I have an 02 4dr blazer that I bought a few months back. Shortly after I bought it I noticed the heat wasn't working. Well it had the old Dex-cool in it so I figured it was clogged up. So I went and flushed it and got a ton of gunk out. Hooked it back up and I had heat.

About a week later I decided to try it again and same thing no heat. Decided to flush the entire system and get the dex-cool out. I had heat again.

About a month later my water pump went out so I replaced it and flushed the entire system again, heat was working just fine and didn't really get any nasty gunk out from that flush.

Yesterday I decided to try the heat and I have nothing again. So I have new coolant, water pump, and thermostat. There were no leaks from when I flushed the heater core either. So I'm not sure what's going on. Is it possibly a bad heater core even though the heat works right after I do a flush on it?

 

possibly the heater core is just plain clogged. one way to find out is find the two hoses going into your firewall under the hood. after maybe 10-15 minutes of driving touch each of them. now careful cause they will be hot, if one is hot and the other is warm or cold then the heater core isnt allowing coolant to go through.

 

If it's sludged up as bad as you say, someone probably added ethylene glycol at one point in time. Might want to check this out: http://www.ricksfreeautorepairadvice...-wrong-coolant

Basically you need to flush each component of the cooling system separately, in both directions: engine block, heater core and radiator. You might need a cooling system chemical cleaner to remove stubborn sludge. Most auto parts stores have it, follow the instructions on the bottle. This will also remove the ethylene glycol. Fill the system with 50/50 Dexcool and distilled water. If you can't clean the heater core out, you'll need to replace it...if you want heat.

 

If I remember right both hoses are hot. I'll check for sure tomorrow.

Captain, when I say I flushed the system I did do each component of the cooling system separate. So I flushed the heater core by itself and did it reverse flow first then the normal way. Some nasty stuff came out at first but has been clear ever since. It seems to flow just fine as well.

 

Checked vacuum lines? I know you had heat for a short spell each time & probably not related, but they do cause a lot of issues with our vehicles.
It does sound like something is clogged though, but the things we don't consider may be the issue, is all.

 

I was kind of thinking the same thing. Is your system a climate control system or just the manual control.

 

It is the climate control system. I thought maybe a vacuum issue but if it was a vacuum issue wouldn't I not be able to hear it switch? Also, wouldn't it not switch in between the floor vents and the defrost vents? I maybe wrong I don't know much about how all of that works.

 

So I take that back the hose going into the pump isn't as hot as the one from the intake. So that makes me think it's a clog. I guess I'll flush it one more time real good and see if that works.