yes. this is the same valve. In looking at it -it's not the valve. I'm just at a loss. I suspect both heater cores could be clogged up. Perhaps this history is relevant now. Earlier in the year, a buddy and I replace EVERYTHING - Water pump, most hoses, the valve, radiator, thermostat, the plastic "y" and "t" pipes etc - all engine compartment components i could get to, etc. Heat worked good then, BUT - My buddy (who has worked on cars longer than I have) strongly suggested I add radiator stop leak as the last thing so as to ensure any leaks would be sealed. I have always suspected this stuff but I figured he might know something i didn't.

Shortly there after the front heater quit working. The back still didn't work.

I learned something about the vaccum and water flow options on the valve. The default is to allow the heat to work (And flow), it takes VACUUM pressure to cut it off and allow the A/C to work properly.

 

I'm at a loss now, unless its the heater cores. I'd do the rear one, but not the front one. I could be dealing with a heater core up front and still haven't ruled out the temp door actuator motor in the back. Anyone got a diagram of how the rear is put together or know where i can view a real GM Shop manual online for a few short minutes.

 

One more thing I will mention that is troubling me... unlike before - the temp guage seems to fluxuate alot now. Used to run rock solid at about 185 degrees. NOW I see it rising to 210 (and in recent days higher when idling) and then it drops back down. It will run in the 140's when driving and then back up to 185 when idling. NEver used to vary this much at all. Guess i should also point out that i replaced the fan clutch in the spring we all. all NAPA parts.

 

Pull both heater hoses at the water pump and block and squirt a garden hose thru one and see if water comes out the other. If not then probably need to flush the system.

The only "stop leak" I use is Bar's and have never had a problem w/ it clogging. Always stopped the leak.

 

Change the thermostat again or put the old one back in.
Sounds like it is not working (sticking).

It is not unusual for a brand new one to do that.

I prefer to use the Fail-Safe brand.

While you are checking to see if the heater cores are flowing water with the garden hose, reverse the flow several times to flush them out.
But when using the garden hose, just hold the water hose to the heater hose by hand. It will be messy bit you do not want to of pressurize the system.

 

I will flush the system this weekend. Thanks for the feedback. in the meantime, a battery powered heater is going to have to do...

 

Did you get this fixed? What was the problem?

 

Replace your thermostat.

 

Know this is an older thread, but my 98 k2500 had the same issue. It was intermitten heat and now no heat. In addition the temp gauge fluctuates quite a bit. Did you find a solution? Was your coolant leaking?

 

1. After 10 minutes of running, check if both heater hoses at the firewall are hot.

2. Bleed ALL the air out of your cooling system. If you periodically need to add coolant, then you have a small leak, so fix that.