I have a 2002 Quad Cab, 4.7 with 204,000. Twice in the last year it has overheated. Both times adding more coolant solved the immediate issue and I was unable to reproduce the overheating. Here are my observations:

Both times there was a very full overflow tank. I added coolant to the cap on the top hose from the radiator to the engine. I recently replaced the radiator and the fan clutch. There was no sign of coolant on the ground or under carriage.

I had noticed the last few weeks a smell coming from the engine when I parked. Not your typical engine smell but I could not place the smell until this weekend. I believe it was like steaming coolant smell.

I borrowed a pressure tester and tested the radiator cap (original cap) and it held pressure at 15 PSI but released at 20 PSI down to 11 PSI. I did a pressure check on a cold engine and it held 15 PSI for two plus minutes.

I warmed up the engine and did another pressure check. It would slowly drop from 15 PSI down to 11 PSI in about two minutes. I must have a small leak that I am guessing hits the exhaust and never drips to the ground.

With the radiator cap off, I start a cold engine and watch the coolant for movement. Once the thermostat opens I see coolant move towards the radiator. It slowly starts to rise up the neck of the radiator neck. Every 20 seconds or so I see 2-3 bubbles.

I removed excess coolant from the overflow tank so it reads halfway between full and empty. I read that high level of coolant could be a bad radiator cap, but this one tested good.

I decided to add some cooper stop leak to see if that stops the smell on a hot engine. I might try another pressure test after several cycles of running the truck. I will also watch the level of coolant in the overflow tank and if it rises I will try a new radiator cap.

Could I be missing anything else?

 

You just ruined the entire cooling system putting that copper stop leak stuff in.

 

Yeah. Never use stop leak.

Either you have an air pocket in the cooling system and need to burp it properly. Or you overheated and caused major damage, I.e...head gasket, cracked block, cracked head. Etc.

 

agreed. stop leak is bad juju. Best thing you could have done is keep it running with the cap off to burp it, ideally with a blower or something moving some air across the radiator to keep the water temp at 190-200.

 

The 4.7 is burped at the engine block by the coolant outlet into the rad.