Won't stop heating up. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

evan · 11-09-2006, 11:20 PM

I drove my truck for the first time in about a week today, and the engine wouldn't stop heating up. I had the heater cranked but it was just blowing cold air. I shut it off and let it cool down and then started it again. The second time it looked like it was going to keep heating past the normal 1/4 of the temp gauge, but then it started blowing warm air through the heater vents and instantly dropped down to the usual temp.

Does that sound like a bad thermostat to you? If it does, what temp of thermostat should I replace it with for normal operation? (It's a .030 over 350)

piecesparts · 11-10-2006, 12:26 AM

I run a 180 degree T/Stat in all of my vehicles, BUT I live in Kansas. You live in "SNOW HELL" and I imagine that it can get cold up there, so you may want a 195 degree T/stat. Also take a look at your timing, if it is set low, that could make you heat up more than you want.

89 crew · 11-19-2006, 06:52 PM

The heater doesn't run through the thermostat. it comes out of the intake just before and goes back in usually to the water pump. for the heater to not blow warm it is usually low on coolant.

piecesparts · 11-19-2006, 10:24 PM

Most of the mid eighties to the later trucks had a line that came off of the intake manifold and went through the heater and back to the radiator tank, that is a truism. However if your engine temp gauge is increasing, but the heater is cold, then a couple of problems could exist.

First---Do you have a normal radiator level? If not then the motor will heat up and the heater will blow cold air, because it is not getting enough water to heat it. This COULD be caused by a leaking cylinder head gasket. If you fill the radiator and the level goes down in a short period, BUT there is no apparent water on the ground, then I would have the radiator checked for carbon monoxide. A good shop can do this.

Second--- a Stuck T/stat would keep the water from going back to the radiator in a normal flowpath, so if it was stuck shut the heater would be getting ALL of the water it could get and then some. I am doubting this is the cause of the heater not working properly. However the T/stat could be stuck, NEVER overrule the obvious. The temp control valve for the heater may be disconnected and you have to look at it to find out.

11-09-2006, 11:20 PM	#1
evan Registered User Join Date: Jul 2005 Location: SK, Canada Posts: 488	Won't stop heating up. I drove my truck for the first time in about a week today, and the engine wouldn't stop heating up. I had the heater cranked but it was just blowing cold air. I shut it off and let it cool down and then started it again. The second time it looked like it was going to keep heating past the normal 1/4 of the temp gauge, but then it started blowing warm air through the heater vents and instantly dropped down to the usual temp. Does that sound like a bad thermostat to you? If it does, what temp of thermostat should I replace it with for normal operation? (It's a .030 over 350) __________________ Evan B.

11-10-2006, 12:26 AM	#2
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: Won't stop heating up. I run a 180 degree T/Stat in all of my vehicles, BUT I live in Kansas. You live in "SNOW HELL" and I imagine that it can get cold up there, so you may want a 195 degree T/stat. Also take a look at your timing, if it is set low, that could make you heat up more than you want.

11-19-2006, 06:52 PM	#3
89 crew Registered User Join Date: Mar 2006 Location: Kansas Posts: 865	Re: Won't stop heating up. The heater doesn't run through the thermostat. it comes out of the intake just before and goes back in usually to the water pump. for the heater to not blow warm it is usually low on coolant.

11-19-2006, 10:24 PM	#4
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Re: Won't stop heating up. Most of the mid eighties to the later trucks had a line that came off of the intake manifold and went through the heater and back to the radiator tank, that is a truism. However if your engine temp gauge is increasing, but the heater is cold, then a couple of problems could exist. First---Do you have a normal radiator level? If not then the motor will heat up and the heater will blow cold air, because it is not getting enough water to heat it. This COULD be caused by a leaking cylinder head gasket. If you fill the radiator and the level goes down in a short period, BUT there is no apparent water on the ground, then I would have the radiator checked for carbon monoxide. A good shop can do this. Second--- a Stuck T/stat would keep the water from going back to the radiator in a normal flowpath, so if it was stuck shut the heater would be getting ALL of the water it could get and then some. I am doubting this is the cause of the heater not working properly. However the T/stat could be stuck, NEVER overrule the obvious. The temp control valve for the heater may be disconnected and you have to look at it to find out.



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