Getting ready to change the rear axle/differential oil in my 2003 GMC K2500HD truck, and I have a few questions.
Basically looking for oil brand recommendations. Manual says to use synthetic 75w90 GM P/N 12378261/ specification 9986115. Checked the local O'Reilly and the guy at the counter looked up my truck and GM P/N 88900401 is showing as a replacement for the numbers in my manual. Options available were the O'Reilly MasterPro, Royal Purple, Castrol, and Lucas Oil. I am leaning towards Lucas or Royal Purple, have heard good things about both. Any thoughts or experience on what brand to choose?
Other question is about having or using a limited slip additive. Truck has RPO code 'G80' which is for the locking differential. A bit confused as I see conflicting opinions on use of limited slip additive. Some say yes and others no. A search on the net turned up a GM Service Bulletin saying not to use a limited slip additive in the truck axles with RPO G80. I looked up the specs on the Royal Purple and it has the limited slip additive, and the Lucas oil does not. Not interested in Castrol, and the counter guy basically told me not to buy the MasterPro if I planned on keeping my truck for a while.
So it looks like Lucas Oil is the product I am looking for. Or is there another source/brand? I can go to the GM dealer and buy there. Specs I have show the differential holds 2.75 Quarts of fluid. Going to replace the cover gasket as well.
Any help would be appreciated.
Basically looking for oil brand recommendations. Manual says to use synthetic 75w90 GM P/N 12378261/ specification 9986115. Checked the local O'Reilly and the guy at the counter looked up my truck and GM P/N 88900401 is showing as a replacement for the numbers in my manual. Options available were the O'Reilly MasterPro, Royal Purple, Castrol, and Lucas Oil. I am leaning towards Lucas or Royal Purple, have heard good things about both. Any thoughts or experience on what brand to choose?
Other question is about having or using a limited slip additive. Truck has RPO code 'G80' which is for the locking differential. A bit confused as I see conflicting opinions on use of limited slip additive. Some say yes and others no. A search on the net turned up a GM Service Bulletin saying not to use a limited slip additive in the truck axles with RPO G80. I looked up the specs on the Royal Purple and it has the limited slip additive, and the Lucas oil does not. Not interested in Castrol, and the counter guy basically told me not to buy the MasterPro if I planned on keeping my truck for a while.
So it looks like Lucas Oil is the product I am looking for. Or is there another source/brand? I can go to the GM dealer and buy there. Specs I have show the differential holds 2.75 Quarts of fluid. Going to replace the cover gasket as well.
Any help would be appreciated.