What could cause my truck to overheat?

Hi there, it’s been a while since I’ve posted anything but I’ve been lurking in the background for quite some time.

Hope everyone is doing well.

My question is: what could be some of the causes of a truck overheating?

The truck in question is a 1985 Ford F250, 2 wheel drive, V8 5.8 liter Windsor.
New water pump.
Old radiator but clean inside and circulates water very well.
No thermostat; a thermostat seems to make it worse.
New cap, 12lb release.
No water in oil / oil in water.

It overheats after about 5 miles.
Any thoughts on what it might be?

All opinions and wisecracks are gratefully accepted.

Are you sure it’s over heating? Could you have a bad temperature sensor? I believe you can check that with an Ohm Meter.

Yep, it’s overheating all right.
Usually quite dramatically.

Once the temp gague hits about half way (about 5 miles into any trip) pressing on the gas causes an audible hiss under the sound of the engine.
I have deduced this to be steam escaping from the overflow.
At this point I probably have another 5 miles before it stalls out.
At any time between 5 and 10 miles, If I stop the truck and kill the engine, the radiator purges itself like a runway model.
Usually I’ll stick around there for a while, top off the 2 gallons of fluid (water or coolant, both act exactly the same except water is cheaper) and be on my merry way for another 5 - 10 miles.
Lather - Rinse - Repeat.

Sometimes, if it’s not very hot outside (or if it’s raining) I can stretch it out to 10 - 20 miles as long as I don’t stop and idle anywhere but past 20 miles it’s doomed regardless of the weather.

Anti-freeze raises the boiling point of the coolant. This means the engine can get warmer before the coolant turns to steam and escapes.
While this probably isn’t the problem, using water only probably isn’t helping either.

I assume nothing’s blocking the radiator (leaves, cardboard etc).

Do you get hot air in the cabin when you turn the heat on?

Dead water pump?

I dismissed that at first because I read

as the OP saying that everything was working well. I re-read and realized I read it wrong. “New Water Pump” doesn’t mean “working water pump” and “Circulates water well” could mean “I hooked a garden hose up to it and water went though it, then I installed it” as opposed to what I read it as…when is what I’m going to ask the OP to do…

OP, wait for the engine to be totally cold, take the radiator cap off and start the engine. Can you see coolant moving around (normally, you’d have to wait for the t-stat to open, but you don’t have one, so it should start right away)? You should be able to see it circulating.

Also, this is related to my above question about getting heat in the cabin. No heat inside could be a bad pump or a blocked radiator/heater hose.

The radiator’s clear of obstruction.
It’s a new water pump and pushes the water out like a fire hose when disconnected.
I get hot air in the cab; sometimes I’ll leave the heater on and the blower on high to squeeze out a couple more miles before the geiser.

It “uses” oil about like any other older vehicle - about a quart every 2 - 3 weeks.

I don’t know the oil pressure (the gauge always points to low), could poor oil distribution cause overheating like this?

Bad head gasket.

Does it have a radiator fan? Does it run?
If you’ve been regularly overheating the truck, I can’t imagine that the engine block is in very good shape right now.

The clutch on the fan may be bad and even though it looks like it is turnng it is not turning fast enough.

We used to just look at the fan when while the car was running, then turn the engine off. If the fan turned more than two or three revs we would replace it.

Are the radiator hoses collapsed?

There are failures where the pump impeller is so eroded that it does not pump enough volume. They don’t always get inspected close enough on a rebuild. If you run out of other items to check and it is a rebuilt pump, that deserves a look.

PS. The outlet hose from the radiator to the pump should be noticeably colder than the hot incoming hose.

Thank you all for the replies.


I get home from work this evening and decide to mess around with it.
I open up the radiator cap and add water.
It runs out of the bottom.

“This looks bad.” I say.

I crawl underneath it and the water is coming out of a freeze plug behind the starter.

“OK, I can handle this.”

I get a new freeze plug and replace it. Pour water in and it pours out again.

This time from the seam where the oil pan bolts onto the block.

There is a wad of black, sticky, crunchy gunk kind of like a mix of tar / lacquer / silicone.

My guess - this is the remains of a generation of various radiator stop leaks oozing out of what is most likely a cracked block. The winter freeze that pushed out the plug also pushed out all of the sealant that was holding the thing together.

Again thank you all for the replies but I believe the poor thing is a goner.
Nothing left to do but find the title and call the scrap yard.


something is blocking the flow of water through the engine. Since the thermostat has been removed then take the hose off the top of the radiator and see if you can readily blow air backwards through the engine. It’s a Windsor so the intake feeds water through the heads and then down through the block. Of course, you don’t want to be drinking radiator fluid so take care doing this.

Was something done recently to the engine that involved removing the heads or intake or possibly the addition of stop leak? I’ve seen gasket material turn to goo when subjected to radiator fluid. If too much was applied then the stuff that squirted out around a water passage would travel to the smallest point.

come to think of it, you just replaced the water pump. What did you use to seal it?

I used blue rtv sealant on the water pump, and a very thin film at that.

This might be your problem. Your coolant is actually moving too fast through the radiator to be sufficiently cooled. A thermostat does more than control the temperature of the coolant, it also controls the rate of flow of coolant through the radiator. At a minimum, reinstall the thermostat with the center removed, this should slow down the coolant enough for your radiator to do it’s job.

This is 100% incorrect.
The faster the fluid moves through the radiator, the more it’s cooled. If this wasn’t true, one would need a thermostat that closed as the temperature increased, which is clearly not the case.

I guess I failed that part when I took my ASE exam and aced it. You are wrong. The coolant in the engine block attracts the heat and carries it to the radiator where the heat is transferred to the radiator, the heat is carried away by the airflow through the fins. If the coolant moves too fast through the radiator for the proper transfer of heat to the radiator, the coolant get hotter and hotter. The primary purpose of a thermostat is to allow the engine to get to the correct operating temperature quicker. The thermostat stays closed till this happens. It’s secondary purpose is to control the flow of coolant in the entire coolant system. If the coolant moves too fast you also can get cavitation. This causes air bubbles in the coolant system and is a recipe for over heating.


Because I can give you plenty that you’re wrong:

From here: http://www.stewartcomponents.com/tech_tips/Tech_Tips_3.htm


From here: http://en.wikipedia.org/wiki/Radiator_(engine_cooling)


From a very long discussion here: http://www.eng-tips.com/viewthread.cfm?qid=262583&page=1