Thermostat Won't Open

bc56845 · December 22, 2006

I just put a water pump in my '02 5.3 yukon. Everything went fine, but after I filled it back up with coolant and ran it, the thermostat would never open. I drove it about 6 miles, let it idle for about 40 minutes and it never opened. The temp gauge got up to right below 210 and stayed there it never got any hotter. The upper radiator hose and both heater hoses got hot, but the lower hose never got hot. I went and bought a new thermostat and put it in and nothing changed. Is this normal, do these thermostats just take an extremely long time to open or what? Thanks.

redvett · December 22, 2006

If you drove it 6 mi and let it idle 40 minutes and it didnt overheat its working OK unless its -30F and the abient air temp is so cold its keeping the engine cool.

mshell56118 · December 23, 2006

I just put a water pump in my '02 5.3 yukon. Everything went fine, but after I filled it back up with coolant and ran it, the thermostat would never open. I drove it about 6 miles, let it idle for about 40 minutes and it never opened. The temp gauge got up to right below 210 and stayed there it never got any hotter. The upper radiator hose and both heater hoses got hot, but the lower hose never got hot. I went and bought a new thermostat and put it in and nothing changed. Is this normal, do these thermostats just take an extremely long time to open or what? Thanks.

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well the lower hose is coming out of the radiator which is cooling the coolant down and if you are not putting a real heavy load on the engine it might not get real hot. if your top hose is hot then i believe the thermostat is working correctly because if you have a therm stuck open the top hose never gets hot and if it is stuck closed you would have overheated the engine in the amout of time you have ran it

frdfandc · December 24, 2006

Your thermostat is working properly. Coolant flows thru an engine from the bottom to the top. Coolant enters the the enigne thru the lower radiator hose and exits the upper radiator hose. That is why your thermostat is always at the EXIT of the engine, upper radiator hose normaly attaches to it, so the thermostat can control the temperature of the coolant by opening and closing

If your lower radiator hose is much cooler than your top radiator hose, than you getting the proper heat transfer and everything is working properly.