I have a 93 Bronco 351. The heater has been out for some time. I found some leaks in the hoses and replaced them all. The heater hoses leading to the core are hot when engine is run. when I turn on the heater though, it blows hot (really just warm air) for only a short period. The engine temperature gauge then will jump down significantly and the heater will blow only slightly warm air. The gauge continues to fluctuate in this manner, up slowly to a certain point and then jumps back down. I dont know if the two are related or not. Does anyone have any ideas.

 

You have an air pocket in the system. When the air pocket circulates through the heater core, the air isn't nearly as hot as the coolant and so you lose heat. Air isn't good for the system either since it expands and contracts at a different rate than the coolant. Best to drain, flush, and refill the system. Check for any possible leaks too. The gauge is most likely responding to the same air pocket. The gauge should do this once a short while after starting the truck when the thermostat opens and introduces the cold coolant from the radiator into the rest of the system. After that the gauge should remain fairly constant in its reading if everything is working properly.

I just noticed this is your first post. Welcome to FTE and the Big Bronco Forum. Always glad to see another fellow enthusiast join the ranks.

 

I google so many questions that inevitably end up on a thread on this site, so I thought I would go ahead and join. Thanks for the quick reply. Ill try this out.

 

The air pocket is usually in the heater core, as it is the highest point in the system.The way I get by this is to pull both hoses off at the motor and fill the heater core.I know this can get abit messy,but be careful and quick.Once it is all back together,run the motor to full operating temp,give a couple of quick revs and the heat should come pouring out.

 

460s,

You should be able to just disconnect the return hose from the heater core (the one that DOESN'T run directly to the water pump). Then raise the end of the hose above the cowl line. This makes the end of the hose the highest point and the air will bubble up. Its a good idea to have a bucket or some container to catch any coolant that make get caught while the air is still coming out. Once the air stops and coolant comes up the hose, you can pinch the hose off, shut off the engine and reconnect it.

 

I like to do this with the engine off.No spinning fans. I can usually get my fingers in the way of these things.Engine off is safer for me.

 

Understood. Probably a good idea in the long run anyway. Last time I had to do it, I extended the hose so I could stand back from the engine bay a foot or two. Helped keep me from getting coolant all over the engine bay too.