Heater blows cold

[svlsmokey]

***Not finding this but I'm sure its been covered before. Maybe someone can point me in the right direction.***

I loaned the M1028 to a friend and they moved the lever from Hot to Cold and now the heater only blows cold air. I checked the linkage from the lever to the heater and that much is working. The lower hose into the heater is pretty warm but the top one is cool. The engine was plenty warm and the coolant level was full. Outside air temperature was 30 - 35 degrees. I haven't had time to look into it further - maybe tomorrow when the weather warms up a little more.

Thanks for any ideas...

 

[Tinstar]

There’s another thread on this page that covered this somewhat.

Bent linkage would explain blowing cold air, but not cold hose.
Sounds like a possible clogged heater core.

Maybe just coincidence with your friends using it.
Did they go four wheeling? Maybe knocking something loose inside the cooling system?

 

[Tinstar]

https://www.steelsoldiers.com/showthread.php?173176-Heat-works-but-gets-only-slightly-warm

My mistake
Second Page.

 

[svlsmokey]

Probably coincidence. No - he was just hauling stuff to the dump. But you know how it is - other folks don't know the quirks of the truck.

I'll start by checking the heater door position, then I'll clean the core. I'm also thinking thermostat. It gave pretty good heat a month or so ago so that might have gone south.

 

[Tinstar]

Replace thermostat with the correct one.
The 6.2L takes the “hockey puck” style.
Other standard style will work, but is wrong for this engine.

This is the correct one.
https://www.rockauto.com/en/catalog...diesel,1053021,cooling+system,thermostat,2200

 

[svlsmokey]

I topped off the radiator and let it burp a while and its blowing hot air again - at least while idling in the driveway. Maybe that "Coolant Low" light really means its low...

Top radiator hose never got hot. Might need a thermostat yet? Or maybe need to test it out on the highway first...

 

[cucvrus]

A typical Chevy/GM the first thing that starves for coolant is the heater core. Now you should figure out where the coolant is going. But that is pretty normal to have cool heater and low heat when the coolant is low. Feeds from the top right side of the radiator. Good Luck.