Over heating

[Bill Ran]

Good morning, I have a rd688s w/ 400 18 speed. The truck overheats when pulling hills loaded in 80 degree weather trucks warning light comes on and shuts down. It doesn't spew our fluid and just touches the red in gauge. I've changed clutch fan, idler, thermostat, and belts. Fluid is full we've pressure tested and no drop in pressure. I've washed out fins on radiator, ac, and charge cool. I've blown out with compressed air also. I'm thinking the water pump impeller may be corroded and falling apart. Truck has 300k on it. Thanks

[Joey Mack]

did you confirm the high temp using an I.R. thermometer on the water manifold? it will show a temp that is a little lower, but may show an obvious temp. issue, like a bad sensor saying its 210 degrees when it is actually 180ish..

[Geoff Weeks]

In all my time working on heavy stuff, I've had ONE impeller in the water pump be a problem. ONE wrong waterpump and countless radiator failures. 

If you want to go with the odds and not confirm with a test, replacing the radiator is the most likely solution.

If you want 100% confirmation, put a temp gauge in the lower radiator (return) and compare to the one on the engine. If the return isn't 10 deg cooler when working the engine hard, then you have proof it is the radiator.

Edit:

 The above is on a clean system that has been maintained and has a coolant filter that has been serviced at normal intervals. 

If you have never serviced or don't run a coolant filter, then all bets are off.

Edited 28 minutes ago by Geoff Weeks

[Brocky]

I drove a 78 Frtlnr with a big cam one 350 in it. The owner only used the local tap water plus anti freeze init with no water filter.. Had an overheating problem pulling hills. That water with NO additives had eaten the fins right off the water pump. In the process he also learned his cause of cracked liners!!!