Just got my truck back from the dealer and I noticed that the tech put 80W90 oil in the diff. I had it at the dealer to repair a leak and they removed the diff. cover and also replaced the pinion seal in the front. When I looked at my owner's manual, it clearly states 75W140 Synthetic high performance lube only and that approx. 4 ounces of friction modifier should also be added. Will this cause any damage???? I have been on the phone for the last 3 days trying to get them to do something. Any ideas???? Thanks....

 

Yes, it can cause damage if left as is. Totally unsat if the dealer is giving you a hard time. Talk to the service manager directly, and demand they drop the cover and put in the correct fluid with the proper amount of friction modifier. Then keep copies of both repair tickets in case the rear develops a problem.

 

If you definately have the LS, then you definately need the 4oz. of friction modifier (unless the replacement fluid contains these additives; some do). It's also advisable to use the proper lube that's specified in the long term. There is a tag attached under one of the rear end cover bolts that gives oil recommendations. When I have questions about service, I just go in and ask to speak to the service manager; everyone else just goes and asks them anyway.