Overheating six
 

1994 F150 4.9L E4OD.
New hoses-belt-water pump-thermostat (looks like NAPA)-thermostat housing-rad cap (16 lb)-flushed. About 50 degrees F outside temperature, so it is nowhere near hot out. Old water pump leaked, less than premium flow (feeling the heater hoses, no heat), but the truck didn't overheat with old water pump-thermostat-hoses-cap.

After driving around for about 30 minutes, temp gauge goes up and stays up. Coolant boiling out of overflow tank. One time the 13 lb rad cap shot off, lost most of the coolant a mile from home. I figured when I lost heat in the cab I might have an issue.:-hair

Second NAPA thermostat, 16 lb rad cap, first drive over 30 minutes, still boiling over, erupting from overflow. Let it cool down 10 hrs (work), added good half gallon coolant, drove 30 minutes, temp gauge way up.
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Shut it down, boiling into overflow, but didn't spew out.

Probable thermostat, or other things to check? The gauge goes to "O" or "M" during the first few minutes like it should, fluctuates a bit in the normal range, then after 30 minutes or so, goes up and stays up. The top rad hose doesn't feel like there is much flow when the gauge is high. The coolant boiling out of the overflow tank is brownish. Previously quite a bit of stop-leak dumped in to cooling system, might still be some in the system to get boiled out. No bubbles in the filler neck when engine is running cold. Doesn't appear to be water/coolant in oil. Next thing to acquire is one of those funnels that attaches to rad neck, to bleed air out.

My feeling is the thermostat is still sticking closed after a while. Any other suggestions?

Check thermostat housing. If it is warped it will not allow the thermostat work properly. I would check the cap but if the coolant is coming out of the overflow the cap is working. Try a lower temp thermostat. And if it has had stop leak put in it I would pull the radiator and have it boiled/cleaned out. Have you checked your clutch fan ? In had a problem with my truck getting hot while driving around town and I changed the thermostat no difference I changed the clutch fan and voila now it runs ice cold

New thermostat housing, old one was pitted.

At this rate, a new radiator couldn't hurt. Perhaps heat-activated goop is still in there, clogging it up when it gets warm. The clutch fan has some resistance when moving it with engine off, doesn't freely spin.

Those funnels with the rad cap mounts seem to be hard to find, must keep looking.

I'd say you have a blown head gasket.

As Conanski pointed out, its starting to sound like blown head gasket. Good idea is to start truck and let it warm and check reservoir tank. If there are bubbles forming, then it's very likely it the head gasket. You could also do the coolant dye test that will show if exhaust is entering the cooling system.

Also, pull spark plug, anyone should due, just get that cylinder at TDC and hook up adapter to air compressor and start adding air. If the gasket is just shot, then it's a god chance that you could see bubbles forming in the radiator or overflow. Checking each cylinder for compression is a good start. I had a 302 that showed 140-150 on all cylinders, but using the air compressor method proved it was the head gaskets.

Should the fan suck your hand in when you stick it between the grille and condenser at idle? Just a faint breeze on mine.

Drove it seven miles with the rad cap on loose, parked it uphill, added a bit more coolant, trying to get any air out of the system. Idled fine for about a half hour, put the rad cap on tight, drove around the country block (40-55 mph), heated right up again. Shut it down, boiling out of the recovery tank again.

I'm guessing all the stop-leak that was in it might have been masking a bigger problem...:-down:(

My guess woukd be the rad. When I was having overheating problems it was my water pump, but I took out and flushed the rad really well. You wouldn't believe the amount of rust and sediment that was in the rad.

Keep us posted on your findings.

Replaced the thermostat with a Motorcraft one.

Motorcraft one on the left.
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Drove it around the country block. Heats up quicker, in-cab heat seems to come up quicker, gauge still goes up to the L in "Normal", maybe a little past. Didn't boil over out of the expansion tank when I shut it off, so that might be an improvement. Probably need to burp the system a little better. Also hearing some gurgling from the heater core area when it is hot. I might try bypassing that to see if it is causing issues.

Fan spins pretty freely after hot shutdown, I'm thinking that might be an issue. If I understand things, the clutch fan should be more locked up when hot. Definitely not hearing any sort of fan roar at any time.

What size hose goes from the rad to the expansion tank? Mine has a slight leak.

Your fan clutch is definitely shot. The radiator is very easy to remove and hose out. It's cheap and it might solve the problem before you throw any more parts at it.

If it's the head gasket, a compression tester will show that pretty readily.

The rad looks like it might have been replaced before. But with all the stop-leak in there... Fan clutch will be next. Not sure if I want to put a head gasket in, if that is the problem.

It's your fan clutch. Nearly 100% certain on this. I've had overheating problems with both F-Series vehicles & Mustangs in the past and the culprit has always without exception been the fan clutch.
When it's the water pump it is usually very obvious-loose feeling when pulling on it.
When it is the radiator you can tell by the obvious leaking.
T'stat can be tricky as you can't see it. But this is your fan clutch, trust me on this!


Roger

Hey Roger was your old man a TV repair man. I bet he had an ultimate set of tools for you to use. Lol

I'm gonna throw a wrench into the equation..

If theory proposes its the fan clutch, then as long the truck maintains a steady speed, then the air being pushed against the radiator and block, it should keep it cool and steady until you stop and sit idle.

How many revolutions can you turn the clutch fan after the engine has been driven long enough to warm up? I can only turn mine 1/4 turn maybe a hair more. I will say that if the water pump has been replaced, then it should dictate to replace fan clutch at same time, unless the water pump was just junk or defective. If you got 10+ years out of both and one fails, its served well and just replace to prevent later failure of the 2.

If you maintain a speed of at least 30-40 MPH while driving and the truck is still overheating, then the fan clutch, whether it's working the way it should or not, is not the problem.

Temp gauge stays up at 45-55 mph, country highways. I would think ram air at that speed should cool things down, but it doesn't.

Rad doesn't have any obvious leaks, but could be clogged up. Time to take it out and check it over.

The fan can be spun by hand maybe a turn or more when shut down hot. Not much resistance. The old water pump had a pinhole leak in the pipe that goes towards the heater, and I think the bearings were bad. Things are a bit quieter up front now.