'07 GM 6.0L engine running up to 255 towing from 350 el up to 5.700 el

[Greaser007]

OK, so I've been towing a Toyhauler dry weight 5,400-lbs from 350 feet elev up to 5,700 feet elevation the last three summers.
There are three long hard pulls on this climb into the Sierra Nevada mountains on hwy 36 east out of Red Bluff, Calif.
The last three summers, the engine temps climb to 255 degrees F, necessitating down shifting into Low-gear to prevent overheating while chugging in Secon gear.
Our summer days can normally be 104 degrees, so I didn't think much of the situation. The Suburban 2500 has 3:73 gears and stock 245 -16 tires.
Ok _ _ _
Summer of 2025, we had the local Chevy dealer install a new radiator as the original began producing seepage from a split in the drivers side plastic tank.
We didn't pull the trailer in summer 2025 either.
So, _ _ _ just this last week, July 21st, we pulled the trailer up the merciless climb, and VOILA, _ _ _ the engine temps stayed steady at 210 degrees, and we chugged over the three summits in Second gear !
My Conclusion of why no high-engine temps this year:
I think my old radiator cooling fins were Plugged with Bugs.
The new for 2025 radiator with no bugs cooled the engine properly as it should.

 

[mikez71]

With a split in the radiator tank, it probably struggles to hold pressure, which would also lead to higher temps.

 

[strutaeng]

The bottom of the radiators will build up gunk and debris.

My 99 Silverado radiator with 265k (original) got swapped out when I did a 5.3 swap, and the bottom 4" maybe was blocked off with gunk. I took a photo, I'll see if I can find it...

Probably a good idea to pressure wash the radiators with some low pressure/high volume wash every few years. Kinda similar to home AC condensers working hard in the summer and sucking up debris, grass clippings and dust. Should power wash those periodically as well to maintain cooling efficiency...

 

[Marky Dissod]

My Conclusion of why no high-engine temps this year:
think my old radiator cooling fins were plugged with bugs.

With a split in the radiator tank, it struggles to hold pressure, which would also lead to higher temps.

Both.

Probably a good idea to pressure wash the radiators with some low pressure/high volume wash every few years.
Kinda similar to home AC condensers working hard in the summer and sucking up debris, grass clippings and dust.
Should power wash those periodically as well to maintain cooling efficiency ...

From back thru front for quicker results, otherwise you might be jamming debris deeper into fins.

 

[j91z28d1]

The bottom of the radiators will build up gunk and debris.

My 99 Silverado radiator with 265k (original) got swapped out when I did a 5.3 swap, and the bottom 4" maybe was blocked off with gunk. I took a photo, I'll see if I can find it...

Probably a good idea to pressure wash the radiators with some low pressure/high volume wash every few years. Kinda similar to home AC condensers working hard in the summer and sucking up debris, grass clippings and dust. Should power wash those periodically as well to maintain cooling efficiency...

you're right, I've popped the end tanks off a few old radiators and even if the fluid looks good, they are full of gunk in the bottom. very few people,flush the fluid every 5 years or so as they say to do. so the coolant can look good, but still not be.

 

[Marky Dissod]

My Conclusion of why no high-engine temps this year:
think my old radiator cooling fins were plugged with bugs.

With a split in the radiator tank, it struggles to hold pressure, which would also lead to higher temps.

Both.