Fluids: Changed in Yukon XL

One advantage of my wife teaching in the vocational schools (3 different high schools) is, I bought all the fluids her Yukon has, and the auto shop teacher supervised while the students change the front differential, rear differential, transfer case, brake fluid, and the coolant. I did the motor oil last weekend as she had 12,000 miles on Mobil 1 synthetic and that is too many miles for my liking. I wanted the teacher to drain the transmission fluid, but he said at 90,000 miles he thought it would do more harm to change it than to leave the fluid in it. I normally do the service myself, but with 18.5 quarts of coolant and the shop having the tool to flush the brake system out, I thought why not let them do it. The week before they did a front wheel alignment which took the play out of her steering wheel.
Now my wife tells me that it is time to shop for a new Yukon or Suburban. Women!!!

I put the ol Presidential Mode of Transportation into TSTC, Texas Sate Technical College, in Waco years back when my brother worked there. They rebuilt the air conditioner in it for $90. I wish we had one closer( closest one I know of is in Sweetwater) and I'd let them replace all the fluids and shocks in my wifes Expedition.
When we were shopping for her a vehicle she agreed to keep the Expy fro at least a decade. So far she is still insistent she likes it so much she will.

This is the last week of school, but I have been tempted to have her drive my Silverado in on Thursday and Friday and see if they can change my oil, front differential, and transfer case. Easy enough for me to do but if they are willing, I wont need to lay on the ground and use a creeper. I still have 4 sets of stitches in my stomach so I am leery to do it this week.

I got an upgrade on a rental and was able to take a 2016 suburban for a 7 days. We drove it cross country and overall it was nicer than I expected. It was the long version, plenty of storage space, all black - looked like a secret service vehicle. It had 360 degree collision alert.

With 90K I'd change the trans fluid. I'm assuming it's not severely burnt and the trans shifts ok?

12K miles on Mobil1 is way to far, IMO. The standard "synthetic" mobil1 is not a PAO or group V based lubricant. IIRC there is/was a lawsuit against them somewhere and they can't call it "full" synthetic since it's not PAO base stock or group V.

I could be mistaken since I didn't sleep at a holiday Inn express last night.

The transmission fluid is not burnt. I'm on the fence about draining it as I have heard that too many people who never changed it out have problems with the transmission after doing so. With the Yukon, I don't think we will own it much longer, but one never knows for sure. I have 65000 on my Silverado, haven't changed the trans fluid yet but hope to do it this summer. I liked my Allison trans in the DMax as I could just use the drain plug and change out the spin on trans filter. I hate to take the pan down to change the transmission fluid and I don't want it flushed by a machine.

I normally change the oil at 7000 to 7500 miles, and I agree 12K miles was too long. Her Yukon uses 1 quart around 1000 to 1500 miles (dealer lied said that is normal). In that 12K miles 6 quarts of oil were added. Another reason to get rid of the Yukon. The Mobil 1 bottle states advanced fully synthetic oil Dexos approved by GM, and is a PAO base. There was a law suit, but it was Mobil 1 suing Castrol claiming Castrol was not pure synthetic. Castrol won, and result show Castrol to be the better of the oil. I may switch to Castrol after reading up on the subject more. I did have the Mobil Extended oil filter, I can't seem to find the non Extended filter.

TheQuig wrote:

There was a law suit, but it was Mobil 1 suing Castrol claiming Castrol was not pure synthetic. Castrol won, and result show Castrol to be the better of the oil. I may switch to Castrol after reading up on the subject more.

Good to know, thanks for looking into that.

As it turns out, the last 5 quarts that went into the Yukon on the 12K miles were the Mobil 1 Extended mileage oil 15K. I didn't give it much thought as it was the 1 time my wife stopped and bought the 5 quart jug on her way to Georgia.
I have a small notebook that goes back to 1990 with all work done on every vehicle I have owned since then. It doesn't make sense that I let her oil go so long without changing. I'm thinking there is a chance that I did a quick change before she left on a trip and didn't record the oil change. Her change oil light came on 3 weeks before I had the time to do it. Seven months and 12K miles seem like a lot of miles in a short time.
She has been making the Georgia trip at least 4 times a year, a lot of miles quick, I think when school starts up again in the fall, we will buy a new or newer Suburban.