Car:
2004 Blazer 4wd. 136ish miles.

Problem:
Overheating in stop and go traffic- up to about 235 degs then I stopped and pulled over. I tried to turn on the heat to cool it down, and nothing. The air was blowing out the vents but it wasn't hot. Not sure if this is connected or a separate issue, I've only owned her for about 2 months now so haven't tried the heat before. Also, I've noticed if I turn it off and then come back a few minutes later, the temp would be hotter than when I turned it off.

I checked water/coolant level. It's normal, but it's got floaties in it so I'm sure it needs a flush. I also lightly touched both coolant hoses and it seems they were both hot so not sure it is the thermostat.

Any info would be great! Thanks for reading yall.

 

well you def have a flow issue.
i would flush and replace thermostat...sound like it is stuck shut.
you can try tapping on it...but that is a temp solution to get you to the store to get another thermostat.

while your at it i would flush the heater core separately..they like to plug up

 

X2 on the definite flow issue.

And to answer your question, yes the no heat and over heating is related. Coolant gets pumped from the water pump into the heater core and you either have no heat because the heater core is plugged or something is wrong with your water pump. And because your engine is over heating as well i would guess that the water pump is not pumping fluid. weather that is from a faulty water pump (which very rarely happens on these engines) or a blocked line, air bubble or low pressure (all three common) is what you need to figure out. And if your thermostat was stuck closed you would still have heat so i dont think that is the issue (still good to check).

For now i would do a coolant flush and change the thermostat. First before you do anything tho, idk if you did this already but check to see if the radiator cap is tight. Really obvious but if its loose it will cause your problems. Also when you say you you checked the level did you just look at the over flow tank or did you look in the radiator also? With the engine cold take the cap off and look inside, if its dry then thats a problem. probably due to a faulty cap. Happened to my other Blazer.

Oh and your other question. the temp rises when your engine is off because it doesnt have any coolant flowing through to take out the heat so it will continue to heat up for a little bit. Which leads me further to believe you have a bad rad cap because if its loose the coolant wont get pushed around very well and none will get sucked out of the over flow tank. i still recommend a flush and thermostat change. just a smart thing to do.

Hope this helps

 

I took the cap off and looked in. And the cap was a b**** to take off, like really tight on there. It was full, but again, had some floaters.. Pretty nasty. I was thinking of changing the thermostat anyways, cheap insurance. I'll try the flush once the weather clears up today.

Alright bought the stuff to flush the system and a new thermostat. But, I can't find the damn drain plug on the radiator! I tried to take the lower radiator hose from the block and couldn't get that beast off either. Someone help! I've looked at pics online and none seem to be similar to what I got...

**UPDATE**
I just worked on er. I never did find the drain for the radiator. I ended up taking the thermostat housing hose off and just ran water through it until it looked clear. It was a blood red color almost. Idk wtf was in there. The used some flush and ran it. Let it cool, then filled with water and let run again. The heater core was still clogged so I just used a hose and blasted all the crap out.
Ran fine, no overheating. And the heat works! Which I don' care about now, but come December I will. I feel accomplished.

 

the drain on the rad is on the bottom corner of the pass side...on the face towards the engine....i know to late, but maybe later on it will help.

anyways....glad to see you have your ride healthy again.
when i replaced my rad it was the same way...lots of reddish grime and floaties.

 

Nope, no drain. I swear. I'll try to upload pics. Idk if the radiator was replaced at any point but no drain. Trust my, I checked, rechecked, checked, rechecked... Piddled, checked, and rechecked thinking HOW DID I MISS IT?! No drain.

 

GM ditched the drain for one reason or another on the newer trucks. I can't remember the exact year they did it, but you aren't crazy. You either have to siphon out the coolant or pull the lower hose & let-r-gush!