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I have a 2009 Silverado 3500 HD duramax. When the truck was new I pulled our 14,000 pound fifth wheel through Eisenhower Tunnel (11,000+ feet). The engine and transmission both overheated on the way up. The high temperature lights did not come on. No problem since with overheating. Most towing is on flat land with one trip west each year. Is this normal Any modifications to avoid nonoccurence?
 

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Overheating, per se, can be different to different people. Some think that 225* is overheating, some don't. My experience, and I've been up thru Eisenhower several times with my 5th wheel, is that you need to keep your rev's up to say 2000 to 2500 which means speed in the neighborhood of 50MPH, probably 4th gear. This is no race course and the faster you go, the more heat you will be created in the engine. If you are building lots of power, you are producing lots of heat, so back off the power. Wind direction, if coming from the rear, can have an effect also, so keep it in mind. And air at Eisenhower altitude is much less dense than at, say, 5000 ft, so doesn't cool your truck as well.



At some point in the rising temp situation, your fan clutch should lock up and the engine temp should start coming down fairly rapidly. Your stock 15 lb pressure cap adds another 45* to the 223* boiling point of 50/50 mix of antifreeze plus water. So if you can monitor your temps (not with the factory gauge - something different) and the temps do not spike beyond 245* actual, you should be OK. One of the easiest ways to increase your safety zone for temps is to use a 20# radiator cap which adds about another 15* to your boil point. All this ASSUMES you have a clean cooling stack so that the air reaching your fan clutch is not diverted around the clutch by a mass of dirt, feathers, trash, etc. You MUST have a clean cooling stack.
 

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My 2008 showed this symptom. Pulling 14K 5th wheel, all fine and good until long grades. Then engine and tranny temps rising to the point I got DIC warning on engine temp. Get on flat ground and they dropped to normal fairly quick. Never heard the fan clutch engage at any time.

Finally pulled the stack apart. The main radiator was COMPLETELY full of junk. Amazed it could cool at all.

Cleaned the trash away, and now the temp gauge looks painted in place, regardless of load or grade.
 
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