Heater Problem

[Cliff883]

Well I searched everywhere and can't find anything on this forum or online for my problem so here I go. I have a 1988 GMC Sierra with a 305 and no equipped air conditioning. For some reason the heat just blows luke warm or slightly warmer. I have flushed the core even tho it was already getting to hot to touch before that. The coolant is full, and the blend door at the core is working properly. Is there another blend door somewhere that I need to check? Or is there something else I can check? Any and all help will greatly be appreciated.

[rodram]

Hi... whenever this has happened to me... my first suspicion is always the thermostat

 

if the thermostat is broken or stuck in wide open position, then the engine will not reach a temperature required to create normal heat in the heater core and vent system in your truck... you likely need a new 195 F thermostat

[Cliff883]

I forgot to mention that the thermostat is only a year old and the truck runs at about 190 when warmed up.

[rodram]

....mmmmmhh

 

well, are you getting good circulation of warm/hot coolant through the heater hoses and core?

- is the heater core partially plugged up?

- are the hoses in good condition? separating inside/internally ?

- any chance of you getting excess air in the cooling system..? or an air-lock of some kind..?

[gscalifornia]

I'd still suspect the heater core. Once they start plugging up flushing them can't usually remove all the gunk.

[Cliff883]

Well I did have to top off the coolant level after I let it cool from when I removed the core and it is heating up better. I guess the flush did help.

[mpaquette]

I had the same issue on my '95 K1500. Turned out to be the thermostat. Make sure you check the new thermostat by putting it in boiling water to make sure it opens. I've bought more than one thermostat that didn't open in boiling water which equaled no heat in the truck.

[Cliff883]

I wasn't sure what size thermostat I had in it so I replaced it again with a 195 and decided to change the heater core as well. I still am not getting great heat. It does get ok warm after an hour but thats with the heat all the way up. The temp gauge is reading around 180 to 190 in this cold weather. Does anybody have any ideas or does it look like I am just going to have to just suck it up and deal with it?

[Cliff883]

Hello? anyone? And to add to everything else, somehow snow is coming through my heater vents. How is this possible?

[thebandnerd03]

one option is to try putting in a lower temp thermostat. I went with a 185 and now my truck is a sauna. It got so hot that i acctualy had to go back to the 195. No point in driving in the winter with your window open. And as far as snow in your vent system check the blower motor housing and the wiper cowling. that happened on my sentra and turned out that a portion of the cowling screen was missing. Hope this helped.

 

P.S. check the tempo rating on your anti freeze.

[Cliff883]

I thought the higher degree thermostat would let the coolant get hotter?

[thebandnerd03]

yeah i wasnt paying attention to what i was saying. i had it backwards. go to a 205 or 220. i cant remember what one i used but that will help out. probably should stop posting after getting off a 12 hour night shift.