I have a 99 with the 52 in it. This truck has been highly maintained through its entire entire life.
Anytime it’s absolutely needed anything. It’s always in. I owned it for eight years and the prior owner had a wet dream of paperwork that went with it.

Head gasket, etc. and heads have been rebuilt within the last 10,000 miles. Professional shop.

I drive this truck 2 to 3000 miles a year

I am running an aftermarket fan as I do tow with this vehicle quite often.

100% fan is working correctly. With a override

This fan runs so cool that the truck normally will hang around the quarter Mark.



Right at the normal mark when it’s towing.

But in the last few weeks, it has been overheating. It will run cool for about 10 to 25 minutes and then it will spike up to the point of boil over. this is intermittent, but it will run extremely hot to the point of boil over all the time now.

It’s starting to nickel and dime severely, and I refuse to take it into the shop again.

I’m thinking thermostat what’s your opinion?

 

Sounds like a stuck thermostat. You can check the temperature around the thermostat housing with a laser temperature gun from startup to boil over to see if the thermostat is indeed the culprit. The laser temperature guns are available at Harbor Freight and many other places..

Did you also get rid of the factory clutch fan setup with the install of the electric fan?

 

The thermostat is the first thing I'd check. A bit of a pain compared to older engines but not too bad. One caveat though, absolutely, positively do NOT put a fail safe thermostat in there. Just go with a normal range unit (usually 192 or 195) with a jiggle valve on it. This lets the air get out to keep it from air locking. Every single Fail Safe thermostat I've dealt with either had failed, or failed soon after. I had one fail the first time it warmed up.

You might be tempted to go with a cooler thermostat. Don't do it. It will make your fuel economy tank. The computer will go into "open loop" mode. This is where it injects extra fuel to warm the engine up in place of the choke on carbureted engines.

If the thermostat doesn't cure the problem, your water pump might have an issue like corroded impellers inside. I replaced one once that was older but looked decent. However, the previous owner hadn't kept the coolant fresh and the impellers were nearly gone completely.