I had this same issue a couple of years ago. I flushed my core out with CLR and the water came out black. I flushed it and then back flushed it until the water came out clear. I have had good heat ever since.

 

#1. First make sure the cooling system is completely full. First thing in the morning, take the radiator cap off the radiator and actually look. It should be completely full to the brim, having filled itself upon cooling by sucking coolant out of the coolant reservoir. If not, fix and retest before going on. Note that it may take several heating/cooling cycles to get out all of the air.

#2. Second, make sure engine is getting up to temperature. What does the gauge read? If you have a 195 thermostat, the gauge should read 195. If not, fix before going on.

#3. Third, make sure heater core has adequate circulation of water through it. Both hoses hot to the point where you can't tighten your hand around them. If not, fix before going on.

#4. Only then start jacking with the blend door.

I suspect your heater core is plugged from running the cooling system with air in it. This is what makes the brown goo in our Blazers. If you flush it, back flush it with regulated pressure and don't put use full house water pressure (which is about 40-60 psi IIRC). If you try to flush heater core, be prepared for it to start leaking dramatically onto your passenger floor and therefore need to be replaced in order to drive. It's the risk you will be taking.

You should also consider where your coolant is going and why you need to keep adding. If it is from a leaking lower intake manifold, you can easily ruin the engine by getting coolant in the oil.

Good luck and best wishes for a successful repair

 

I guess I'll chime in with my heat problem now. I've had this issue for a few years now and am out of ideas. I have a 1997 Olds Bravada.

1) Thermostat replaced. 195 installed. Verified operation in pan of hot water before installation.
2) Heater core and heater hoses was replaced when heater core started to leak.
3) Both heater hoses get hot.
4) Blend door works correctly.
5) Fan clutch replaced (it was stuck on).
6) Water temp only at 177 even after driving for 10 minutes or idling for 15 minutes @ 40 degrees outside temp. Used laptop to read PCM. Dash gauge shows about the same temp.
7) Coolant is full.
8) Flushed heater core. Water was clear and full flow in both directions.
9) Upper rad hose is getting hot - not sure why if water temp is only 177. Therm shouldn't be open yet.
10) Small amount of heat coming from rad. Again - if water temp is only 177, therm shouldn't be open yet.
11) Heat at vents is only 105 degrees.
12) The only time that I've seen the temp gauge go to 210 is when it was about 80 degrees outside. Then I have a decent amount of heat.

Anyone? I'm stumped and out of things to try.

Thanks,
Tim

 

It's not nice to hijack someone else's thread. Please start your own with what you wrote here.

 

Finally. We had 2 weeks of below zero weather and couldn't do anything till now.
I bought the new Air Door Actuator, got the 2 diff size sockets and tools and started.
Right away we (buddy and me) got stuck trying to swing the air duct controller out of the way so we can access the actuator. The way described in your video does not seem to work on mine. It looks like air duct controller is built just a little diff. Can't move it up or down or sideways. Am going to try to attach couple of photos + there's old thread in this forum showing same pics of a 2000 Blazer like mine.







pics in this old thread are what mine looks like also

https://blazerforum.com/forum/2nd-ge...e-69344/page2/

 

Am going to take a closer look at coolant level and thermostat reading as per your suggestion. Am already in the process of replacing the actuator
since i had already bought the part.

 

I feel you pain. I have great heat for about 20 minutes and then it just randomly starts blowing cold. If I turn it to cold and then back to hot it works fine again, or of I turn the car off and back on it is fine. The coolant is full and the engine gets between 188 - 194 degrees. So, it is a mystery.

 

Had this same issue, but after flushing a ton, and a new thermostat, works great! I get a water sound from the heater core now, so trying to get the air bubbles out. Not having any luck though. Any tips? (Not trying to hijack, but I can't post, so trying to get cred, haha)