you power washed from the inside out I hope. if you sprayed from the outside in, it buries the debris deeper into the fins.

get a "t" and back flush the whole cooling system. sounds like it still clogged.

how does the rad look?

you mentioned a new t stat was installed.

check the little heater hoses around the block for leaks.

replace the rad cap

do ya have a pic of the engine compartment??

 

Check for hairline or small cracks (something that won't leak unless there is more than normal pressure in the system). Especially the plastic tanks on the side of the radiator. Mine did exactly as you described and slowly got worse because the plastic tanks on the side were leaking. A local radiator shop replaced the tanks and flushed the radiator for $75 and it has worked fine ever since.

 

If you rule out the cooling system and have an auto trans, I would have it checked out. I had a '86 Feerd gasser that this happened to and it was the trans slipping when towing.

 

I concur with cowboy bob, check the rad tanks. look for ANY signs of seam failure. the left tank on my rad went out last friday. installed a new all steel 4 core rad unit and its runnin cooler than an eskimo on ice!

 

From everything I'm being told, I guess I should start with replacing the the Fan clutch and water pump. I really don't won't to pay dealer prices. Should the NAPA parts be fine for these??

Thanks

 

I have a 2010 2500 with the 6.7 with overheating problems also. I only
only have 2400 miles on it. They have replaced the fan clutch. It still runs from 199 to 208 back and forth while it is under any kind of load. It rus up to about 203 with no loadand backt0 199. Since Dodge does not know or wants to know what is wrong any ideas.