Hello,

I see on the forums here that the red line full synthetic 75w90 hypoid oil recommended for the diff. It also looks like others are recommending this for the 6 speed manual transmission as well? Or am I reading this wrong.

Doing some research Pennzoil platinum and ultra Platinum oils are made from group 4 and group 5 synthetic base oils vs most full synthetic are based on varying amounts of group 3 base oils.

​​​​​​As long as the oil is 75w90 and contains friction modifiers for the diff I intend to use the Pennzoil.

However here is my question. I see that most hypoid limited slip diff oils specifically state DO NOT USE in syncromesh transmission??? Yet it appears in certain threads the redline oil is recommended for both?

 

For the diff, I used 75W90 Fully Synthetic Hypoid Gear Oil (1 Liter) - Liqui Moly LM22090.

 

Yes I think my issue and what was confusing me, I confused two different red line oils. I thought that they were recommending the same for both. But redline actually recommended their gl-4 75w90 "mt-90" for the manual. And their 75w90 gl-5 or redline 75w90 gear oil. Two very different red line oils... Which I had confused as the same.

So I am considering using the Pennzoil synthetic 75w90 gl-5 full synthetic in the diff. And Mannol 75w80 mtf-4 in the trans as it meets MB 235.10 specs. Both which are quite inexpensive yet the quality is very high.

 

Let me add to the confusion! LOL
For the differential I used Redline 75W85. When I did the 6 speed transmission I used Mercedes-Benz Gear Oil MB 235.10.

 

Most sources say GL-5 fluids are "too slippery" for the synchros in a manual transmission. Redline fluids with the -NS are synchro friendly.

 

Do not drain diff or tranny until you can break loose the fill plugs. I replaced the 6spd oil with Pennzoil® Synchromesh, seemed like it helped a little with 1st to 2nd gear shifting

 

According to what I read the gl-5 fluids are a NO-NO for syncromesh. There are soft metals in the syncromesh that the aggressive friction modifiers in gl-5 can corrode and damage. Yet the gl-4 syncromesh fluids do not provide the superior shear protection that a gl-5 for our limited slip diff oil provides.

That's why I was so confused when I thought people were using the same in both. It appears that any full synthetic gl-4 fluid is good for the 6 speed manual. And any FULL SYNTHETIC GL-5 for our limited slip diff.

Those two specs as long as full synthetic should properly lube and take care of our cars. In a pinch oil is better than no oil... Just make sure you put the proper fluids in soon.

 

OEM differentials on all Crossfires are open; They are not "limited slip"