Epic road trip after action report - high-mileage 2500, 35-foot trailer, in the Rockies

[intheburbs]

Teasers... I'll post more once I get back in front of a computer.

2008 2500 with 255k miles
Zero mechanical issues encountered
5,000 miles driven in 16 days
35-foot, 8,000-lb trailer
Multiple Continental Divide crossings including Powder River Pass (9,666') and the Eisenhower Tunnel (11,100')
50+ miles of moderate to severe offroading in 1 day - almost needing a spotter.
2 instances (brain farts) of driving 100+ miles in 4wd on dry pavement at 70+ MPH
Max trans temp achieved - 233°
Max engine temp - ~240°
28% oil life left after first 2800 miles (started at 100%)
6.6 MPG average westbound (altitude gains and wind)
7.6 MPG average eastbound
A crazy u-turn in Idaho Springs (IYKYK)
Mornings with no wind I could tow in 5th at 65-70, 2500 RPM (about 25% of the time)
Once we hit wind or hills, 4th gear and 3300-3400 RPM (75% of the time)
Probably the most abuse I've ever heaped on this truck.

 

[Marky Dissod]

Max trans temp achieved - 233°F (111.67°C)
Max engine temp - ~240°F (115.56°C)

Anything over 221F / 105C, I start getting nervous.
@ 230F / 110C I start looking for a spot to pull over.
NEVER want to see motor oil or ATF temps reach 239F / 115C ever again.
But that's just me.

 

[intheburbs]

Anything over 221F / 105C, I start getting nervous.
@ 230F / 110C I start looking for a spot to pull over.
NEVER want to see motor oil or ATF temps reach 239F / 115C ever again.
But that's just me.

As you should be, with a GMT800 running Dex3.

Luckily for me, the GMT900 trucks use Dex6, which is a substantial improvement over Dex3, especially in heat stability.

I've had my 6L90 hotter than that many times. Still original, still shifts/performs flawlessly.

 

[rzabel]

Sounds like a great trip. I've traveled a lot through the Rockies too, mostly Montana, Colorado and Utah. You might be interested in my Mexico road trip:

Epic Mexico Eclipse Road Trip

Just returned from a 6 week road trip pulling a 1948 Spartan Manor travel trailer with my 2003 Yukon XL with 219k miles (started with 214k). We started in Oregon and watched the total eclipse in Durango, Mexico. The drive from Mazatlan to Durango on the "Espinazo del Diablo" (Devil's Backbone)...

www.tahoeyukonforum.com

I probably should have posted it in this forum anyway, as I have a 2003 GMC Yukon XL 2500. With the 8.1 and 4L85E I never saw temps above 210F. My gas mileage was similar. My trailer only weighs about 6,000 lbs though.

 

[Marky Dissod]

As you should be, with a GMT800 running Dex3.

Dex3 my @$$.
I switched to Dex6 in my Caprice 9C1-LT1 the day Dex6 came out.
My Z71 has LubeGard's version of Dex6 in it since 6 months after I bought it.

And I see no harm in enthusiastically avoiding 239F.

 

[intheburbs]

Dex3 my @$$.
I switched to Dex6 in my Caprice 9C1-LT1 the day Dex6 came out.
My Z71 has LubeGard's version of Dex6 in it since 6 months after I bought it.

And I see no harm in enthusiastically avoiding 239F.

Doesn't change the fact that other components in your transmission don't deal as well with heat. The 6L transmissions were designed for normal operating temperatures of 190-200°. And the "trans hot idle engine" warning triggers around 262°. My all-time high is 243°.

Plus, there's an easy fix - replace the fluid more frequently when running it hard.

 

[Marky Dissod]

May I change the subject a bit, since I'm staunchly dead set against any fluid temps over 239F?

What axle(s) gear is your 2500?
Do you have - and/or recommend - a fan on your ATF cooler?

 

[intheburbs]

May I change the subject a bit, since I'm staunchly dead set against any fluid temps over 239F?

What axle(s) gear is your 2500?
Do you have - and/or recommend - a fan on your ATF cooler?

3.73 gears
No fan on trans cooler.
Truck is completely stock - suspension, engine, wheels, tires. Only a Blackbear tune.
The only times I've hit 240 are, IMHO, the "worst-case scenario" - towing at max GCW (16,000 lbs), steep grades (7% and higher), and thin air (altitude over 9,000 ft).

A good friend of mine used to work for GM as a transmission validation engineer. His first project when he was hired was 6L80/6L90 validation. When I told him about my trips, he said, "We did much worse during validation."

 

[RTCburb]

Great report..... and I like your truck! I have an '07 version.

I could hazard a guess where your u-turn was. If you're talking Idaho Springs, CO. It's one of my regular night stops on my way further out west to see my kids. In fact I'll be there in about a month & 1/2.

 

[Fless]

Great report..... and I like your truck! I have an '07 version.

I could hazard a guess where your u-turn was. If you're talking Idaho Springs, CO. It's one of my regular night stops on my way further out west to see my kids. In fact I'll be there in about a month & 1/2.

Remember when Idaho Springs had a free RV tank dump right there on the north side of Colorado Blvd in the middle of town? A buddy of mine used that just about every time when going through with his trailer. Kind of an interesting location for a dump.