Is it or Royal Purple considered much better than the standard porsche stuff?

 

Personal preference.

 

Reading these posts it doesn't seem uncommon on a modern 911, especially if you have a SSK as I do.

http://www.pistonheads.com/gassing/topic.asp?t=1067413

http://www.pistonheads.com/gassing/topic.asp?t=1554288

 

75/90 top brands are fairly indistinguishable i would imagine. i used redline 75/90 for years.

but once i installed an lsd its important to have gear oil without "friction modifiers' and for that, delvac is indeed the choice of most.

 

OP, when you say Porsche fluid do you mean the work was done at a Porsche Dealer? Or was it done by an indy with what they consider to be Porsche "approved" fluid?

I know many are having excellent results with various gear oils like Delvac, Red Line, etc..so I'm not trying to change anyones mind Just going to share the info I found. I have heard it mentioned a few times from folks running gear oils other than the Porsche approved ones that they have to be a little careful shifting when cold and then once warmed up all is great.

I spent some hours doing research on this recently since I'm getting ready to do my trans & diff fluids. There are only 2 "approved" gear oils by Porsche and they are:

1) Mobilube PTX
2) Shell Spirax S5 ATE (formerly known as Shell Transaxle)

As far as I know these are the only 2. There is no approved list with a bunch of different options, just these two.

I am not a lubricant engineer!!! just looking at the numbers to see if there are any consistent differences between the two approved Porsche fluids and all the others.

If you take a look below you will see that the approved fluids (Mobilube PTX and Spirax S5 ATE) both have almost identical numbers BUT the other 3 as well as just about all the other 75/90's out there have HIGHER Kinematic Viscosity (cSt) numbers AND LOWER Viscosity Index numbers. Could these differences be why some folks running the non-approved gear oils have to be a little more careful when cold? Good question!!!

Mobil MOBILUBE PTX 75W-90 (Porsche approved)
Viscosity
cSt @ 40º C 77.6
cSt @ 100ºC 14.5
Viscosity Index 195
Flash Point, ºC 226
Pour Point, ºC -60
Density kg/m3 849

Shell Spirax S5 ATE 75W-90 (Porsche approved)
SAE J 306 75W-90 SAE Viscosity Grade
cSt @40 81
cSt @100 14.9
Viscosity Index 194
ISO 9262 35000 Dynamic Viscosity mPa s
0 3 ISO 12185 879 Density @15 C kg/m
0 ISO 2592 205 Flash Point (COC) C



Mobil Delvac 1 Gear Oil 75W-90
SAE Grade 75W-90
Viscosity, ASTM D 445
cSt @ 40ºC 120
cSt @ 100ºC 15.9
Viscosity Index 140
Pour Point, ºC, ASTM D 97 -48
Flash Point, ºC, ASTM D 92 205
Density @ 15ºC kg/l, ASTM D 4052 0.86

Redline 75W90 NS GL-5 Gear Oil
Vis @ 40°C, cSt 94.5
Vis @ 100°C, cSt 15.6
Viscosity Index 176
Pour Point, °C -45
Pour Point, °F -49
Brookfield Viscosity @ -40°C, Poise 400 @-40°C

 

Thanks for sharing that. The fluid was bought by my specialist from Porsche directly. I've. Sen driving it today and it seems fine. I just think the guy wasn't used to the short shift which is a little more notchy than standard. When 'on it' you can change gears really quickly. May look into the 997 GT3 shifter mechanism.