1977 Highboy
 

I am haveing problems with my truck over heating. I have changed the water pump and thermostat and checked the whole cooling system. Does anyone have any suggestions?

Any recent body/suspension lift done on top of the OEM lift? If it had one as I haven't seen a HIGHBOY in eons since they were rare to begine with, is the lower air dam still in place? Either of these will affect the air flow under the vehicle causing the "LOW PRESSURE" area under the engine compartment to be eliminated. This in turn causes the air not to flow thru the radiator and out under the engine/body area like it should.

no new lift or anything like that it is mostly stock and im not sure what the lower air dam is, so i dont know? there is one thing i noticed though, the preveous owner disconnected the heater core from the system, could that be constricking the water flow?

Thanx for the info!

The AIR DAM is normally a piece of plastic or sheet metal just below the bumper. Sometimes it's built into the front grill area just behind the bumper. This AIR DAM causes the air not to flow directly under the engine compartment causing the LOW PRESSURE area. By doing this, it allows the air to flow thru the radiator, across the engine area and out under the vehicle.

The heater core being disconnected could be your problem. Some engines have a BYPASS hose on the water pump to circulate coolant thru-out the block while the thermostate is in the closed position. This keeps the engine from creating HOT SPOTS within the heads while warming up and normal operating. Some engines and most today use the heater core for this purpose. If you have no bypass hose on your water pump which is normally a short hose from the water pump to the intake manifold, then your engine is using the heater core and the hoses probably run from the pump area to the heater core to the intake manifold. Let me know what you find.

ya there is no air dam under the engine compartment and no bypass hose on the water pump either. it looks like the heater core was leaking at one time and thats maybe why it got disconnected. with the air dam under the engine can i fabricate one, and if so what would be the best way?

Thanx

Being a 1977, it may not of had one. I have a friend that has an all stock 1977 F100 Ranger. Basically the same body style, just lower. I'll look to see if it has one as he bought it from the original owner, so it has no modifications.

Looked this week-end at my friends truck. No air dam under the bumper. They probably didn't have them then as the engine thermostats were normally 180-190 degree units. With emission controls, the engines need to run about 210-220 degrees and require good air flow thru the radiator and engine compartment. I would start with connecting the two heater ports on the engine together with a lenght of hose that will allow unobstructed flow thru it. This will allow the coolant to circulate thru the engine to eliminate HOT SPOTs while the thermostat is still in the closed postition. This is the purpose of the bypass hose if equipped, or the heater core if not equipped with a bypass hose.

I would also recomend that, but would also check your radiator for flow. An easy quick way to do this is when it is up to operating temp (thermostat open) place your hand at the top of the radiator and feel if its warm. Do this all the way down to the bottom, and if at any point you notice an obvious temperature change (cooler), than you need to change the radiator.