Chevy techs, please put your thinking cap on.
 

I have a 1998 1/2 ton GMC Savana with a 5.7 vortec.. At 120,000 miles, the intake gaskets leaked water. After changing the gaskets, the leak is gone but the motor will not get to normal operating temperature. We have changed the thermostate 3 times with the correct style 190. degree for the vortec. The oe temp gauge climbs to 200 degrees, the thermostate opens and it drops to 140 degrees. It will do this all day long. I have cardboard in front of the radiator. The radiator hoses never get over 170 degrees there fore the heater never works. The heater control valve works properly with a vacuum pump attached. I live in SoCal where most days are warm. Any thoughts??

Re: Chevy techs, please put your thinking cap on.
 

Could the heater core be plugged?:confused:

Re: Chevy techs, please put your thinking cap on.
 

Checked that Lonnie, water does flow freely thru the heater core.

Re: Chevy techs, please put your thinking cap on.
 

Does the return heater hose go to the radiator? If it does, there should be a restrictor in the hose.

Re: Chevy techs, please put your thinking cap on.
 

My 1996 Chevy has done the exact same thing since I bought it new in March 1996.
Mine has the towing package and engine oil cooler also.
I questioned GM about it and was told that was normal until the engine has a load to pull and work the engine and cooling system.
I have 104,000 miles and still going strong.
On a hot day in TX it will stay constant about 190 on the gauge but when it is cool it is up an down on the gauge from about 140 to 190. I have not ever checked the heater temp but it seems to warm the cabin ok even when it is really cold.
It is just working the thermostat.
My Experience
Rick Cates

Re: Chevy techs, please put your thinking cap on.
 

sounds like an air pocket to me. i fought an s10 one night for 2 hours trying to make that stop. i finally took one of the heater hoses off and lightly blew air through it with my compressor and problem quit. also you may check the radiator cap or buy a new one i know when these things act up they can do goofy things. i kept blowing tanks on radiator in my 88 chevy 3500 with a 7.4 over a stupid $5 radiator cap

Re: Chevy techs, please put your thinking cap on.
 

Heater control valve works properly and the core is not plugged as water flow freely thru it. Seems to me if it had air in the system it would overheat. The last thermostate was installed 8000 miles ago. I would think all of the air has been burped out by now. I use a laser beam digital point and shoot thermometer gun to determine the water temp at many places on the motor, heads and radiator and hoses. Has always been below what you would call normal ever since the manifold gasket change.
No return hose to the radiator Billy. But I do agree that the system needs a restriction to slow down the water flow, keep it in the block longer to get hotter.
Has a new 3 week old cap on it. An OEM 16lbs cap that I pressure checked so I know it holds proper pressure.
I appreciate the ideas and thoughts, please keep them coming.

Re: Chevy techs, please put your thinking cap on.
 

Do you have an electric fan and does it go on and off? what about a stuck fan clutch, Im still thinking. Pull the thermostat and put it in a pan on the stove and see if it opens and closes at the right temp.with a good temp gauge:confused:

Re: Chevy techs, please put your thinking cap on.
 

Any chance the wrong gaskets were used? Alot of the intake gaskets have a restrictor made into them to properly route coolant. There typically is a Frt. and back to the intake gaskets, if installed backwards it may cause the issue you describe. Joe

Re: Chevy techs, please put your thinking cap on.
 

i agree with this theory,also is your temp actuator opening the door to allow air to flow through the heater core
scott fifield