I'm at a loss here, hoping someone has some advice. 97 blazer 4.3 auto. Had a cracked heater core and blown intake gasket. Replaced intake and head gaskets along with the heater core. After said work, still over heating. Replaced thermostat, water pump and radiator, did a flush, still over heating. Did a Chem flush checked all the hoses reassembled with yet another new thermostat, same problem. Odd part is while it's sitting still it's fine, temp levels out and blows heat fine. When I'm driving on the other hand I can feel the blower go cold and temp rises pretty quick to 240ish. Pull over and park it and the temp slowly goes down and occasionally drops quickly to about 140, at which point I get heat back. Done the full flush including pulling the plugs on the bottom of the engine. Any thoughts?

 

Overheating can ruin head gaskets and crack heads. Sounds like might be getting combustion gasses in cooling system. Either that or you never got it completely full of coolant. Pockets of air or combustion gasses will not cool the engine or give you heat at the heater core.

 

Block test came up clean, and I'm sure I've had all the air out of it. When it overheats it purges out of my reservoir, but was thinking that would be normal for an overheat condition.

 

Are you installing the thermostat backwards?

 

Hehe, nope...Promise. only thing I can come up with is a stubborn clog in the block somewhere.

 

Are you using the correct Coolant concentration? Other than that I would put money on a blocked coolant passageway :P

 

Using 50/50 dexcool. Coolant flow through the block seems complicated. Previous owner stuffed a lot of stop leak through it. Any suggestions on how to flush just the block and what chemicals to use?

 

Have you tried a reverse flush with just water?

 

Yep, even pulled the radiator and flushed it real well.

 

The blockage would be in the block probably in the lower side of the block in the back but if you're lucky it'll be easy to flush out with dish detergent