F-150 overheating with no coolant loss?

This has been driving me nuts for months now. 93' 5.0 F-150. The coolant keeps leaving and the truck overheats. I have changed t-stat (twice), New cap, new hoses last year, flushed radiator (though it could still be clogged).

Fan belt seems OK, fan blades seem OK. Will run fine for a day or two after refilling but within maybe 4 -5 days and 300 miles will overheat again. During that time gauge movement indicated t-stat working properly. Coolant always low when it overheats. No visible leak from anywhere. Empties coolant overflow tank after 4-5 days of normal use. No water in oil. No vapor visible in exhaust. Runs fine otherwise. Heater is hot.A/C is always off (doesn't work and compressor clutch is spinning freely so doesn't seem to be taking any HP)



My guesses are down to

1. Blown head gasket (though with no visible leak, no water in oil, and no cloud in exhaust, I am skeptical. Only time I ever had that happen to me years ago it looked like I was fogging for mosquitoes out the tailpipe)

2. Bad fan clutch- clutch slipping badly at higher speed (No idea how to check - seems fine.)

3. Clogged Radiator - handles load at idle but at highway speeds not enough surface working? Boil off water slowly over 4 -5 days until it just can't handle any load?



I do not want to invest much in this truck - 180,000 miles, but I can't see junking it for something as simple as overheating.F-150 overheating with no coolant loss?
A friend of mine had a problem like this with his Accra (@ 110K miles no less - %26quot;good%26quot; cars?). Turned out to be his head gasket. Another indicator is it started to overheat while idling -- cooled down at speed. Nothing from the tail pipe. I would suggest running a compression test of each cylinder.



I had another friend who blew her engine on a 2005 GM Tahoe because of a blocked radiator even though she had the dealer do all the maintenance. It failed during a freeway trip up north, overheated during freeway speeds. It occurred during a long mild uphill grade with her fully packed SUV.



Those two will help you diagnose your problem, in both instanced the cars started to overheat -- during idle, blown head gasket; during freeway driving under load, blocked radiator.



This should help you.F-150 overheating with no coolant loss?
Can give any reference, but years of experience says you have covered all the possibilities.F-150 overheating with no coolant loss?
If it is low on coolant then there is definitely a leak. It is either going right out of the exhaust via a cracked port in the head, its leaking on the ground and you're not seeing it, or its leaking under the dash and you have a heater core problem. It's important to remember that a head problem doesn't mean that there will definitely be coolant in the oil. Check the passenger side floor mat for moisture. If it's wet then you have a heater core problem. F-150 overheating with no coolant loss?
take a coolant pressure tester and pressure up the entire coolant system to 15 to 16 psi this will make the system act as if it was at temperature while cold you can locate you leak or where it is pushing the water while doing this check your oil see if coolant is leaking to there also pull all the plugs see if you are getting coolant lose into the cylinders F-150 overheating with no coolant loss?
The guys above are correct, although I would take the radiator in to have it rodded out. If you take the truck in to have it smog, they can tell you if it is leaking fluid into the engine. You won't see the smoke coming out the tail pipe because you are moving away from the smoke at high speed.



Good luck!