Mobilube 75W90 vs Mobilube 75W90 FM for a Porsche PDK.

[Blinkerfluid]

I have a parts catalog that specifies different part numbers with different desctiptions for the PDK gearbox fill (not the clutch fill).

They are:

• 000-043-204-20 Mobilube 75W-90 PTX FM
• 000-043-210-12 Mobilube 75W-90 PTX

These parts are also specified for the front differential on AWD cars, but neither part has the "FM" in the description.
The FM stands for "friction modifier". Is there supposed to be something extra added to the oil for the transmission fill?

Ive talked to different dealerships. Some say the 204-20 part number is superceeded by the 210-12. Some are still selling it under the 204-20. None know what FM means. I saw a diagram listing these separately for the 918 trans/front diff fill.

Any input on what to do here?

 

[4WD]

Summit Racing sells lots of Mobil Delvac 1 75W-90 synthetic to the Porsche crowd … It’s reasonably priced and a great lube … Have seen it discussed on owner sites - or a call to Summit might help …

 

[RooflessVW]

I assume the FM is "friction modified" for cars with a limited slip differential.

Mobil Delvac works well in the manual transmissions but I have no experience with the PDK.

 

[kschachn]

So what did you decide to do with the other problem you posted today Blinker?

 

[Blinkerfluid]

So what did you decide to do with the other problem you posted today Blinker?

haha. This post is me second guessing everything we did now.

Just decided to throughly drain the fluid out and refill with the mobilube. I’ll do another drain and fill in 200 miles or so just to get the last little bit out.

 

[kschachn]

haha. This post is me second guessing everything we did now.

Just decided to throughly drain the fluid out and refill with the mobilube. I’ll do another drain and fill in 200 miles or so just to get the last little bit out.

I wouldn't have touched that expensive car without exact information from the FSM and/or owner's manual.

 

[Blinkerfluid]

I wouldn't have touched that expensive car without exact information from the FSM and/or owner's manual.

Yep. I had it. Just a mistake. They happen.
Actually this is my first ever real **** up in years of working in cars. I really wish it was on my old truck instead of this car.

On the other hand. I have had Porsche dealers mess up service before. It’s rare, but mistakes happen.

 

[Crispy]

I have a related question that I think is appropriate here. I just sold my 2007 987 Cayman base with a 5 speed. It had 225,000 miles and I had changed the gearbox oil at 32,000 with Mobil Delvac 75w90. The gearbox has been flawless. I just bought a 2015 981 Cayman PDK with 30k and want to treat it the same way. I see the recommendation is Mobilube PTX 75w90. Reviewing the spec sheets for these two, they are very similar except for the lower temperature viscosity. I live in northern NY and will be winter driving.
My question- That Mobil Delvac worked VERY WELL for me. I am hesitant to steer away from a Porsche recommendation but wondered if the reason for developing the PTX might be fuel economy related rather than performance related. Comments anyone? Thanks, C.