here is what you asked for Mike
sorry just read the thread

 

Spec. data on each of the trans oil (from pdf data sheets via web):

Mobilube PTX (Porsche Spec.)
Viscosity at 40C, 77.2
Viscosity at 100C ,14.5
Viscosity Index, 197

Shell Helix 75W-90 (same as Porsche 999-917-546-00??)
Viscosity 40C, 81
Viscosity 100C, 14.9
Viscosity Index 194

Fuchs Titan Sintopoid 75W-90 (sold by Pelican Parts)
Viscosity at 40C, 90.5
Viscosity at 100C, 15.3
Viscosity Index 179

Mobil 1 Synthetic Gear Lubricant LS 75W-90 (retail product)
Viscosity at 40C, 99
Viscosity at 100C 15.2
Viscosity Index 142

Mobil Synthetic Delvac 75W-90
Viscosity at 40C, 120
Viscosity at 100C 15.9
Viscosity Index 140

All Viscosity in mm2/s

Appears that PTX and Shell are quite similar with Fuchs and retail Mobil 1 not matching the Porsche specs. Could assume that Shell Helix is the Porsche OEM in liter containers?

 

Its unfortunate George, that they do not list what aspect of the oil is different or special from any other.

 

Looking at the chart, the Mobil 1 looks to be thicker when cold, which could explain why it seems a bit "balky" when cold, but holds good viscosity at temps, when it could be important.

I think those numbers to paint a pic of what is going on. Although I guess I'd need to google Viscosity Index to see how that is defined.

 

thats mobil LS (parts store), not delvac.

 

Hey Gents,

I work in the commercial lubricants industry. You will never find the proprietary info on any of these products as they are closely guarded secrets. The big differences are in the additive packages and you would be amazed at the differences between different brands. All depends on where the product is positioned market wise and if the lubricant is intended to be an RFP fighter grade or not.

Also note Delvac was formally developed for class 8 over the road tractors and the associated industry bench tests ie Eaton Road Ranger, Voith, Allison etc very different from a P Car gear box.

Try some different brands until you find what works for your particular car or regular driving conditions.

 

I just ordered the Shell type from sunset (since the 20 liter restriction w the PTX). Doing the change this month. Will report back if I find it to be any different.

 

Just an update...
the tranny has always shifted smooth with only a slight mechanical / notch feel when cold in gears 1 & 2 for about the first 15 min.

the car has had delvac in it for at least 5 years, probably longer. decided to try something new, it was due for its 24 month change this month.

drained Delvac out along with a friend, we used gravity feed method with 5' x 3/4" clear tubing through the drivers side rear wheel well, and funnel to fill it up with 4qts of the Shell 75/90.

it was in the low 30's this morning and i took the car to breakfast, i feel like it might be a tiny bit less notchy 1 & 2 shift while cold. might be placebo effect, hardly noticeable. to sum it up, i think it feels the same as the Delvac

notes: both crush washers same as the one for the oil drain. torqued both plugs to 50nm. way easier and cleaner than doing an oil change.

 

Just wanted to add another “data point” to this thread.

Though I’m no stranger to Rennlist, I’ve been a long time lurker to the 993 forum; most of my contributions on Rennlist have been to the 930 forum.

I bought my 1995 C2 with LSD back in November 2013 with about 66K on the clock. The PO just had the car serviced, including a transaxle “gear oil” change at around 65K. The shop used Swepco 201. This was always my “go to” choice for annual transaxle service in my 930…always with excellent results. And while I’ve heard that Swepco is “okay” (it will work) in G50 boxes, it’s mostly associated with the G15 boxes.

My car is a daily driver. And my ownership thus far has been during the fall/winter months, here in Raleigh, NC. And while winters here can’t be compared to the Arctic, we get some temps in the teens, the twenties, and the thirties…especially in the mornings.

When cold, shifting could only be described as very slow, balky, notchy, clunky…even kludgy (am I making words up now). Things would improve once warmed up, but everything had to happen in very sloooow motion for a few miles. Even with the car off, clutch in, the shifter had a feel of resistance when moving back and forth in neutral. It felt stiff.

So with 70K on the clock, I was all set for the switch to Delvac. Then my local source for Mobile Delvac 75W90 stopped carrying it and instead began offering Mobile1 LS 75W90. So I went back to the drawing board and found this thread. I called my local dealer and they had plenty of the factory Porsche/Shell stuff (part # 999-917-546-00) in stock. I purchased 4 liters of the stuff at $37 per liter. My box took approximately 3.7 liters for the fill.

Instantly things improved. The shifter has a very slippery feel to it. I’m very careful with warm up procedures and am never hard on the car until it has come up to temperature, but the shifting, even when cold, can now only be described as more fluid. I’m very pleased with the results and will continue with the “factory fill”.

I know that this stuff per liter is nearly the cost of an entire gallon of the Delvac, but in the big picture it is negligible…especially for something that I plan to change annually…maybe every 1.5 years. Again, this is a daily driven street car that will never see track time under my ownership…YMMV.

 

I used Royal Purple in my 96 C2 tip cab since it was readily available at O'Rielly's and don't have any complaints with it.

 

+1 Thanks Mike J -

With 50k miles driven since making the G/50/21 gearbox swap back in 2001, it was time. So following suit the oil sourced was the Porsche/Shell/Sunset variety. Shift character has been uber smooth at most any temp's, with ease.