I have a 96 blazer with 91,000 miles on it. I was driving to work today an noticed the heat quit working an the temp gauge was rising. It jumped almost to the red. I pulled over an shut it off an checked under the hood. Everything felt cool an there was coolent in the system. I started it back up an the gauge stayed around 210 than started to climb again an them went back to normal temp an I got heat again an the temp stayed normal. What could have been the problem? I haven't changed anything recently on it. Thanks for any help

 

sticking thermostat or air pockets in the system. Or both. Check fluid level

 

I changed the thermostat an it didn't solve the problem. The temp starts to get close to the red than it drops back down to normal temp an runs fine. The top hose is hot an the bottom hose is cool an there is plenty of coolent. I wonder if I should have the system flushed

 

So I have been driving it around the housing plan an the temp will rise fast an the check gauge lite comes on for a couple seconds, I stop an it drops to normal temp than it goes back up to 210 whenni start driving an stays there. In afraid to drive it to far incase something worse happens. Any ideas anyone?

 

did you purge/bleed the system? could be your water pump or belt slipping. but try bypassing the heater core first and see if that takes care of it.

 

I can't say for sure, but I've had the water pump done on both my blazers I've owned around 100k-125k miles. Yours might have gone early. I think it would make the most sense, as your temp rises as you drive rather than drops, so fluid and airflow don't seem to be your problem, but perhaps it isn't circulating the coolant.

 

It sounds like the heater core may be plugged up. I would back flush the core and see if that helps.

 

Thanks for the info, I'm gonna flush the heater core an see if that helps an if it dosent the next thing I will check is the water pump. An the temp will drop an rise as I'm driving. It will get real hot than go down to normal temp than go to 210 an stay there than drop again all while driving.

 

I had the same problem. I flushed the heater core, replaced the thermostat, and flushed the cooling system. That seems to have taken care of the problem.

 

Well I flushed the heater core an not to much junk came out before the water ran clear. I also changed the upper hose an added coolant till the rad was filled an everything works great now. I'm not sure what the problem was but it's fixed now. Thanks everyone for the help an giving me ideas on what it could be.