'91 Audi Coupe 7A Manual Transmission and Rear Gear Oil

[cgharibo]

The manual transmission hooked up to 7A has 310,000 miles. The fluid has only been changed once at about 120,000 miles. There are no leaks.

Do I need to change the MTF and gear oil? Actually, never mind! I want to change the MTF and rear axle oil.

I used Audi oil long ago that is no longer available. I remember using Redline and shifting was noticeably poor in cold weather. I changed back to Audi oil (G50?) and shifting improved greatly.

What should I use this time around. I live in a 4 season environment and can drop as low as -10 Fahrenheit.

I see below listed:

Moly 75W90 Fully Synthetic Hypoid Gear Oil
Motul Gear 300 LS 75W90 (1 Liter) - Motul 105778
Audi VW Gear Oil Synthetic 75W90 - Genuine VW Audi G052145S2
Mobil 1 104361 75W-90 Synthetic Gear Lube

Thank you!

[Tractor Dave]

Can you get Castrol syntrax 75/90? Very good stuff. Just don't use a GL5 in your gearbox due to sulphur and brass synchro. Rear diff EP90 gl5 of high quality.

[cgharibo]

How about MOTUL 300 75W-90 for MTF & rear differential?

[cgharibo]

There is highly conflicting advice on what kind of MTF and rear axle oil to use on 1991 7A cars. The dealer recommends G052145S2 which seems to be nonsynthetic and inferior to G50. Motul 300 seems to have cold shifting issues.

Last time I strayed outside G50 at about 100,000 miles by changing to Redline resulted in very poor cold shifting. Changing back to G50 fixed the poor cold shifting.

My MTF has G50 now. The car has 310,000 miles.

Cold weather performance is key for me.
What's my best MTF and rear axle option here for a cold environment that drops to -10 fahrenheit?

Thank you!

[Tractor Dave]

We don't get those sort of temps over here very often but the castrol oil I mentioned above is well known for its smooth cold shifts. Maybe send them an email and see what they say about its cold performance. Recently changed its name to transmax.
https://www.castrol.com/en_gb/united...ne-fluids.html

[K Simmonds]

I've always used genuine VAG mineral GL4 in the gearbox and their GL5 for the rear dif and been very pleased with the results, that said we don't get temps that low over here so you maybe better off with something thinner in the gearbox. The coldest temp I've ever run either my RS2, now dead 3B S2 or B3 80 at is -10C which is about 15F so nowhere near as -10F, that's bloody cold!

However I'm in the trade and get my all my oils from TPS when they're on special offer, I use their semi sythectic 10W/40 in all my cars engines apart from the RS2 and G60 which both get fully synthetic Fuchs Titan race oil.

The Castrol oil Dave recomends is good stuff, though it is a fully synthetic GL5/4. I like Castrol products and have never had any issues using them at work.

Perhaps ask for advice from either a local workshop who you trust or try the oil companys.

I have enough genuine Audi oil in stock for a at least a few changes, personally I'd go with what they suggest do be too bothered by marketing data.

Make sure you can undo the fill plugs before you drop any oil out.