Told to drain my differential fluid

I changed the gearbox/diff oil in my 07 CS manual last week and used Liquid-Moly GL5 , 75W-90 Fully synthetic hypoid gear oil. It's one of the fluids listed on Pelican Parts and FCP Euro as compatible along with Porsche , Motul and Fuchs. I emailed Liquid-moly to ask a question about using ceratec in the diff and the guy told me the ceratec is fine but Liqui-Moly doesn't make a gear oil for the Cayman S manual and I should change it immediately. That doesn't seem right but this is someone from Liquid-moly saying this. If it's the same number as Porsche (000-043-305-49) and Fuchs and Motul , the Liqui-moly should be fine also right? I have driven the car and it seems fine, shifts nicely. Should I be doing what he says and replacing the fluid? Is the transaxle picky on the Cayman ? Thanks

Several years ago a contact at Guard Transmissions recommended only using Porsche transmission fluid in the manual transmissions on the 987. He noted that the synchros used in the transmission are unique to the 987 and not many fluids are compatible with them. He also recommended shorter change intervals than factory recommendations, especially If you drive them harder. I’d drain the fluid and get the Porsche fluid.

I'm using Motul do to a Wavetrac LSD preference to this 75-90 gear lube. Seems to work fine. I need to change it though after 30k miles.

Worthwhile reading: https://bobistheoilguy.com/forums/threads/difference-between-gl-4-gl-5.102015/ Basic summary - due to the increased loading of hypoid gears used in differentials GL5 was developed with additive packages that prevented breakdown of the oil film between the two gear surfaces in contact. Unfortunately some of the additive packages (I seem to recall sulphur being the bad one) would cause yellow-metal corrosion. Synchronizer rings are made of "yellow-metal" (I believe a bronze alloy) and some of these oils were notorious for destroying the gearbox synchronizers, so.. GL4 was suggested. Another one that popped up explaining the difference: https://toolinggeek.com/can-you-use-gl-5-gear-oil-instead-of-gl4/ I'd go with what Porsche recommends, especially since the oil manufacturer told you to get it out of the transmission ASAP.

I ordered the Porsche Fluid. The Liqui-moly guy said he would contact Pelican Parts and FCP Euro to tell them that oil is not to be used in the Cayman . I still find it hard to believe it’s fine for the 996 and 997 but not the Cayman . Better safe than sorry I guess.

I changed the fluid in my 09 C manual with Delvac 75W-90 synthetic. Does this have the same risk as the Moly? Should I be changing this out with the Porsche fluid?

Was the Delvac a GL4 or GL5 oil? Or GL4-5? If there is a 5 in the oil description it doesn't belong in the gearbox. This page has some info: https://www.mobil.com/en/lubricants...ts/for-businesses/heavy-duty-lubricants/products/mobil-delvac-1-gear-oil-75w-90 Considering that warning, and a later note in the specifications that it exceeds GL5 specs - IMHO - it doesn't belong in your transmission.

Thanks - much appreciated. I've had it in the gearbox for about 2,500 miles. How might a GL-4 fluid affect my transmission?

A GL4 fluid shouldn't affect the transmission at all. It's the GL5 we're concerned with, and if you've read the posts above you'll know the answer on what the concern with GL5 is.

Thanks - did the reading and spoke to my local parts dept. Sounds like the Porsche fluid is 999.917.546.00, which I can get from Suncoast for $39 / L.

Schnell Autosports: Schnell Autosports Gear Oil – 1L (SAE 75W-90) OEM, Genuine & Aftermarket Parts | Performance + Racing | Accessories $20.60 (Titan oil) Pelican Parts: Pelican Parts Search: "999.917.546.00" - $50.00 SMC: SAE 75W-90 Gear Oil, 1 Liter (97-13) - Titan Oil - $17.19 ECS Tuning: https://www.ecstuning.com/b-genuine-porsche-parts/transmission-oil-fro/00004330504/ - $75.95 FCP-Euro: Gear Oil 75W90 (1 Liter) - Genuine Porsche 00004330549 - $32.39 Based on these results - easily found by just googling the Porsche part# - if Schnell Autosports or SMC has it in stock (they claim to) - that's where I'd be ordering it from. Of course you can also order Porsche labeled oil directly from the dealer, but the dealer price seems just a tad inflated (and they'll probably have to order it in - they normally keep oils in 50 gallon drums for the shop.) FWIW - Porsche doesn't make oil. Usual engineering practice would be to use something already available, not to require inventing a new oil to suit the application unless the application is new and unique (which this isn't - German transaxles go back to 1939 in the original VW Peoples-Car. EDIT: I'm eliminating anything except the factory fluid - on the advice of Fuchs/Titan Oil in Germany: Lubricant advisor And if you're ordering from FCP-Euro (my parts vendor of choice - they're very good) - I'd call first and confirm that they have the oil and that it's the correct oil for the car. Many Euro parts sites are showing that oil as discontinued.

Pretty much what I said in my earlier post, Porsche fluid only recommended in the 987 Manual Transmission. Why risk it with anything else for something that doesn’t cost that much more? As far as the explanation why the 987 isn’t the same as the 997 or 986 , it is a different transmission entirely and if I remember correctly different suppliers. I wish I could post more details but I kept all that information in my ******** account which I no longer have access too.

The 987 uses a Getrag 6-speed, the 997 uses an Aisin .

Pelican Parts lists the Porsche fluid as well as that from LiquiMoly , Titan/Fuchs, and Motul as having part number 000-043-305-49. But according to Liquimoly , even though the numbers match, only the Porsche fluid works in the 987.

Maybe? I dunno. The Getrag 466 is used in other cars and Porsche isn't making gear oil, so there's got to be some other fluids that are fine. One would just need the spec. The Porsche fluid works fine in the 5-speed and Aisin 6-speed so it can't be some magic unique elixir, I think. Personally I'd guess it's GL5 spec given that it needs to protect the differential: the yellow metal corrosion issues for GL5 are moot given that modern transmissions generally don't use brass or copper synchronizers.

I checked and Suncoast sells the PTX 75W-90 for cars through 2012. So that's probably the manufacturer of the Porsche fluid (which, again, is spec'd for all the cars they make) and Mobil says it's specifically designed for the 911 transaxle. It's GL4 and GL5 spec'd. Mobil 1 Mobilube PTX 75W-90 Check out the deal on Mobil 1 Mobilube PTX 75W-90 at Suncoast Porsche Parts & Accessories www.suncoastparts.com PdsDetailsPage Mobilube PTX is a SAE 75W-90 multipurpose gear lubricant. It has been developed to provide outstanding performance specifically in Porsche 911 transaxles. www.mobil.com If I had to guess, the main difference in this stuff would be that they left out the LSD friction modifiers that are in many gear oils. In a transaxle car the oil is shared by the transmission and diff, and the friction modifiers can make the oil too slick for the synchronizers to work well. That may be why Liqui Moly doesn't recommend their synthetic stuff.