top tuners are using of their own choosing oils
for motors, trannies and diffs.

Personally I love NEO.
I would use NEO if I lived in the States.

Evil Aviator

Unless you have race cars, you are wasting your money and polluting the environment.

According to the Mazda Factory Service Manual

Engine Oil - Normal Driving Conditions
Non-Turbo: 7.5 months or 7,500 miles
Turbo: 5 months or 5,000 miles

Engine Oil - Unique Driving Conditions
Non-Turbo: 5 months or 5,000 miles
Turbo: 3 months or 3,000 miles

Gear Oil - Normal Driving Conditions
60 months or 60,000 miles

Gear Oil - Unique Driving Conditions
30 months or 30,000 miles