Overheat Problem

76/79BroncoGuy · Sep 24, 2004

I just found this forum and think it's great. Like everyone else I seem to have my own problems.

I have a Stock 79 Bronco Trailer Special with a 400m. It's an automatic and has air conditioning. My problem is that whenever I'm caught in traffic the darn thing overheats. Its done this since I bought it.

Separately, I have replaced the heater core, radiator, fan, water pump, two radiator caps (currently tested at 13psi), three thermostats (recently tested and at factory specs), new temp sending unit, tested the gauge, had the system flushed, and two days ago I adjusted the timing.

Don't know if it's related, but my heater doesn't always put out really hot air.

Its not a built truck. No lift or any engine performance upgrades. Even have the fan shroud in place.

Does anyone have any advice or suggestions?

Broncoholics · Sep 24, 2004

It sounds to me that you have an air bubble in the motor.
If there is air, you will not get much heat in the heater. Do you have an overflow for the radiator to pull back some water when it cools? When its cool is the water level in the radiator full? Can you see the water moving in the radiator once the thermostat opens?

If its ok on the freeway, do you have a fan shroud?
At slow speeds the fan can't pull enough heet out of the radiator without a shroud.

I use Wetter Water made by Red Line stocked at any part store. It reduces the engine temp by 10 deg.

You can always add vents or a hood scoop to the hooda and cut out the wheel wells for more flow. Wrap the exhaust with heat wrap (drops the engine compartment temp by 70%).
Maybe an oil cooler would help but it doesn't sound like the problem.

4xfan78 · Sep 24, 2004

You said that you replaced the radiator, did you go back with the 4 core(or flue) radiator ( this was the stock item in a trailer special) if not this could be one problem. The other is you replaced the fan did you put a fan on with a clutch or without a clutch(prefered fan for most). what degree t'stat is in it, and where do you live. The other thing is when you fill the radiator when the truck is running.

Broncoholics · Sep 24, 2004

It just hit me, I bet the fan was put on backwards. Check by getting a piece of paper and see if it sticks to the front of the radiator while running. That would make perfect sence why it would run cooler on freeway VS. stand still.
Let me know...

4xfan78 · Sep 24, 2004

broncoholics that is a good one that would cause that problem. I can say that is one thing that I have never done(knock on wood) I have made almost every other mistake though. Let us know if thats the problem.

DragonDave · Sep 25, 2004

Fan Clutch?

4xfan78 · Sep 25, 2004

On 78 and newer trucks ford put a clutch (big silver thing that bolts between the fan and water pump) on they work good when they work and are exspensive to replace. Don't know of any advantages but I am sure somebody else here does or could explain it better.

BigNasty · Sep 26, 2004

two radiator caps (currently tested at 13psi),

Is that the correct cap that's called for?
Mine runs a 16 lb cap.
If it is too small, then it will blow out and overheat the engine quickly.

But what sounds to me like your biggest problem is traffic.
Everything with a standard fan will tend to get hot while in stop and go traffic, usually quite quickly as the heat put out from all the other cars along with the lack of air flow (air being forced through the radiator, as if the vehicle was moving) adds up, especially if running the A/C while sitting in traffic.

Do you have an actual temp gauge or an idiot light on the truck? (either can give a false reading) I have seen idiot lights come on way too soon and guages that read hot while actual temp is fine, doesn't happen too often, but does happen.

As for the heater not putting out warm air, that could be the fan or the duct flappers.
If the fan is working, I would check to see if the duct flaps actually change over when you turn the temp up. OR, since I am not positive that Ford didn't go the route Chevy went, there may be a heater controller under the hood that has gone bad. It basically keeps water flow out of the heater core until you turn on the heater. If the truck has one of those, it may be bad also but use caution if the truck is warmed up as I had one of the GM heater control valves blow up in my face one day when I stared at it too hard.. then poked it just a tad

Seabronc · Sep 27, 2004

Do both of these problems happen at the same time?

Not putting out heat sounds like a vapor lockin the water system. I think you would have the Ford system that pumps water thru the core all the time, one of those Better Ideas by Ford

, PITA, I know my 83 does. That means that hot water cycles thru the core even in the summer

. Sorry, just a little rant

.

In any event, if your mixer door is in the warm area, and you don't get heat, it ain't pumping water thru the coil :angry: or your blower ain't blowing.

Overheating in traffic, like BigN says, is common. Possible solutions;

Electric fan, larger radiator, Transmission oil cooler (automatic), Engine oil cooler.

I have an oversized radiator and transmission oil cooler, and am considering the electric fan (couple more horsepower available to wheels, and better air flow when in traffic). If I were towing, I'd consider putting on an engine oil cooler from a F250 or E250.

I didn't install the radiator, it was there when I got the truck, but I did install the transmission oil cooler, that in itself keeps my water temp down well in the low end. The temp only got to mid scale once this summer when I was setting in a bank line while the teller was checking with the President and FBI for anyone that wanted some of their money back B) .

Good luck,

>-

Broncoholics · Sep 27, 2004

If you have a clutch fan it could be bad (not spinning fast enough at idle). Check to see how easy it is to turn the fan by hand. it will move easy if it has a clutch fan and will be ridgid with standard fan. Now start up the motor and see it it gets up to speed at idle. Clutch fans give the motor slightly more power. As the engine revs up the clutch slips slightly so it doesn't rob the engine of its power. Basically it takes power to turn the fan thus robbing horsepower.

76/79BroncoGuy · Sep 29, 2004

Thanks for all the responses. My job requires me to be out of town for several days at a time. This is the first time Ive had a chance to respond. I have a bunch of ideas to try.

Both problems do happen at the same time. I have already installed a flex fan and the fan shroud is on. The cap is supposed to be at 13psi.

Ill double check the fan direction. I dont have an overflow tank but the fluid level doesnt change either. I can see movement in the radiator when the thermostat opens. The radiator is new and supposed to be the same. Ill double check to see if it is really a four core. I bought a thermometer to check the actual temp the next time it overheats. I suppose the gauge could be grounding when it gets to a certain temp. The transmission oil cooler is a great idea. Ill have to look into that too.

As for my heater problem everything works correctly. When the temp fades, I can swap the hoses going into the heater core (which is also new) and I get hot air again. In about a week the hot air fades back to warm. It's starting to sound like air in the system.

If I have an air bubble in the cooling system, how do I get rid of it?

Broncoholics · Oct 1, 2004

Usually the air bubble will go away if you have an overflow bottle to pull back water when it cools. You could try parking on a hill with the front of the truck up high and fill the radiator. You might have to pull one of the hoses and make sure the block is full.
I found that my thermostat didn't open enough and had to drill a small hole.
Once up to temp, feel the temp of the upper radiator hose with your hand. Then feel the bottom radiator hose and see if its the same temp. If not the thermostat isn't opening all the way. You might try an earlier opening degree like 175. Or take it completely out for a few days and see if it makes a difference.

Guest · Oct 2, 2004

Thanks for all the great ideas. At the moment, I'm thinking I have a serious air bubble in the system. I'm out of town again for a few days. I let you know what happens when I get the chance to tinker with it.

Seabronc · Oct 3, 2004

One way to get air out of the heater core is to put a flush T in the return line and crack it slightly while the engine is running. Water is pumped thru the heater core even when the thermastat is not open. Doing it this way, you don't have to deal with hot coolant.

Good luck,

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