Heater queation 2000 Blazer

Guys I know this topic has been beat to death here, but I seem to be having a little diff. problem that I could use some help on. When the outside temp is 70+ my heater will blow very hot air and both hoses on the core are Hot. This morning temp was high 50's and when I turned on the heat for a quick temp adjustment, it blew cool air and the outlet hose on the core was only slightly warm. Checked the damper system for function- you can hear the motor moving the door and the temp will going from cold to warmer(why can't it be hot!). This problem started last spring but I put off fixing it when it warmed up and the heater seemed to start functioning normal again. Why the sudden no hot water going thru the core with only a slight cooling of temps. checked it a couple days ago when it was 75+ and both hoses were very hot to the touch. Any help???

Guys I know this topic has been beat to death here, but I seem to be having a little diff. problem that I could use some help on. When the outside temp is 70+ my heater will blow very hot air and both hoses on the core are Hot. This morning temp was high 50's and when I turned on the heat for a quick temp adjustment, it blew cool air and the outlet hose on the core was only slightly warm. Checked the damper system for function- you can hear the motor moving the door and the temp will going from cold to warmer(why can't it be hot!). This problem started last spring but I put off fixing it when it warmed up and the heater seemed to start functioning normal again. Why the sudden no hot water going thru the core with only a slight cooling of temps. checked it a couple days ago when it was 75+ and both hoses were very hot to the touch. Any help???
Start by flushing the system specifically the core. Sounds like a partially plugged core to me. Don't forget the new rad cap. Any chance the T-Stat is stuck open?

Start by flushing the system specifically the core. Sounds like a partially plugged core to me. Don't forget the new rad cap. Any chance the T-Stat is stuck open?

Rick,
Backflushed the core with garden hose and fitting. Flow is strong and didn't notice anything coming out but clean antifreeze and clean water. temp is 71 out right now and the heater is hot. Antifreeze was changed out last winter (46,000 miles) and is still clean and clear. Stat seems to be working ok, temp reads 195 or so when it's warmed up. The changing when the outside temp drops around the 50's still puzzles me. anymore ideas? Forgot to add- cap is new from antifreeze change (not Delco cap).

Rick,
Backflushed the core with garden hose and fitting. Flow is strong and didn't notice anything coming out but clean antifreeze and clean water. temp is 71 out right now and the heater is hot. Antifreeze was changed out last winter (46,000 miles) and is still clean and clear. Stat seems to be working ok, temp reads 195 or so when it's warmed up. The changing when the outside temp drops around the 50's still puzzles me. anymore ideas? Forgot to add- cap is new from antifreeze change (not Delco cap).

If you've flushed the core and it isn't plugged, I'd watch the temp gage as the weather starts to cool to see if you reach operating temp. I have to lean towards a stuck or sluggish T-Stat.

I'm strickly speaking from a cooling system perspective, if there is a vent door not opening/closing somewhere, all bets are off.

Will try the stat change this weekend if possible. It's worth a shot considering the small price of one. The doors seem to be operating properly. You can see the shaft turning the gate with the glove-compartment removed when you turn the knob, and the temperature changes with the gate opening.

Will try the stat change this weekend if possible. It's worth a shot considering the small price of one. The doors seem to be operating properly. You can see the shaft turning the gate with the glove-compartment removed when you turn the knob, and the temperature changes with the gate opening.
I agree, it is the lesser of all evils. I have seen T-Stats get slugish as well as stick wide open even after they're removed. I have also seen heater cores get partially plugged too. You can get water/coolant to flow through them, but not enough to keep them hot.

Try a new T-Stat, and If that don't work, I'd think about a revesre power flush on the core.

Will try the stat change this weekend if possible. It's worth a shot considering the small price of one. The doors seem to be operating properly. You can see the shaft turning the gate with the glove-compartment removed when you turn the knob, and the temperature changes with the gate opening.

How did you make out? Did you replace the T-Stat?

How did you make out? Did you replace the T-Stat?
Hello Rick,
Replaced the T-Stat with another 195 and the heat still seems to be very hot coming from the vents- the temp outside it still hanging in the upper 60's to low 70's so I'm waiting for that drop to see if the backflush and the T-Stat change worked. Did take the old stat and drop it in some boiling water to check it out, seemed to open all the way and pretty quickly. Will see what happens when the temp drops. Thanks for the help!

Hello Rick,
Replaced the T-Stat with another 195 and the heat still seems to be very hot coming from the vents- the temp outside it still hanging in the upper 60's to low 70's so I'm waiting for that drop to see if the backflush and the T-Stat change worked. Did take the old stat and drop it in some boiling water to check it out, seemed to open all the way and pretty quickly. Will see what happens when the temp drops. Thanks for the help!

Good Job! I'll keep my fingers crossed for ya.