Help with Correct/Recommended Fluid for Rear Differential Fluid (2023)

[McDermut]

Good afternoon All,

I'm hoping to do a "Quick and Dirty" gear oil change on my rear differential, which will involve using a pump run through the fill hole down into the differential to siphon out the old oil and then reverse the process with fresh oil. I'm well aware this is only doing half the job and I should replace the gasket, clean the magnet and so forth, however from what I've researched this is a good way to at least replace a majority of the old oil, and unfortunately, I am pressed for time and tools before I'm driving over 500 miles across the state towing a 1,400 lb camper for a couple of days. I don't know when the rear diff oil was last changed, it could have been a long time and a couple dozen thousand miles at least, and I want to mitigate as much as possible the risk of destroying my diff on this trip.

I've included pics of my RPO codes and a couple of my diff, I was hoping for some suggestions on what brands/types of oil I could use and y'all recommended. My RPO lists the GT4 and G80 codes, and the manual recommends SAE 80W-90 and to not add friction modifier. From what I've read on this forum the additive is generally not recommended for this type of diff. Also, is filling the diff until oil starts to leak out the fill hole an acceptable and sound practice? I was also wanting to see if anyone had gone through this process before and if they had any issues or tips. I greatly appreciate any help and advice y'all can give.

 

[OR VietVet]

In the pics, I see no leaks, so therefore I would say that what you have planned will be ok. Use exactly what is recommended and when you start to see fluid come out of the fill hole, it is full. Put the plug in and good to go. The only difference is that if you do not remove the cover, you cannot clean old fluid out and cannot check for any debris that may be in there.

 

[Eman85]

Pull the cover, it's simple. A tube of sealer and you can clean out the housing and magnet. Most any brand of fluid will be fine, synthetic if you like. When filling I try to get it just below the hole checking with a piece of coat hanger wire bent in an L. If you overfill let it run for a few minutes. As far as differential goes it won't even notice pulling 1400lbs, carrying it in the back would make a difference.

 

[McDermut]

In the pics, I see no leaks, so therefore I would say that what you have planned will be ok. Use exactly what is recommended and when you start to see fluid come out of the fill hole, it is full. Put the plug in and good to go. The only difference is that if you do not remove the cover, you cannot clean old fluid out and cannot check for any debris that may be in there.

Pull the cover, it's simple. A tube of sealer and you can clean out the housing and magnet. Most any brand of fluid will be fine, synthetic if you like. When filling I try to get it just below the hole checking with a piece of coat hanger wire bent in an L. If you overfill let it run for a few minutes. As far as differential goes it won't even notice pulling 1400lbs, carrying it in the back would make a difference.

Thank you both very much for the information and advice, it doesn't please me that I cannot do the job completely but I want to do what I can now, at least whatever crawling under my car in an apartment parking lot can accomplish. I found that Lucas offers an 80W-90 gear oil, but doesn't seem to specifically list my diff type as exceeding the service level. Would this be a good option to use, or am I having a "blown fuse" moment and overlooking a better option?

https://www.oreillyauto.com/detail/...v/a/27171/automotive-suv-1999-gmc-yukon?pos=0

 

[wjburken]

I tell ya, I just did the differential fluid on my F-150 and Autozone had Valvoline full synthetic gear oil in pouch-like containers like apple sauce packets they make for kids. Not sure if any other manufacturer have gone this route or not. That made it so much easier to get the fluid into the differential. No need to pump out of a bottle, just stick the tip in and squeeze like a tube of toothpaste.

 

[YukonGTmaster]

This is what I use. Right from the GM parts counter.

 

[Hoesgottaeat2]

Don't overthink it! Some folks go a lifetime with never changing the gear oil and are ok. But regular interval changes will help with peace of mind I say. Like any other engine lubricant, keeping it full is most important. And cleaner is always better.