Alright Quick question, I have a 2002 Blazer LS 4x4 and the temp gauge keeps running hot, it started to run hot only after driving it then shutting it off for a few minutes then turning it back on, the temp would go up immediately. Once I started driving it would decrease to the normal running temp. Now it still does that but it also shows that it is running hot every once and a while, when driving. Something else that might help, If my heat is on, and I stop at a red light, I lose all heat after a couple seconds. Thanks in advance for any help.

 

First, check your cooling fan clutch by spinning the fan by hand with the engine off. If it doesn't spin freely, you have a bad clutch that needs to be replaced. How's the coolant level? Have you had the coolant drained and flushed anytime recently? If not, that and a new thermostat could be in order. If you have changed the coolant, then you may have air in the system that needs to be purged. The part about the momentary heat loss could also point to a heater core going bad.

 

coolant temp sensor if its really not running hot, rriddle3 makes good point on coolant level and air in the system, if that is the case what is happening is as the coolant flows through the heater core, the air in the system is reaching the core and as the blower motor runs thehot airinto the cabin, the hot coolant is not heating the air as it should because its not contacting the coolant, its contacting the cooler air in the core, when you speed up and the water pump moves the coolant faster through the system the air being blown is hitting the coolant and heating the cabin, if this did not make sense i will try and put it more simple but i do hope this helps ya out, best of luck to ya let me know if this works!

 

Yah it could be that thermostat sticking, the better ones fail open so they dont cause and overheat. It seems like if it were air in the system it would have made its way out, since you didnt mention opening the system recently.

 

With out having the time to reply to the post, I will when I get out of work. I have an update, I changed out the thermostat last night since its cheap and easy, the temp gauge now goes hot while driving, and when it does go over 210 I start to loose heat again, on the way the work it hit the red and I lost all heat, which had me worried, but almost at the same time it hit the red it started to drop back down and I again had my heat. I dont know if any of this helps in figureing out what the problem is. I also have a slight odor of coolant. Thanks for the answers given so far, they are opening a couple ideas in my head.

 

Ok with the smell I lean toward rriddle3 more about the heater core leak, although its always possible its a combination of issues. We can basically rule out the thermostat unless it was defective. If you have a OBDII scanner that can check coolant temps or know someone with one it might be worth checking. Im not sure about 2002's but in 97 the temp sender for the gauge is different then the one for the computer.

 

i agree, check the heater core. air in the system creates dex-cool sludge and could clogg it up, the smell kinda make me think that also. normal clean coolant should have a sweet smell. with having a smell, sounds like a leak in the heater core.