Hi All. My 96 Blazer has been running fine. Heater working properly. This is 4.3L
Monday it dropped down close to -30F In northern Minnesota. I could have guessed it wasnt going to start. It didnt, I flooded it.
So I picked up a Zero start Lower hose heater last night.
Today I had to do a few things to get it going again. Change the oil put in new plugs and install that Hose heater. I cut the lower Radiator hose in place. Then had to remove it so I could install the heater. Got the end off the radiator after a little wobbling. Off the water pump. No luck. It was -15 below today as I worked on it in the driveway. I had to go a snag my wifes hair dryer to warm the hose connected to the water pump. After 5 minutes i was able to remove it finally. I brought everything inside so I could put it together in the basement. 1/2 later I reinstalled the hose.
I poured the coolant back in to the radiator. The little bit left over i put in the overflow.
I got in and it fired right up. Temp started climbing. Im running a 170 TStat. So when it kept climbing I started thinking I have an air bubble. Cool air coming out of the heater. My driveway has about a 12 degree slope. So i figured its a good angle to get any bubbles out.
Return line to radiator is cold. Engine was up to about 230 when i shut it off. Ive let it cool and tried again... hoping the air bubble is working its way out. Is my water pump cavitating? How do I get this air bubble out? Pop off the TStat housing?? Or is there a bleeder Im missing?

Thanks in advance.

 

There is a service bulletin that addresses your symptoms (overheating while blowing cold air from heater). It states that leaving the same Dexcool (which is the only type to use) in the system in excess of 32,000 miles can cause formation of rust like material in the colling system. So I guess it could be possible that the work you did might of knocked some of that loose and caused come blockages. The bulletin starts off with a complete flush of the cooling system. But it also states that it is important that there is no air in the system. I would start simple first anyway. If I was in your shoes I would start by elevating the front passenger side of the vehicle as much as possible. Remove the radiator cap and run the engine (if the level is low in the radiator, top it off first). This might burp any air bubbles out of the system. Keep an eye on the coolant and refill as needed. When the thermostat opens you should see the coolant moving.

 

did you put your old antifreeze back in? wonder if its just crappy antifreeze. i actually over heated my 86 chevy 2 days ago when we had -43 windchills. i figured this would be the one day it would overheat. so bought a new thermostat, hoses for the heck of it and all new coolant. when i drained what little that didnt bubble over out of the truck it just looked like muddy water, which is strange cause i just put this engine in like 3 years ago.

it kinda did the same thing when i started it up after fixing everthing, temp was like 170 and upper hose was freezing, but soon as that thermostat opened up it warmed up.

so it could be a thermostat, bad antifreeze , or a air bubble or all 3. thats why i replaced everything i wasnt taking any chances, even replaced my cap

 

I'm having a similar issue. 2000 Blazer, 150,000 mi. I replaced the thermostat, water pump and radiator, all new dexcool, this summer. During this cold snap I've been using my heater, I live in New Orleans, which blows cold air and causes overheating. If the heat is off, no problems. As soon as I turn the heat on, it blows cold andthe engine temp starts increasing drastically. Any suggestions?

 

I don't want to post all the instructions (there's a lot of them) in the technical bulletin for dealing with this because it come from the subscription site ALLDATAdiy.com Leading Source of Factory Automotive Repair Information I don't if there's some type of clause in the user agreement that would state I can't post it or not. But I would recommend going to the site and buying a subscription for your vehicle. It's only about $25.00 per year I think. If you do subscribe, you will see a link for "All Technical Bulletins". According to the vehicles it applies to, 2000 Blazers are effected also.