Coolng problem or bad gauge/sensor

[Jacko]

Cooling problem or bad gauge/sensor

Lately the temp gauge on my 97 Sport steadily heads towards the red mark. If I remmeber correctly, the oil, voltage and temp gauge drop to the bottom when the engine is turned off. But now, the temp gauge stays where it's at. It will drop down when I start the engine again hours later when the engine is cool. Is this a cooling problem or is it a bad sensor or gauge?

There is no coolant leak and the radiator/fan/clutch/water pump seem to be fine. Anyone have any experience with this? Thanks in advance.

BTW, did a search and didn't find any posts regarding temp gauge getting stuck when the engine is turned off.

 

[mrboyle]

Does it only do it with the engine running (and just stay where it was at once the engine is shut off)? If so don't sweat it, this is common with electronic guages. As for the temp going into the red, when was the t-stat last changed?

 

[thewishkah]

Yeah i would lean toward the thermostat not hard to change and usually is the most common reason for the temp guage to go into the red and stay there till its cool

 

[Jacko]

I tried to change the thermostat(which has never been changed on this 67K mile truck) but couldn't get to the last 2 bolts holding in the thermostat housing(the upper intake manifold was in the way and I didn't have enough time to remove it) so I just flushed the system and changed the coolant. I guess I should just go ahead and replace the thermostat, the part is cheap enough and it won't be as much of a hassle as having to be chauferred around.

If I understand this correctly, this is why I don't think it is the thermostat. First, when the engine is cold and started and I squeeze the coolant return hose running from the thermostat housing, it is cold, soft and not pressurized from flowing coolant. Therefore I assume that the thermostat is in the closed position. Then I drive around the neighborhood until the gauge gets to the very hot range and I double check by turning on the heat until I can confirm it's blowing hot air. Then I park the truck and with the engine still on, I feel the coolant return hose. This time, it is warm/hot, pressurized/stiff, so I conclude that the thermostat has opened and the coolant is flowing to the radiator. A slow squeeze and release of the hose allows me to feel the coolant flowing back into the radiator so that must mean the water pump is ok. This leads me to think that either the gauge is bad or the temp sending unit(s) is/are bad.

Any ideas to confirm this before I go and change the units? Also, I don't have a voltmeter but maybe that's what I need to get. And TIA to those posting.

To clarify the problem: the temp gauge rises close to the red zone but the needle does not drop down when I turn off the engine (like the voltage and oil pressure gauges do.) It will stay in the same position as long as the truck is not started. Once the engine is cool and it's started, the needle will finally drop down. I could just ignore it, but I don't want to risk major engine problems from this.

 

[thewishkah]

ok in that case your right it doesnt sound like the thermostat but i think that what it does might almost be normal cause when i turn my truck off the needle stays put for a few hours till it cools down but i think it drops down by its self i dont think it has to be restarted