924Board.org

[Dutch924-racer]

Recommend oil for a 931 snailshell is 75W90 GL5

But you can only buy semi synthetic and full synthetic.

which one should I take???

I have heard people say the gearboxes of classic/ older cars with copper/ brass parts in it are not compatible with full synthetic GL5 oil because it 'eats' the copper/ brass parts
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937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller

[Rasta Monsta]

Sure hope that's not true. . .I know there are a few people around here running full synth, myself included.
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Toofah King Bad

• WeiBe (1987 924S 2.5t) - 931 S3

[Smoothie]

I think I read here once that GL4 is ok, but GL5 isn't good for the copper..?
-Can't relocate the topic though.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Smoothie]

Here's that olde thread I was thinking about - http://www.924board.org/viewtopic.php?t=3096
My conclusion from that is that a gear oil with a "GL-5"-only rating can contain sulphur compounds that'll eat your copper. -But oils with the dual rating "GL-4, GL-5" should be ok. Both synthetic and dino are OK as long as they don't have "GL-5" as their only rating..
Sound plausible?
Makes sense to me as I've been using gear oil with the dual rating "GL-4, GL-5" for as long as I can remember with no ill affects.
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Dutch924-racer]

I looked at Valvoline oil bottles:

75W90 semi synthetic GL4

75W90 semi synthetic GL5

75W90 full synthetic GL3/GL4/GL5

So I think the last one is always safe, right ?
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937 trackday car
Series 2 engine
951S turbo and intercooler
Fast road camshaft
Forge recirculation valve + boost controller