Riddle me this........ truck heat.

[Mike D]

Riddle me this........ truck heat.

Didn’t some of those trucks have valves inline to regulate the water flow to the heater core?

I don’t think either of the issues you are chasing are related to not getting heat in the vehicle. Unless you have a really short drive to work and the truck isn’t getting up to operating temp, regardless of a stuck open thermostat or defective fan clutch, the coolant will heat up to operating temperature and certainly enough get some heat in the cab.


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[Texas Grown]

Your on the right track Randy. My '89 dose/did the same thing. I've replaced the fan clutch, radiator, heater core, hoses, and multiple thermostats(190-195 temp). It just runs cooler in the cooler months. But heats the cab great. I also removed the condenser from in front of the radiator for better air flow cause the old one was in bad shape enough to cause over heating issues in the summer. Mine's got 276K on a never been rebuilt 350ci with a 5sp tranny. As to the fluid loss, mine dose the very same. It's just the way it is.

[Texas Grown]

One other thing, if you're driving that truck over 65mph, you need to slow down . Mine don't like anything over 65. And dose well at 60. Gotta remember what the speed limit was when these trucks were built. It cools and heats better at those speeds too. What I'm beginning to think is the air flow under the hood is not designed the best, even with the proper fan setup. I also get corrosion in the distributor when exposed to extreme rains from moisture being thrown up into the engine compartment from the road. I've had that happen a few times now.

The fish are biting, and there's hogs to be kilt. Gotta go!

[Goldeneagle]

Didn’t some of those trucks have valves inline to regulate the water flow to the heater core?

I don’t think either of the issues you are chasing are related to not getting heat in the vehicle. Unless you have a really short drive to work and the truck isn’t getting up to operating temp, regardless of a stuck open thermostat or defective fan clutch, the coolant will heat up to operating temperature and certainly enough get some heat in the cab.


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It's got plenty of time to warm up. Some vehicles had the valve on the heater hose. This one does not.

Your on the right track Randy. My '89 dose/did the same thing. I've replaced the fan clutch, radiator, heater core, hoses, and multiple thermostats(190-195 temp). It just runs cooler in the cooler months. But heats the cab great. I also removed the condenser from in front of the radiator for better air flow cause the old one was in bad shape enough to cause over heating issues in the summer. Mine's got 276K on a never been rebuilt 350ci with a 5sp tranny. As to the fluid loss, mine dose the very same. It's just the way it is.

Oh I know they run cooler in the winter, but I'm not getting the heat in the cab. As far as the coolant loss, a guy here at the shop had an early 90's Chevy that did the same thing. He never figured it out.

[double bogey]

Low radiator water level = no cab heat. But this usually means high engine temp. Bet the heater core is clogged up. 150° water should put some heat to cab if its getting through heater core.

[texaspacker]

Did you check your fuses? Both of the fuse blocks? The one inside the cab & the one under the hood.
Your heater core is blocked/stopped up?
Your relay that controls the heater door is bad?
The heater control module is bad?
The door that makes AC or heat is funky? It's got a name but I forgot what it's called?
It could be that new radiator cap is no bueno for poop?
When in doubt whoop the Chilton book out.

[CabezaBlanca]

This one circulates through the radiator and intake manifold. Not the water pump.

If you're positive it's not the blend door I would disconnect the heater core hoses and stick a water hose to one side and check for flow. It should flow very freely.

Check or replace the thermostat.

If the water pump has the tapped bung for a fitting you could move the hose from the radiator to the pump. That will give you the most flow through the core.

I also wouldn't put a whole lot of trust in that temperature gauge on that truck.

That's all I got.

[Texas Grown]

I had heater core issues for a while. Flushed and reflushed. Turns out my block had a whole lot of corrosion in it. And kept clogging the heater core. Finally took the heater core out and back flushed the block a few times. Then back flushed the heater core. It helped for a little while. Then slowed heat down again. So I finally replaced the core again. But not before forward flushing again. That finally took care of the problem. The truck heats pretty good till I get it around 65. Then starts to loose cab heat.
That tube coming off the manifold in the back to the heater core needs to be larger. And I wish it came from the thermostat housing instead of the manifold.

The fish are biting, and there's hogs to be kilt. Gotta go!

[Goldeneagle]

Did you check your fuses? Both of the fuse blocks? The one inside the cab & the one under the hood.
Your heater core is blocked/stopped up?
Your relay that controls the heater door is bad?
The heater control module is bad?
The door that makes AC or heat is funky? It's got a name but I forgot what it's called?
It could be that new radiator cap is no bueno for poop?
When in doubt whoop the Chilton book out.

This is a 1993 model. It don't have half that stuff you just listed.

I had heater core issues for a while. Flushed and reflushed. Turns out my block had a whole lot of corrosion in it. And kept clogging the heater core. Finally took the heater core out and back flushed the block a few times. Then back flushed the heater core. It helped for a little while. Then slowed heat down again. So I finally replaced the core again. But not before forward flushing again. That finally took care of the problem. The truck heats pretty good till I get it around 65. Then starts to loose cab heat.
That tube coming off the manifold in the back to the heater core needs to be larger. And I wish it came from the thermostat housing instead of the manifold.

The fish are biting, and there's hogs to be kilt. Gotta go!

I'm checkin that tube on the manifold first thing when I get home. Read on-line that it is notorious for rusting shut. And yes, it's not the best way in the world to run a heater hose.

[Pushbutton2]

Thermostat in backwards?

[Goldeneagle]

Thermostat in backwards?

No.

[Goldeneagle]

That fitting on the intake is also known for leaking. If it has a small leak, it will leak onto the manifold and not get to the ground.

[LWolken]

also possible the heater core valve is stuck closed or the control cable to it is not working

This^^^^Probably a loose/leaking vacuum line that controls the valve

[LWolken]

also possible the heater core valve is stuck closed or the control cable to it is not working

This^^^^Probably a loose/leaking vacuum line that controls the valve. Are you sure it doesn't have a control valve?

[banzai]

Put your hands on the input and out coolant hoses that go into the firewall to supply the heater core. If one of them is blazing hot and the other much less hot, you have a clogged heater core. If one or both is very hot blend door problem.

If both lines are relatively cool, then your thermostat is probably stuck open. If this is the case, the radiator hoses will feel kinda cool also. Remove the thermostat and check it in a pot of boiling water on the stove.