Hey guys. Need a bit of help with my heater box. A few months back I completely rebuilt it, and that entailed installing a new heater core. The engine is an in-line six, with the temperature sensor for the gauge in the rear of the block. The heater didn't work for a few years. It was full of leaves in the core was plugged, and that didn't matter much since I California. But now that I rebuilt it, I want to use it on the chilly mornings. Since I rebuilt it, I can only get intermittent heat. I've gone through every test that I can think of to determine why I can't get constant heat out of the heater. I have tested the flow of coolant in and out of the core, and found it to be moving well. I have tried switching the lines. That had no effect. I have jacked up the truck in the front and let it run in that position so that it cycled through several thermostat openings and closings, hoping that in the air in the system would have flowed to the radiator since it was high ground. That did not help. However, I did notice that while it was sitting there running and I was feeling the air flowing out while all the time watching the temperature gauge, that the hot air would start coming out at the peak of the heat cycle. By that I mean that I have an electric fan with 195° thermostat. The coolant heats up until it reaches 205° and then the electric fan turns on and the temperature immediately begins to drop until it goes down to about one ninety-five, and the fan turns off the heating cycle begins again. What I noticed is that I'm getting heat when the temperature reaches the highest point that he cycle. By the time the temperature has dropped down to one ninety-five, the air is cool again. And this is happening after the engine has warmed up. The thermostat has opened and closed several times at this point, in both the block and the coolant in the radiator have reached their running temperature.

So, I'm wondering, if because I have a large aluminum radiator, if my fans Are cooling the coolant too much. Is that possible? Does some of the coolant stay in the radiator long enough to go through two cooling cycles? I would really like to get some feedback on this and get some answers, and better yet, be able to resolve this so that I can use my heater on a regular basis.

 

If the thermostat is getting her up to 190 or more and holding it there, it ain't the radiator at fault.

Was the truck ever AC / heat / vent or is it always been strictly heat / vent? Reason I asked, some delete parts of the AC and keep the box and controls, and there are doors.

 

Hey there. Truck has always been w/o AC. There is only one entrance and two exits in the heater box. The entrance is fresh air intake. The exits are heat into the cab close to floor, or under edge of dash, and the other is the defrost. I had the box completely apart. The diverters work well. Fan is moving air.

 

Are both of the heater hoses hot to touch ?

 

I'm guessing you have a real temperature gauge. What I have done before is use cardboard in front of the radiator to inhibit it's ability to cool, so that coolant in it is maintained some warmer in the radiator in that cold wind so that when the thermostat opens and cycles coolant, warmer coolant is picked up by the engine. The thermostat will still open and shut as needed, but likely stay open longer which reduces time spent stagnant in the radiator.

If you use cardboard to block some air flow, watch the gauge. If we make the radiator to inefficient, the engine will heat up and then, we need to adjust the cardboard.

Forget my prior post above, it was aimed more at the notion of a radiator being too efficient ... but in your case ... maybe the engine just isn't making hot coolant fast enough and then when it does and the T-stat opens, coolant that has been sitting long suddenly enters via the lower hose and some of that might be going into the heater core.

I know it reads like a cop out, but an over efficient radiator is a foreign notion to me. An engine stretched out length wise like a I-6 is .... might just not heat enough coolant fast enough to satisfy the need for hot coolant.
A V-8 has 8 cylinders exposed to a water jacket, and only one side of each bank has any of that water jacket next to an exterior side of the engine block ... and it has a hot manifold there too.
An I-6 has 6 cylinders exposed to the water jacket and both sides are next to an exterior surface of the engine block, where cool air does cool the block some ... and a I-6 has exhaust manifolding on only the one side, the other side being naked.

Cardboard will also reduce the amount of air on the engine block exterior surfaces. I hope I made some sense.  Heat is energy and while we can't create energy ... we can transform it.

Please don't use that cardboard poster of Farah Fawcet from the bedroom door. 

 

He has 2 pages over here https://www.ford-trucks.com/forums/1...-cool-air.html
He said the hoses get "burning hot" I just dont know if they stay that way all the time as he said when the efans come on the heater temp goes cold? If the stat was working as it should the radiator cooling should not be a big deal.
He also said the air deverter I am guessing defrost / floor, is working but he did not say anything about the temp control.

I asked if the temp control is a vacuum valve in the heater hose or some other way?
I think it is a issue with the temp control or a box issue.
Dave ----

 

Maybe this will help then????

 

There is no valve of any kind in the hoses to/from the core. Never has been and the heater used to work fine.
Can anyone tell me what item #16 in this illustration is and where it is supposed to be installed? https://www.lmctruck.com/1973-79-for...fresh-air-type

 

I don't have a just heat box any longer, but this above is my effort to explain a simple mod a friend did to his '70s tow truck for better heat on calls. Stock, the heater or vent door on the passenger side draws air from that colder outside air vent in the passenger kick panel. My friend used something, maybe a foam block wrapped in plastic stuffed in the kick panel opening to block the cold air from the cowl, and left the passenger floor vent door open, and then the heater was drawing air from the warmer passenger floor vent door opening. Recirculating heated air. I forget exactly what he used, the "foam in plastic" is just an idea I came up with, could be squeezed and pushed into place through the passenger floor vent door. A small pillow would work, just put it in a Walmart bag. One could even take the rubber sleeve loose from the kick panel and simply cover the kick panel hole, leave the rubber sleeve out and let it draw from the now open gap between the air inlet and blocked off kick panel hole.

 

Ok no valve in the heater hose.
Then what controls the temp to the truck?
It is 1 thing when it is 20*f out you want full heat but say it is 50*f and you need just a little heat to take the chill out?
You move the temp lever what dose it do to adjust the temp?

#16 looks to be a valve that bolts to the intake manifold on v8 motors after VIN xxxx
It looks like before that VIN they used #17 Elbow.
So there has to be something to control the temp at the heater box like a blend door to close off outside air if you want full heat or open it a little if you want only a little heat.
Dave ----

 

There is either heat on or heat off. You can control how fast the fan is blowing the hot air, or turn the fan off, but there is no other heat control method.
I am leaning toward the problem being with the efans. As the engine temp reaches 205*, the heater begins blowing hot air. Once the fans turn on, within maybe 20 seconds the temp of the air being blown begins to cool. I will place a piece of cardboard over half the radiator and see what affect that has.

 

There has to be a way to control the temperature other than on & off of the fan????

Post up a picture of the heater control as something is not right.

If you think its the efans check the heater hoses both when you have heat and when you dont.
I bet they are hot both times when checked.
Dave. ----

 

That is an in line vacuum operated heater valve, goes in a heater hose between engine and firewall Original was metal, replacements are plastic. Normally open, vacuum pulls it shut. .More Information for FOUR SEASONS 74612 (rockauto.com) At < half. the price. When my truck was just heat, I don't recall there being one on mine .... but I know it has one with heat/AC I installed. Seams to me that there were two cable operated doors in the heater box, one decided hot vs cooler like a diverter door pre heater core .. and the other controlled user's choice of floor heat or windshield outlets. My original heater controls did not even have a vacuum switch to operate a vacuum heater valve as far as I know.

Time to lay on your back in the floor and verify that a door operates with each move of either top or bottom control panel lever. I think maybe was the upper lever marked temp ... or cold vs hot .... and the lower lever marked maybe off --- heat --- defrost. It's been 35 years since I studied one in person.

 

I have confirmed that. The diverters work well. Thanks.

 

Both of them?
You said in a post you did not have a temp control but now you have 2 control levers?
Post pictures
Dave ----