So I haven't used my heater in quite a while. However, the last time I used it it did put out nice hot air. Now, since an engine change, and then later a water pump change, I'm getting nothing but cool air.

I thought I might have a blockage in the heater core or possibly the intake manifold which has a coolant passage, but yesterday I took off the lines and was able to easily blow through them. The odd thing is that when the engine is warm and I feel the heater hoses, one of them is clearly hot, and the return line iirc, seems as though it is hot merely from being in the engine bay. I wonder if someone can tell me whether it matters which hose goes where. I'll check in my repair manual, and hopefully that'll tell me. But as I was looking at it I thought that the return line should be attached at the top fitting which seems to be past the thermostat. Is that correct?

I'm sure that somebody is going to jump in and tell me that the cable's that control the heater in the cab have come off their control arm. However, that is not the case. With the engine running and the heater blowing, I got into the cab and checked both cables, and was manually able to flip the arms from one position to the other. But no matter where the arm was, I could not get hot air. The engine was fully warm. The thermostat is 192°, and my gauge was showing that temperature. The fluid had cycled from engine to radiator several times. Radiator was fully hot.

I would like to get this problem resolved and was hoping that somebody could tell me where to go from here. I'm a bit stumped. As I'm trying to reason out the issue, the only two possible reasons I can imagine for not getting hot air is either there is a blockage in the actual pipe or fitting which goes into the water pump and that blockage iis preventing the hot fluid from returning from the heater core via the intake manifold. But if that is the case, why is one of the hoses getting hot fluid? If fluid can't get out, new fluid wouldn't be able to get into the hoses. I also wonder whether I got the correct year water pump. I'm certain I ordered the pump for the correct year, but knowing how screwed up the parts houses are these days, I wonder whether this may be a water pump for an EFI engine. Those water pumps spin in the reverse direction. But if that were the case, the engine would not be getting ample fluid.

As always, any help is greatly appreciated. Thank you.

 

You may need to "Burp" the heater core. Raise front of truck up high as you can, pull hose off wp, cap wp. fitting, hold return hose up till just below radiator neck level, fill radiator until it comes out of heater core return line, then reconnect hose to wp. If that don't work I got nothing.

 

Thanks for the help, but I pulled the hoses and filled the core that way before I reattached the hoses.

 

I don't think restriction would be a problem, I've used those P71 hose restrictors for years and the hole is only 1/4" and still have plenty of heat. Only take a few fins open to be able blow through. Did you have engine overheat condition in the past? From Ford reverse rotation pumps had different bolt pattern, but if it's been through rebuilder who knows? I had a 68 that I swapped hoses at the core and it seemed to backflush itself. Good luck.

 

Well, yesterday I checked for a blockage or air lock in the system. Afterwards, I drove it a few miles and let the thermostat open and the coolant cycle a few times. Once the temp held steady, I was still blowing cool air. This morning I was driving around and didn't know that I had left the heating vents open but the fan off. Out of nowhere I realized that my ankles were getting hot. There was hot air coming out of the heating duct. I turned on the fan and there it was, hot air! I must have resolved the air lock yesterday, and then didn't allow the coolant to completely warm up before I tested the heater.

 

I need to try this, because my truck has pretty mediocre heat, and I know that I have a 192º T'stat in there.

 

Parts???????? I can't find seals and gaskets for the heater system anywhere! Does anyone know where to get them?????????????????????????????????????????

 

Yours is most likely like mine; it's making the heat, but the seals and gaskets in the unit are shot and allowing the system to suck cool air in and mix it with the hot air it puts out, thereby blowing somewhat warmer than luke warm air.

 

That was my initial suspicion. Pretty sure I tried loosening the cable and selecting "hot" via the lever on the heater case.

 

I thought I had this sorted out. I was getting nice heated air, nearly hot, blown out of the heater. And then suddenly last night, without changing any heater settings, it started flowing room temp air. It looks as though I'm going to have to pull the entire heater.

I seem to remember that the last time I removed the heater core that the foam seal on either end of the core were in poor shape. Does anyone know how to make a replacement? They don't seem to be available at any of the parts houses, or LMC, or NPD, etc.
Thanks.

 

The wife's 76 Mustangs heater core foam around core went bad. I went to Home depot and found some thick dense foam weather stripping. I got the core to fit nice and tight. Not sure what the temp range was on the foam but it worked.

 

https://cgfordparts.com/ufolder/sele....php?c=3&s=142

https://cgfordparts.com/ufolder/sele...=3&s=142&g=986

https://cgfordparts.com/ufolder/sele...=3&s=142&g=985

 

Thanks for the links. However, all of those products show Ford up to 1972. Are they the same heaters and seals for a dent?

 

Thanks! That's pretty much what I suspected. Cheers.

 

Sorry I did not dig that deep on the site, I just barely remembered the name. Did you dig on the site for 73-79 stuff? I do not know 67-72 stuff, but that forum group might know the answer.