A pyrometer is good to read where the coolant is hot and not traveling, this may help diagnose where or why you have a lack of heat.

 

I had this same exact problem, it's a problem with the Heating Core. You must pull out the core under the hood and clear it out with a high-pressure air hose, it is clogged. After that, put the core back, and start it up. After a few moments, hot air should blow again!

 

Hey Guys. I have an 01 Blazer that Im having some heat issues with. I am not seeing any evidence of any leaks anywhere. The first thing I am noticing is that the inlet hose to the heater core is hot, and that the outlet hose is cold. This made me think heater core, but the hot hose doesn't seem to have any water flowing through it. That made me think that the heat could be from steam rather than water, and that the problem might be with the water pump. I have seen no sign of a water pump malfunction otherwise, so now I'm alittle lost. You guys got any suggestions?

 

I just cured a simmilar problem on my 1999 S10. I changed the thermstat which didnt really help much, checked the door activation by having blower running then switching from cold to hot and could eliminate that. So finally I could see one hose going into the matrix was cold and one hot so disconnected the two hoses going into the heater matrix at the engine side of the bulkhead, connected a piece of hose to the hose on the right hand side and blew hard through it till some black gunge started dribbling out, I then connected up a garden hose to the left side and ran water through the matrix at the mains pressure for about 15 minutes till it ran clear. Connected back up and had heat like never before!

 

Big Allan Welcome to the forum.

 

Thanks, I may be in UK but a serious chevy fan with three chevy race cars one I am renovating which is a genuine 77 Tubeframe Penske IROC Camaro race car imported here in the early 80's and one of 15 and two road chevys.