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Gearbox/diff oil

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amrbose14

New member
I realise this is not an undiscussed issue but I'm trying to figure out what oil to get to change the gearbox/diff oil. The 'usual' recommendations of Swepco 201 and Redline are very expensive. And there I've even seen some suggestion that they might not be the recommended spec.

An alternative example appears to be Millers CRX SAE 75/90 NT. Considerably cheaper.

http://www.advantage-motorsport.co.uk/millers-oils-crx-75w90-nt-transmission-oil.html?gclid=CKb38fzvmsACFdLKtAode38ALA

But I'm really unconvinced that I understand what I am supposed to be looking for.

Does anybody understand the workshop manual specifications?

"SAE 75 W 90 to API Class GL5 or MIL-L 2105 B, or SAE 80 to API Class GL 4 or MIL-L 2105"

API GL4 and GL5 appear to be quite different: GL5 apparently contains an additive that forms a sacrificial layer on the gears. Does the viscocity rating of the oil change the additives required?

There appears to be some contradictory information around about the risks/dos-and-donts of mixing these different oil specifications. I'm guessing that anything new is better than the probably nine years since the last transaxle oil change!

cheers,
Chris
87 220T (non LSD - relevant here).



 
My understanding is that for slippery diff gearboxes you do need a fully synthetic oil due to the (potential) heat generated from the slipper plates. Having said that unless used hard on track days or for racing, very few 944's will really push the oil thermal ranges that hard.

I've always used 75w/90w Castrol Taf X, this has now been replaced by Castrol Tranx X 75w/90w.

Something to bear in mind is that the original Porsche Workshop Manuals were written 25 + years ago, oil technology has moved on significantly since then particularly the Nano Technology formulations from Millers. Porsche as a RWD car are fairly unique as most production cars (excluding exotica and the odd Renault) don't have transaxles with separate box & diff and different oils in each.

IMHO, new box oil every year or ~ 6K won't do any harm as all your doing is flushing out debris and scintered metal that acts as a grinding paste. Unlike engine oil gearbox oil doesn't get contaminated with combustion gases so should last longer, depends on how much TLC you want love on your 944 :)

Yours

Chris
 
SWEPCO 201 in my transmission. Its very viscous until warmed up, making the gear change very heavy and slow. Once warmed through, say 10 minutes of driving, its better than the Castrol semi synth I had previously.
 
Thanks. I might point put that the millers is about £20 against nigh on £70 for the swepco once vat and postage is factored in.
Chris
 
Personally I would go with the Millers oil :). It is good stuff, proven to work and proven in the field.
 
Hmm... the millers website recommends for 944 turbos:

http://www.millersoils.co.uk/automotive/tds-automotive.asp?prodsegmentID=38&sector=Car

Performance profile: "API: GL-4, GL-5"

The motorsport version is:

http://www.millersoils.co.uk/automotive/tds-automotive.asp?prodsegmentID=183&sector=Motorsport

Performance profile is much more comprehensive:

"API: GL-4, GL-5, MT-1
MIL: MIL-PRF-2015E
ZF: TE-ML-05B, TE-ML-07A, TE-ML-12B, TE-ML-16F, TE-ML 17B, TE-ML-19C, TE-ML-21B"


And much more besides:

"Designed for the lubrication of competition gearboxes. Manual transmissions, synchromesh, non-synchromesh, sequential gearboxes, transfer gearboxes and hypoid differentials without limited slip which require API GL4 or GL5 performance. Recommended for modern transmissions where fully synthetic oil is specified, especially for high performance road and track day applications. Hewland, Xtrac, Glebe Transmissions, ZF, Tran X, Elite Transmissions. Note: Does not contain friction modifiers. For plate type Limited Slip differentials use CRX LS 75w90 NT"

I'm all for reduced friction and power losses, but I wonder if that comes at a cost in terms of wear?

Chris




 
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