Differential Gear Oil

[duzie]

I happen to stop by the local Ford parts store and asked them for a couple qts of 75W-90 weight non-synthetic gear oil and he said all Fords use Full=synthetic gear oil (XU-75W140-QL). He wondered why we were using the Non-synthetic gear oil. Could some one explain the difference to me?

Thanks for you help,

Duzie/Guthrie OK MK4 F5R1007406RD

[Scott Zackowski]

Duzie,

I am not sure why the FFR manual recommends non-synthetic oil. On my Mk4 build, I am using the FFR Moser 8.8 Differential in a 3-Link setup and it came with a sticker on it stating "Synthetic Lube Only".

In theory, synthetic oil should withstand heat better and last longer. It is more expensive! Many new vehicles come with all synthetic oil and lubes. It should not matter that much which ever one you choose.

My local BMW mechanic states that once you use synthetic, you have to stay synthetic, but you can switch from non-synthetic to synthetic at any time.

Some people believe that non-synthetic soaks into new metal better and better to start with. I have not been able to confirm that. In addition, it seems not to make sense since many new cars like Vettes. BMW's are delivered with only synthetic oils lubes.

Scott in NC
Mk4 F5R1007304RD

[duzie]

Scott,

My FFR Moser 8.8 Differential also came with a sticker on it stating "Synthetic Lube Only". I plan on following the instruction on the sticker.

Cheers,

Duzie/Guthrie, OK

[Bill_VA]

Would you still use the Friction Modifier with synthetic lube?

[CDXXVII]

I put a call into Moser about my 8.8 Moser 3 link and the Moser tech stated that he recommends non-synthetic 80W90 gear oil with a Ford specific friction modifier. I originally wanted to use synthetic oil but was having a hard time finding 80W90 gear oil in synthetic. I am getting a lot of mixed messages about this. Would be nice to get a factory techs input on this.

[Jason Lavigne]

Hey guys - for anyone reading this thread, there was another similar one where it was confirmed that the recommendation is non-synthetic oil with the Ford-specific friction modifier. Here's a copy of the text from some of the last posts on the other thread:

"Just spoke to technical support at Moser earlier this week to address the gear oil issue. He stated that synthetic was not recommended and that the ideal oil is a non synthetic 80W90 with a Friction Modifier. He also stated that the Friction Modifier needs to meet the Ford factory specifications. I ended up purchasing 80W90 StaLube brand gear oil with the StaLube Friction Modifier. We will see how things work out. "

"8.8 Solid Rear Axle - ( 3 Link )
Oil Type Capacity - 80W-90 1.875 qts.
Friction Modifier - 4 oz.

I just filled mine with a non synthetic gear oil by Sta-Lube with the Sta-Lube friction modifier ( Meets Ford Specs. )"

Hope that helps,

- Jason @ FFR

[RGHarvey]

Jason,

Thanks for the clarification. It's hard to keep track of all the related threads!

Bob

[Glory Bound]

I am using Royal Purple gear oil in my 8.8. Should I also use friction modifier? If so, which one?