Best oil for manual transmission

[my996]

I read the DIY to replace the manual transmission fluid. Loren, which fluid do you recommend? – Here is what I have seen so far…

http://www.autobarn.net/luc10047.html

and

http://store.avlube.com/mob1syngearo.html

Also, other than the motor oil for the crank case and the manual transmission oil, is there any other oil I need to replace?

[Loren]

For street driving and occasional track use I would stay with the Mobil PTX. You won't need 12 quarts you will only need slightly under 3 liters.

You will also want to change the gear oil in the front wheel drive on your car (4 liters of ATF). I will try to get a DIY online here in the next couple of days - it's not too hard.

[umn]

Hi,

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.

Cheers,

Uwe

[my996]

For street driving and occasional track use I would stay with the Mobil PTX.  You won't need 12 quarts you will only need slightly under 3 liters.

You will also want to change the gear oil in the front wheel drive on your car (4 liters of ATF). I will try to get a DIY online here in the next couple of days - it's not too hard.

<{POST_SNAPBACK}>

Ok Mobil PTX it is for the transmission. Will that cover it for the rear diff too? BTW, ATF for the front? - - Is that right?

[Loren]

Yes, gear oil for manual transmissions and rear differential. ATF for the front wheel drive.

[my996]

Does the manual transmission and rear differential have seperate drain and fill holes or are they the same?

[Loren]

Same.

[my996]

I would stay with the Mobil PTX. 

<{POST_SNAPBACK}>

Any idea where I can get this Mobil PTX?? Thanks

[Loren]

Well, if you don't want to pay the dealer then I would use the Mobil 1 75W-90 synthetic gear oil.

Dealer prices:

000 043 204 20 Mobil PTX - 20 liters (retail $550.32)

999 917 546 00 Shell Transaxle - 1 liter (retail $29.57)

Mobil 1 75W-90 synthetic gear oil street prices:

3 quarts - $25

[umn]

Well, if you don't want to pay the dealer then I would use the Mobil 1 75W-90 synthetic gear oil.

...

I don't think I would. For the reasons explained above (gearbox and diff in the same casing and hence using the same oil), I'd use a transaxle-specific oil.

Almost all major oil manufacturers make them, Mobil 1 calls it PTX, Shell calls it Transaxle, Castrol calls it TAF-X. There is a reason why Porsche (or in fact GETRAG) recommend a specific oil.

Obviously you can pour in whatever you want, but if you knowingly discard the manufacturer's advice, then don't complain if your gearbox (and in particular the synchromesh) doesn't last as long as you might have hoped.

Also, I wouldn't necessarily go with people's recommendations "ABC is a good oil for Porsche boxes". Very few people understand the specifics of gearboxes, not even car manufacturers themselves (they just buy them in) and certainly not the mechanic at the dealership. But why not just go with the gearbox manufacturer's recommendation and be on the safe side?

Cheers,

Uwe

PS: I know that the old G50-bases boxes used any old 75W-90 API GL5, but the synchro was different and the change intervals were shorter.

Edited May 24, 2005 by umn

[my996]

Thanks Uwe. I do plan on using what Porsche recommends. Now I am just trying to find out where to get it. If only the Dealership has it, then I will get it from them. :)

[Loren]

Well, if you don't want to pay the dealer then I would use the Mobil 1 75W-90 synthetic gear oil.

...

I don't think I would. For the reasons explained above (gearbox and diff in the same casing and hence using the same oil), I'd use a transaxle-specific oil.

Almost all major oil manufacturers make them, Mobil 1 calls it PTX, Shell calls it Transaxle, Castrol calls it TAF-X. There is a reason why Porsche (or in fact GETRAG) recommend a specific oil.

Obviously you can pour in whatever you want, but if you knowingly discard the manufacturer's advice, then don't complain if your gearbox (and in particular the synchromesh) doesn't last as long as you might have hoped.

Also, I wouldn't necessarily go with people's recommendations "ABC is a good oil for Porsche boxes". Very few people understand the specifics of gearboxes, not even car manufacturers themselves (they just buy them in) and certainly not the mechanic at the dealership. But why not just go with the gearbox manufacturer's recommendation and be on the safe side?

Cheers,

Uwe

PS: I know that the old G50-bases boxes used any old 75W-90 API GL5, but the synchro was different and the change intervals were shorter.

Mobilube PTX is not sold in th US - except by Porsche dealers at a 5X markup.

Mobil's Specs:

Mobilube PTX (synthetic) 75W-90 GL-4, GL-5

Mobilube 1 SCH (synthetic) 75W-90 GL-5,PG-1,PG-2

[umn]

...

Mobilube PTX is not sold in th US - except by Porsche dealers at a 5X markup.

Mobil's Specs:

Mobilube PTX (synthetic) 75W-90 GL-4, GL-5

Mobilube 1 SCH (synthetic) 75W-90 GL-5,PG-1,PG-2

...

:oops: Altough you had said it earlier on, I didn't realise that PTX isn't sold in the US. I was thinking why the h*ll do they want to use a different oil?

From the specs you can't tell if Mobilube SHC is OK, the specification GL-5 alone is far too general. There are quite a few different GL-5 oils around, particularly for different kinds of LSDs (limited slip diffs), with varying amounts of EP additives and friction modifiers. You definitely don't want a high EP content in your gearbox oil.

However, I had a look at the spec sheet on

Mobilube 1 SHC 75W-90

and concerning the EP content, they say "where mild extreme pressure gear lubricants are recommended". It also looks like it is specifically designed to work in the gearbox and differential: "Wide multipurpose capability: One lubricant for heavy duty manual transmissions and rear axles".

AFAIK Mobilube is still developed in Hamburg/Germany. If I've got time I might give them a quick call tomorrow and see what they say.

Cheers,

Uwe

Edited May 24, 2005 by umn

[my996]

Seems as if I can get a hold of the Shell recommended product. However, (and not to question Loren's recommendation) the Porsche dealer stated that the same Shell transaxle oil goes into the front diff too. The dealer tech seemed concerned when I said that I would be putting ATF into the front diff. Loren - are you sure on your info? - I value your opinion and do not want to put the wrong fluid in by mistake. Thanks.

[Loren]

Seems as if I can get a hold of the Shell recommended product.  However, (and not to question Loren's recommendation) the Porsche dealer stated that the same Shell transaxle oil goes into the front diff too.  The dealer tech seemed concerned when I said that I would be putting ATF into the front diff.  Loren - are you sure on your info? - I value your opinion and do not want to put the wrong fluid in by mistake.  Thanks.

I have never done this on a C4. I quoted you what the service manual says (see below). The service manual could be wrong - the easiest way to tell for sure is to take the fill plug out and stick your finger inside to touch the oil. If it comes out with a red colored very light oil then it is ATF if it comes out with a thicker yellow/brown oil then it is gear oil. Please let us know if the service manual is wrong!

[Loren]

I found a second source (AllData) and they say gear oil too. Makes sense to me - I think the service manual is wrong. I will correct the DIY page.

[umn]

...

Please let us know if the service manual is wrong!

...

I'd say it is wrong. If you look at the TSB on transmission oils, it says "Transmission oil SAE 75W-90 for manual transmission, front-axle drive (C4), and rear axle final drive (Tiptronic transmission)".

Cheers,

Uwe

Edited May 24, 2005 by umn

[my996]

Checked it out. The front diff is gear oil, not ATF.

[my996]

BTW - an update - I purchased the Porsche gear oil from Sunset Porsche in Oregon. Cheapest by far, same product as all others. Here's their link. http://www.sunsetimports.com/porscheparts.php

[teeerex]

We have the same issues in the UK with regards to getting hold of any of these 'recommended' oils.

I've found out that Silkolene make an alternative (race derived so may be superior and is fully synthetic) :-

Silkolene Silktran SYN 5

API GL4/5 75W/90

Which matches the Porsche specification perfectly - and is definately a Transaxle oil.

I got mine from a UK distributor for £8.99 per 1L vs Porsche's £15.00 per 1L so cheaper too ! Also fantastic service from them with next day delivery.

PM me if you want details ...

Cheers,

Richard.

[mrpcar]

FWIW

I contacted Sunsetimports Porsche to order the gear oil and this is their response to me.

From: JeffClark@sunsetimports.com

You would use the liter versions 999-917-546-00 and the trans uses

almost 3 liters, front diff says 1.5 liters. Problem is I can't ship

it, hazardous material. We sometimes ship one or two in one box but more

than that too much possibility for damage. Get it from your dealer is

the best way. It's sae 75-90 weight but probably Porsche only. Jeff.

Edited December 22, 2005 by mrpcar

[viper501]

I just replaced mine w/ the B.G. full syn gear oil. The difference is incredible. Synchros definitely seem happier.

[SPR]

FWIW I have done the change before with the regular mobile 1 off the shelf from the local auto store. It is extremely hard to shift while cold.

I then went to the auto gallery and they are the ones who sold me the castrol which makes it shift like butter all the way around. However recently after about 15k it seems like the fluid has broken down or something, and the syncros are not being engaged as easily- i.e. maybe too slippery, but dunno.

I think I am therefore going to go back and get the oem part numbered fluid and go from there. BTW the castrol pictured that they sold me was what they gave me when I asked for gt3 tranny fluid. I asked for this because I have a limited slip. After talking with Jeff at sunset the gt3 and 996's run the same part number fluid FWIW. Loren also my tranny for whatever reason maybe becasue of the limited slip seems to use more fluid than a normal 996 and about the same as a gt3 maybe? I thought the increase in gt3 fluid was due to the tranny cooler though. In any event, back to stock stuff for me. Hopefully nothing bad has occured from the castrol. :)

[GaryFB]

Seems as if I can get a hold of the Shell recommended product.  However, (and not to question Loren's recommendation) the Porsche dealer stated that the same Shell transaxle oil goes into the front diff too.  The dealer tech seemed concerned when I said that I would be putting ATF into the front diff.  Loren - are you sure on your info? - I value your opinion and do not want to put the wrong fluid in by mistake.  Thanks.

<{POST_SNAPBACK}>

I have never done this on a C4. I quoted you what the service manual says (see below). The service manual could be wrong - the easiest way to tell for sure is to take the fill plug out and stick your finger inside to touch the oil. If it comes out with a red colored very light oil then it is ATF if it comes out with a thicker yellow/brown oil then it is gear oil. Please let us know if the service manual is wrong!

Hi Loren; I think the Workshop Manual proceedure may also be incorrect on the capacity of 9 liters for the front drive differential. Maybe 9 liters of ATF for the entire tiptronic.

[mrpcar]

Is the Shell MTX the same thing as the Shell transaxle? I can't seem to find the Shell transaxle on their web site at all.

Edited February 28, 2006 by mrpcar