What are your must-do things on new-to-you gmt900?

[m1dn]

Just got myself 08 Yukon XL Denali with 130k miles, picking up in few weeks.

What are your must do recommendations when getting these used trucks?

I’m planning on going down regular oil change, filters and have shop check suspension.

Anything else i should include right away, such as tranny oil?
As far as I’ve read the 08 6.2 doesn’t have DoD, so won’t need to disable this.
What about fuel/oil treatment, anyone adds anything regularly? I liked to throw in some MMO on occasional fuel ups and oil changes on my older f150, not sure if it’s a good idea with 6.2 since it takes premium fuel?

 

[OR VietVet]

If you have no paperwork, IMO, do all fluids. diffs, transaxle, transmission, coolant, brake and power steering and oil change.

 

[diesel_dave]

Definitely check your brake fluid. Every other fluid in my 2007 looked brand new but the brake fluid looked like it was the same stuff the factory put in it way back in 2007. Brake fluid should not be dark green. The pedal feel improved substantially after flushing a few bottles of DOT 3 through.

 

[PatDTN]

Something odd I learned when I bought my '09 was that the cruise control didn't work because the secondary brake light switch for trailer brake lights was bad.

Also, the tires on mine were in poor condition and mismatched. When I tried to use the automatic 4 wheel drive selection the truck started bucking like crazy. If I'm not confused you should have AWD on your Yukon so if it's doing odd things check to see how well matched the tires and pressures are.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

Be sure to change ALL cooling hoses, including the 2 plastic Tees near the fire wall on the passengers side, even if they look good.

 

[diesel_dave]

Something odd I learned when I bought my '09 was that the cruise control didn't work because the secondary brake light switch for trailer brake lights was bad.

Also, the tires on mine were in poor condition and mismatched. When I tried to use the automatic 4 wheel drive selection the truck started bucking like crazy. If I'm not confused you should have AWD on your Yukon so if it's doing odd things check to see how well matched the tires and pressures are.

Yep this! My cruise also didn't work when I bought the truck. I was at a loss and saw that the brake switch might be the issue so I took the original one apart to see what was broken. It all looked completely fine so I cleaned it and put it back in. Still broken. Bought a new one on Amazon for $10 and that fixed it right up. Makes no sense to me but the new switch was the trick.

 

[me88]

Coolant (rust inhibitors) and brake fluid (moisture content) go bad with age.

I'd leave the power steering fluid alone unless you hear a little bit of noise when under load (turning wheel at standstill). When changing it, either flush it through the cooling line or replace the oil in the reservoir a couple of times to get as much new fluid in as possible.

The front differential has conventional oil in it which should be changed regularly (50k?), the rear differential has synthetic oil in it good for 150k miles if it is equipped with the G80 locking differential. Look at the glovebox sticker and search for G80.

Transmission and transfer case use ATF (Dexron 6) if I remember correctly, which should be changed every 50k miles. GM says the ATF can go up to 100k, but the list of exemptions is huge so that doesn't really apply to any real-world conditions.

 

[GO0BER]

Yep this! My cruise also didn't work when I bought the truck. I was at a loss and saw that the brake switch might be the issue so I took the original one apart to see what was broken. It all looked completely fine so I cleaned it and put it back in. Still broken. Bought a new one on Amazon for $10 and that fixed it right up. Makes no sense to me but the new switch was the trick.

Funny story... I bought an 08 2500 by accident.. thought I was getting a Denali (the ad stated Denali and the only 2 things to tell me otherwise was selectable 4 wheel drive and 8 lugs instead of 6)... When I realized I got a 2500 and I could use it to tow my 28 ft toy hauler I immediately grabbed a brake controller and put it in. Hooked up to my trailer and immediately had issues in which my trailer brakes were getting low voltage signal even when the brakes were not applied.. turns out my brake switch was bad.. I didn't even think about that affecting cruise control. I'll tell my wife she should have working CC.

 

[intheburbs]

If you have no paperwork, IMO, do all fluids. diffs, transaxle, transmission, coolant, brake and power steering and oil change.

Regardless of service history, unless maybe it was done recently at a dealership, I change all fluids when I buy used. 5 of the 6 vehicles in my sig were bought used, all around 70k-80k miles.

Engine oil, transmission, transfer case, coolant, and both axles. Brake and PS either left alone or changed on a case-by-case inspection, though on my 2500 the PS was an automatic fluid change because of hydroboost.

 

[mountie]

I should change out my differential & rear.... Everything else was changed after I got my '05 Yukon XL 5 years ago.