Heater not very hot

[Fjordlander]

Hi all,

Merry Christmas!
I have a 76 K10 Scottsdale with no A/C and my heat never gets very hot. It gets warm at best.
I replaced the thermostat and that didn't make any difference. I might try and bleed the system just in case there's an air bubble but I'd appreciate any advice on other things I should check.

 

[AuroraGirl]

Hi all,

Merry Christmas!
I have a 76 K10 Scottsdale with no A/C and my heat never gets very hot. It gets warm at best.
I replaced the thermostat and that didn't make any difference. I might try and bleed the system just in case there's an air bubble but I'd appreciate any advice on other things I should check.

have you flushed the heater core? how does your coolant appear? muddy?

 

[Fjordlander]

have you flushed the heater core? how does your coolant appear? muddy?

I haven't flushed the heater core. I'll look into doing that.
Coolant is clean looking. It's bright green like it's fresh from the bottle

 

[Finkaire]

Typically there is a heater control valve that opens and closes on the engine side of the firewall. My Pontiac and El Camino have a cable. I looked at LMC parts for our truck and don’t see one, my thought it’s in the passenger compartment or it’s controlled some how else, maybe door activated? Let us know what you find.

 

[GTX63]

Flop down on the passenger floorboard on your side with your left hand on the "temp" control level in the dash. The HVAC controls are cable operated. Now, while watching the cables beneath the dash/glove compartment, slide the temp lever back and forth as you confirm the door is functioning. You are trying to eliminate the simple stuff. If you have already replaced the tstat, and you know there are no leaks/low coolant, a plugged heater core is pretty common on 40 year old Squarebodies.
The good news is that they are neither very expensive nor very hard to replace, especially on a non ac truck.

 

[HotWheelsBurban]

Typically there is a heater control valve that opens and closes on the engine side of the firewall. My Pontiac and El Camino have a cable. I looked at LMC parts for our truck and don’t see one, my thought it’s in the passenger compartment or it’s controlled some how else, maybe door activated? Let us know what you find.

I want to say that square body trucks don't have a factory heater control valve? Dad had to install a manual shutoff valve on several of our trucks, because the warm coolant going through the heater core year round, in the summer it affects the performance of the AC.

 

[fast 99]

After getting all the other items checked out and still no heat.

Get engine up to operating temp with open thermostat, heater control on hot with fan on high. Using a heat gun check the hose temperatures close to the firewall. Any temp spread exceeding 20 degrees, needs a new core. Doesn't matter much what the temperature is just that the spread is small. Reason for this is the coolant is staying in the core too long [not circulating] losing a lot of heat. A good core temp spread will be less than 5 degrees.

I have had limited success backflushing cores with a garden hose. Have to be careful, may blow out core if too much volume is pushed in. If the core is bad anyway not much to lose.

 

[sidschev]

you have the hoses routed the right way ??? just a thought. you either have one hose going to the rad or 2 have the hose going to water pump and one from intake manifold

 

[Radiohead]

Not sure Sid if reversing the hoses to the heater core would change much, all else being correct and equal. Simply feeling both heater hoses when everything is up to temp and set to make cab heat should show how much heat drop is going on. One hose should be a little cooler than the other, not a whole bunch.

Thanks for the diagrams on flow, that's great information for the uninitiated.

 

[Octane]

Sometimes a good low pressure water flush works.Other times a core is just too old and corroded.I bet I ran 75 gallons thru one once,before it cleared it enough.

 

[rich weyand]

I put a cover over the center of the grille in the winter. I just used a Chevy Truck fender pad.

You must be registered for see images attach

 

[PrairieDrifter]

A regular cab should heat you out. A blazer will most likely not and a suburban won't, depending on the temp. Maybe the seal on the blend door is junk, or it's not closing completely. My 79 will roast you out in negatives.

I wouldn't be surprised to see a clogged heater core either, they usually let some heat go by, but once you turn the fan up or even engine revving can change the temp.

 

[Shorty81]

you have the hoses routed the right way ??? just a thought. you either have one hose going to the rad or 2 have the hose going to water pump and one from intake manifold

This is good information. I once routed my hoses wrong and did not get good flow to heater core.

 

[Octane]

A core can be clogged in two ways,surface dirt and corrosion built up after many years,and/or core internal corrosion/dirt.I find the combination is of course the worst situation for not having good heat.

 

[Grit dog]

I put a cover over the center of the grille in the winter. I just used a Chevy Truck fender pad.

You must be registered for see images attach

Cool truck and pic, but to be clear to the OP, his issue does not surround not having or needing a winter front. Unless maybe it was -30 and he was driving it on the highway during his observation.