Hi. I am trying to figure out why the engine is overheating, and heater core is not supplying any heat.

When cold start, after few miles, I got heat from heater core, but when the temp gauge reaches cca 200, suddenly no heat from heater core. Also the temp raises more. I thought it might be bad thermostat, but I changed it 1 month ago, during head and intake gasket change. I preventively ordered another thermostat and radiator cap, because when the temp gauge reached 3/4, the cap let the water go out to the overfill tank.

I wanted to start from beginning, to be sure, that hoses to the heater core are plugged fine, but I did not found the scheme, or diagram. I am looking for something similar to this, but for Blazer. I am looking for it for two days, but still nothing found. Thank you for help!

Sorry for my bad English, I try to do my best :-)

 

Can you please specify the model and year of your Blazer.
Eventually also the engine version.

 

Hi, sure:

it's Chevrolet Blazer year 2000, 4,3 V6, 142 kW, vin W, engine code L35

Thanks!

 

Try a search with "illustrated parts catalog - cooling system"

maybe here: https://www.gmpartsonline.net

 

In addition:

-check routing of the serpentine belt (the owners manual should have the correct routing or a sticker under the hood.)
- check for leaks, also from the heater core (passenger foot-room behind/below carpet - leaking cores will dump the water behind the carpet most of the time).