Hi i have a 73 f100 360 it loos like it had at one time a/c the dash is set up for it and it has the big airbox. when you let it warm up and sit in place for a while the heater blows warm but not hot but when you take off driving it starts to blow luke warm it has a thermostat but could it be stuck open i don't have the temp guage working yet but the heater hoses and radiator hoses get hot like they should any ideas thank you

 

It sounds mostly like a heater core problem. If you get the guages working that could give you an idea of the engine temp if it is changing once you get moving. A bad heater core can cause it to blow hot, then cold, then somewhere in between.

 

Get the engine to operating temp then touch the heater hoses for how hot they are.
If one is really hot with the other being less hot,the problem is heater core.

What does the temp gauge read?

If it works properly & hangs around the N in Normal ,then it probably has a 165*F thermostat in it (That's bad, btw)
The engine requires a 195* F thermostat year round , in hotter climates a 180* can be used but no cooler.

Do that test and get back to us.

 

I Agree I Just Replaced They Heater Core In My 78 It Woul Blow Warm To Hot Air When Idling But Soon As You Drove It Or Left The Fan On High For Very Long It Was Cold I Put In A New Heater Core And Now It Will Run You Out Of The Cab Picke My Heater Core Up For Less Than 20 Bucks New They Are Not That Hard To Put In

 

Thank you both lines of heater hose hot i was thinking mabey a stuck open thermostat? or to cold I grounded my temp guage a couple of weeks ago and it went just to above the c-cold mark should it go all the way to thw h-hot side

 

Maybe the box is full leaves ?

 

Not to hi jack this thread,
But how do you replace you're heater core? I know mine is bypassed because thats how it came to me from my uncle, but Ive read manuals and all, and all of them say to take it to a repair shop. I hate to do that seeing as how they always raise prices.
Thanks,
-Chris

 

You're reading the wrong manuals. Get the manual on cd from this site. It has the step by step on heater core replacement as well as a lot of other usefull info.

Meanwhile check this out (if you have factory AC -- which is what those cheap manuals usually recommend taking to the shop).

https://www.ford-trucks.com/article/...es_Trucks.html

 

73F350SC,
I have a 1979 F150 4X4, that I will be replacing the heater core on in the next day or two. These trucks have what appears to be 4 seperate types of heating systems; air,non-air, air heavy-duty, and non-air heavy-duty. Mine is non-air. The manual shows six nuts that you remove from the engine side of the firewall, approx. six screws around the vent, and the heater control cable, once these are removed the entire heat box looks like it comes out. The heater core in inside the heat box. Actually, the air conditioned models appear easier, it looks like these can be replaced through the engine compartment.

I will write back and let you know how long it takes.
John24255

 

bh2112,
As was previously stated, the best 1st step would be to get the engine up to operating temp. You will know it is up to operating temp when the upper radiator hose gets hot, if this hose doesn't get hot, you may have a thermostate that has stuck open. In this case, the heater hoses will be luke-warm as well.

If one heater hose is hot and not the other, water is not flowing to or through your heater core. A plugged heater core and cause this. Also, I have seen some heating systems that have a valve which shuts off the water to the heater core. These are mostly used on air-conditioned models. If so equiped, this valve could be truned off or malfunctioning.

If both heater hoses are hot, this means water is moving through the system, and the heater core may be OK. The fan blows air across the hot heater core to heat the cab. If a vent is stuck open, this could cause cold air mix with the hot and rob you of the heat.

Looking at the diagrams in the service manual, it appears as though the heater core is easier to access in the A/C models. I believe it is located in the engine compartment near the firewall on the passenger's side. If you remove the covers and the hoses hook straight to the heater core, and the hoses are hot anf the heater is not, it is probably time for a replacement. I believe they are about $17.00 at Autozone.

Please write back and let us know what you find.
Thanks,
John24255

 

Well I know for sure that mine has air from the factory. What is the difference between air and air heavy duty?
-Chris

 

I think he is thinking *High Output Heater*.

 

isnt a high output heater 2.5" thick and a standard one is 2"?

 

on the passinger side floor there is a vent that opens to the cab i can see the heater core through it.Looks like there is a vent just to the left of the heater core looking through that vent i think it is not closing all the way or it is being blown open. is there a book that is good at covering heating systems?

 

In the middle of changing the heater core on my 79 F250, and here's what I've learned, if it's helpful:

Trucks of this era come with 4 different sizes of core: 6x 6", 6x7", 6x8", 6x10". I happen to have the 6x6".

I do not have A/C, so the heater box is very simple. Three bolts total in the engine compartment, two where the hoses meet the firewall, one towards the centre of the wall. Then a couple of bolts in the cab on the heater box near the vent (bottom-passenger side near wall).

It's mechanically not complicated, but it was real pig to wiggle the box out from under the dash - a very tight fit.

One major design flaw I see is that the box is liquid-tight. So your heater core can be leaking for a long long time and fill up with antifreeze sludge before any drips occur to alert you. I should have recognized the sweet smell (but I'm nasally challenged apparently) and the excessive humidity on the windshield (antifreeze vapour).

A new core was $65 Cdn.