996 manual gearbox oil options

[Paynewright]

Probably been done to death but what is the latest thinking on oil for a road car.

Google brings up Mobil and Shell as OEM fill oils. Best I can find which is readily available is Mobilube SHC 75w90 fully synthetic.

Can of worms truly opened!!

What are the PH recommendations?

Ian

[CarreraLightweightRacing]

Porsche recommends Mobilube PTX or Shell Transaxle, both 75W-90. I'd stick with these.
Reasoning:
Gearbox oil these days is quite gearbox-specific, much more than engine oil.
Porsche gearboxes are quite unusual in that they contain both the gearbox and the differential. Normally, differentials want hypoid API GL-5 oil, which is very low friction and withstands the extreme pressures of the differential. This low-friction GL-5 is not ideal in a normal gearbox, because the low friction doesn't let the synchromesh work properly. Therefore, normally gearboxes take GL-4 oil and GL-5 oil is not recommended. Unfortunately, in the Porsche box you need one oil for both diff and gearbox, so Mobilube PTX and Shell Transaxle are specially designed GL-5 oils that let both the diff and the synchromesh work properly.

Due to the above, the simple answer is to stick with the Mobil oil. I have however made my own oil mix now using an Ester based Motul oil and have added some Redline friction modifier.

[Paynewright]

Thanks. It doesnt have an LSD so thats one factor out of the equation! My other car specifically needs GL5 for the diff and GL4 for the gearbox so understand what you mean.

I’m struggling to find a supplier in the UK that sells 1 L bottles. My usual go-to oil source, Opie, doesnt seem to list them on their website.

Regards
Ian

[Paynewright]

So, my friend in the oil trade is struggling to find 1L bottles of either shell spirax S5 or mobil PTX transaxle oil. He can get the 20L drum at similar prices to what I can buy. So it seems I have the following options:-

1) Pay dealer price for 3L of the oil - £100+
2) Take it to my indi and let them do it + labour
3) Use the closest available spec, prob SHC - No LSD fitted
4) Buy 20L at circa £250 and sell off surplus


Any other suggestions?

Ian

[Gavc]

Reline Synthetic 75-90 GL5. i have this in and has made shifts a lot smoother and easier. I have also this in my Classic Ferrari which also has improved the shift and these are notorious for 2nd gear shift. Been using this product for many years. Speak with Opie Oils, if it helps I sell transmissions and engine for a living, so have a reasonable knowledge. But its your choice whatever you go with, at least you are looking to refresh which is a good thing

[Fastlane]

As said above, just ring Opie and ask to speak to Tim - is is Opieoilman on here. I met him last week as I live local to them.

[Paynewright]

Called Opie - they've suggested Motul 300 75/90.


I've used Redline MTL in my Caterham 6 speed box and many owners swear by it - I couldn't tell any difference between it and the recommended comma oil. I've also read one of the ford / caterham gearbox specialists advises against redline oils. There does seem to be lots written about oils and not much data based wear evidence of A) v's B).


Going to call my indy and see what he has to say.

Cheers

Ian

[Paynewright]

Indy just called back - any good quality 75/90 oil will be fine. Motul was mentioned so think I'll go with that.

Ian