2003, 5.9 Overheats at 70mph
 

Ok, so I've noticed that if I stay below 70mph my truck will maintain a constant temperature of 200. If I get up to 70mph it will quickly heat up to 245 or bury itself into the red. When I slow back down to 65 the temp cools right back to 200 within a few minutes.

I have replaced the fan clutch. No luck.

What's next, any tips, anyone ever heard of such a thing? It's got me baffled..


-Hank

---AutoMerged DoublePost---

Just got back from a little trip around the block, no bubbles visible at the radiator cap while at 200 degrees.

-H

my guess posible head gasket my 08 did about the same have you checked your t stat and check ur over flow is it full and is rad full if your over flow is full i would say hg

Is the radiator plugged with dirt? This was a common problem with the second gen trucks.

Could also be a thermostat stuck part open...

I would focus on the the thermostat and radiator, at least until those are ruled out.

Does it also overheat in city traffic? Can you smell coolant inside the cab?

when your truck is starting to get hot crank the cab heat all the way up. If it is a HG or a bad radiator cap it will blow cool air.
If it blows hot air I would first blow out the radiator and intercooler. If problem persists I would change the thermestat