Hey yall,
I got a 97 4x4offroad ext cab 4.6
And bout 4 months ago the heater started workin intermidantley it would be warm but not hot, when i had it on hot. But if i would switch it from cold to hot it would get hot and stay hot for a little while then start cooling off, and it got to the point where it stopped getting hot all together.
PitStop replaced the thermastat and it worked fine for about a week then started doin the same thing. Obviously im takin it back to pit stop to get them to straighten it out.
But is there any reason my truck would be burnin up thermostats??

 

Your thermostat was probably fine. Several problems give your symptoms, (1) low coolant, (2) air block in engine, (3) exhaust creating air block through head or head gasket, (4) water pump isn't always pumping. Good luck.

 

Coolant is fine,
Where would an air block be at? How would it affect anything? Are you referring to a blocked vaccum line some where? HOw do i check for a blockage?
Exhaust is flowing fine out the dual pipes, does that mean number 3 is out??

 

OK, I assume coolant is fine in the reservoir. When warm but not hot squeeze the upper radiator hose vigorously a few times to slosh coolant into and out of the reservoir, cap off. Watch your hand near the fan. See if you can 'feel' a low level in the radiator. If it 'feels' like it is full of water, the radiator is full. Lines between the radiator and overflow are sometimes blocked.

An air block is an air bubble in a head or more often in the intake manifold. They can interfere with the flow of coolant. They can prevent cooling of the heads. But they can also prevent the flow of coolant through the heater core. It has never been clear how, but it can.

By exhaust, I meant a leaking head gasket or cracked head leaking exhaust into the water jacket. This causes the same problems as an air bubble, in effect it creates an air bubble, and is one of the common symptoms of a bad head gasket. Symptoms are just what you described.

Water pump is just what it sounds like. One way a water pump can fail is for the impellers to slip on the shaft, doing nothing.

Filling the coolant on a car is easy and nearly foolproof. On some engines, air naturally gets trapped in the engine. Some engines have a place to bleed off an air bubble. My brother in law has a steep bank along his driveway and drives the car up it and fills them at a steep angle. I've pulled coolant sending units or ECTs to verify I didn't have an air block. I've had them on several engines, including my 4.2L in December after replacing the radiator. Nothing I did fixed it until I drained it and refilled it. Part voodoo.

 

I guess the first thing im gonna check will be the coolant, and squeezin the hose like you said. I was hopin to jus hear o its a loose wire goin to the thermostat.. I still do wanna check the connections to the thermostat. Is the thermostat near the throttle body? Can you tell me exactly wehre to find it? What does it look like?

 

The thermostat doesn't have any wires. It's still the old fashioned bimetal spring type. They don't fail often, I'd say they are rarely the cause of this problem. Sometimes they are but I'd suspect the afte all others I listed.

Some new (2004/2005) trucks have very high thermostats (220 degrees) and have an electric heater built into them so they will open for extra cooling under some conditions (no, I'm not making this up!). But yours doesn't.

Some people think that you can watch the temperature gauge in your truck and tell if the thermostat is working. But air bubbles and head gasket leaks cause the temperature guage to go down and the heater to blow cold even though the truck is overheating. When an air bubble is under the coolant sending unit, the sending unit measures the temperature of the intake manifold which is relatively cool.

If you haven't drained or been low of coolant since last winter, I'm guessing you don't have an air block (unless this happened last winter too). To tell if you have a head gasket leaking exhaust into the coolant, there is a test kit you can get at NAPA (or probably at your ford dealer). Assuming your coolant level is OK, I'd take it to a Ford dealer or a mechanically minded friend to determine the problem. But let us know. Good luck.

 

I squeezed the radiator hose with it runnin at full temp after drivin home form school. It looked like it took a second of squeezin before any ran into the overflow. So when its cool im guess im gonna take a look at the level and see if i need to add much. I can understand why this would be a problem. But I dont understand why it would be so intermitent. Sometimes i crank up drive it gets hot stays hot, but others it wont get hot and others it gets hot and cools down and gets hot ect....

 

Yeah, I've never understood that either. If you think that is hard to explain, some head gasket leaks have voodoo symptoms. Only when you step back and look at the overall pattern can you see it.