I don't get any heat from the heater in my truck. I've searched and applied everything I found. Nothing.

Here's the setup- 460, 4 core radiator, 195* thermostat, standard heater.

Here's what I know- Water pump is used but is pumping water just fine. The heater core is flowing coolant, no obstructions. Truck runs a solid 190*.

I've gone many rounds with my heater and still can't find the problem. I thought maybe the heater core was airlocked so I added a T in the heater hose to bleed the air. No luck.
Checked the heater core for flow restriction. Flow is fine.
I pulled the heater box out and checked for debris and proper operation. The heater core is clear and all the ducting and valves are working properly.
Reversed heater hoses on heater core. Still no heat.

At this point I'm stumped. Anyone have any other ideas?

 

So the fan blows air, but the air isn't getting hot? Does it get warm? Or same temp as outside?

Do the heater hoses get hot? Check that the warm/cold door operates correctly. Might unhook cable to make sure that's not holding it back.

Is it an a/c truck, or non a/c?

Marty

 

Ooops, I was in a hurry when I posted this and left out a few details.

It is a non-A/C truck. Yup, the fan is blowing air. The air is always outside temp no matter if "Heat" or "Defrost" is selected.

The heater hoses do get hot but I'm still not 100% sure both are getting hot from coolant flow. One of the hoses COULD be getting warmed by the headers. It's a little tough to tell. However, when I pull the heater hoses I get coolant flow from both sides of the core.

Before I took the heater box out I pulled the cables off and checked for freedom of movement. Everything checks out OK. When I took the box apart I double checked the air valve operation and everything is the way it's supposed to be as near as I can tell.

One last tidbit which could've been my wishful imagination..... When I reversed the hoses (after I added the T) it seemed like I got a little heat for a minute. When I reversed the hoses the T I added got moved to the hose that is lower on the firewall. I am wondering if this made it so air got trapped in the upper hose again??? That's my last idea.

 

so is your 4 core an aftermarket replacement?
if this is bigger than your stock one your steady 190* running engine may be to low for the 195* thermostat to fully open. you could just be too eficient in the cooling department. when I put in my 4 core I dropped almost 10* and lost "some" heat and increased the time for the engine to warm up to get heat, but not as bad as you it would seem.

I would try to get the temperature up. maybe tape a peice of cardboard on the front of the radiator (12" sq or so) and then watch how much the coolant flows with the rad cap already off.

 

This might sound dumb, but do you have the heater hose connected to the right port on the water pump? I think this can affect the amount of coolant flow through the heater core. And as far as I can tell, it shouldn't matter which direction the coolant flows through the heater core.

 

ranchero77, yup the 4 core is a replacement for the 2 core I pulled out. I started out with a 180* stat. When the 180 was in there I blocked off the lower half of the radiator and only saw a 5 degree rise in temp. I then tried blocking almost the entire radiatior (had about 20 square inched showing) and the temp shot up to 220+. Still no heat. However, that was before I tried everthing else. I'll go try the cardboard again to try and get around 210 degrees.

loudfords, that doesn't sound dumb at all. I had to double check, but there is only one port on the water pump for a heater hose. The other is on the intake. Not being farmiliar with the coolant flow path through the WP I reversed the hoses thinking maybe the water pump was pumping cooled water straight from the radiatior into the heater core. I didn't figure it made a difference either but I'm clutching at straws here!!

 

It sounds like your "water-side" of this is working right. I would go back and make sure the air-flow is right. It sounds like outside air is blowing around the core and not thru it.

 

There was an earlier thread on the problem with the outside air flaps always being open but I think that was on an a/c truck. The idea was to have fresh air in the cab at all times as opposed to recycled. You've said you checked the flaps though right?

 

I think I would still take the heater hoses off of the core and backflush the core with you garden hose and make sure water is flowing through the core. Do it easy so you don't rupture your heater core.

 

If the thermostat is working properly and it is running 190* like you said, then the bigger radiator has nothing to do with it not heating. No water gets to the radiator until the thermostat opens, so we can rule that out.
I would replace the heater core, it could be flowing water, but is the whole thing flowing or just a small part the is just enough to move some water?
If you are going to pull the heater box again, anyway, Go ahead and replace it, they don't cost a whole lot.
Jimmy

 

Well, I tried blocking off the radiator again. With about half of it covered with an abient air temp of around 40* I managed to get it to run at 205*. Still no heat. None. Not even luke warm.

460f250, yup I've checked both flaps for freedom of movement and proper air diversion. With the cables connected and the box assembled, everthing works OK. When "defrost" is selected, it pulls in fresh air from the cowl and blows it out the defroster. When "heat" is selected it pulls air in from the cab and blows it out on the floor. If I disconnect the cables, the flaps move with ease. As near as I can tell, the box itself is working the way it's supposed to.

bushman, before I added the T in the heater hose I ran a garden hose both ways through the heater core. It seemed to flow very easily each way. I got a full stream of water coming out when holding the hose about 2" away from the opposite heater core fitting. But I'm not ruling it out yet.

lxman1, so far I think a partially resticted core is the most likely possibilty. I am a little skeptical considering the excellent flow it seems to have while flushing. Perhaps the water pump is a little weak and a partially restricted core is keeping it from pumping water. My 4 row radiator may be covering up for a weak water pump.

I'm going to get a new heater core Monday to see if that helps. If that doesn't work I'll get a new water pump, which I could probably use anyway. What do you all think???

I really appreciate the ideas!! I've been going nutz racking my brain on this. It defies logic.

 

I'd say the core sounds fine. I would suspect the door that controls the warm/cold.

Marty

 

Well, I had to blow my water pump/heater core fund on some new lockouts today. I had a wheel bearing nut split and release tension allowing the hub/rotor to walk into the lockout and grind it to bits. Hopefully I can find a spindle tomorrow and get it back together so I can concentrate on the heater again.....

 

Check your vacume lines on the heater and blower dash controls. I bet you have something reversed?

 

I'm going to change my answer....it sounds like you are not getting water to flow from the motor thru the core back to the motor. Causes for this could be the hoses plugged or maybe the fittings. If the motor is cooling OK then I would think it would there.