heater issues

[fender89]

so now that its -15 out i guess i need heat. only blowing lukewarm out of vents. i checked coolant levels are good. top of the radiator. both hoses running to the core are hot. i took them off today and flushed out both ways. still not blowing anything but lukewarm. from my understanding its a super simple design, hot coolant flows thru a radiatior, fan blows over it and creates heat. if when i flush it comes out both ways just fine where is the problem?

 

[Octane]

If it has an underhood heater control it coukd be stuck.But my 77 K10 doesnt have one.I'm gonna flush heater core soon.If good airflows coming from floor vent, core may still need replaced, if outside surface of core is caked with dirt and crud.Regardless of hose temps.

 

[Radiohead]

Is there a discernable temperature difference between the two heater hoses when hot and set to max? If it's a lot, maybe then the core is plugged or the valve is the restriction. Try cardboard in front of radiator.

 

[85K304SPD]

Maybe the thermostat is stuck open.

 

[fender89]

there is no hot water valve on the hose. i checked the the thermostat and its working. main rad hose was cold and hot . i guess i gotta replace the core..

 

[gmbellew]

could also be a blend door issue if the outside of the heater core isn't covered and preventing air flow? not sure about the earlier systems, though. I have a 1990. but something to look into. you can get a better view of some of it by removing the glovebox. depending on your system. their may also be a part of the ductwork under the glovebox that ks easily removed to check out the ble d door action

 

[fender89]

i took apart everything under dash to get visual access to the blend door function. it seems to be sitting all the way in the hot position....i think

 

[fender89]

i wonder if the fins are full of **** on the outside

 

[Rickf]

I'd check for nesting materials.

 

[Snoots]

i took apart everything under dash to get visual access to the blend door function. it seems to be sitting all the way in the hot position....i think

Don't think, know.
I'd bet on trash in the plenum.

 

[87gmcburb]

so now that its -15 out i guess i need heat. only blowing lukewarm out of vents. i checked coolant levels are good. top of the radiator. both hoses running to the core are hot. i took them off today and flushed out both ways. still not blowing anything but lukewarm. from my understanding its a super simple design, hot coolant flows thru a radiatior, fan blows over it and creates heat. if when i flush it comes out both ways just fine where is the problem?

I had same issues in the past. I would strongly suggest looking at the blend door clip. OEM is cheap plastic and all 5 of my SB had broken ones. Here is a pic of one from the part guy.com. They sell an aluminum one. If you go this far get a rebuild kit and replace the seals, vacuum lines and vacuum check all of your actuators.

 

[fender89]

i have removed the heater box to get a closer look. the blend door is functioning fine no debris in there and the heater core is newish. guy i bought the truck from replaced it in 2017 it looks.. now im at a loss. wtf

 

[scrap--metal]

Is the vacuum line to the firewall still in place?

I think that's necessary to get everything functioning properly, and I don't see it mentioned above.

 

[SquareRoot]

Vintage Air

 

[fender89]

At this point I'm thinking thermostat stuck. Just got one in town putting on later today