Thermostat -- stuck open? Any damage?

[pow]

The CEL has occasionally been going on and off, and I finally went to Autozone and had the OBDII scanned. I got "coolant temperature below thermostat regulating temperature", which probably means a thermostat that's stuck open. I've been noticing that the temp gauge needle being suspiciously low.

It's been like that for a while... so my question is, was there any damage caused by having a thermostat stuck open?

[Buickfosure]

Not really any damage caused but I would replace it soon, most of the time they fail closed and cause overheating and possible engine damage. Thats why I always run on them failsafe thermostats that fail open since I've had some bad overheating experiences due to a thermostat failing.

Edited February 25, 2007 by Buickfosure

[loki]

if it's newer than an 80's model, just check your butterfly valves for carbon build up...

[Buickfosure]

One other thing to think about before replacing the thermostat, that code could possibly mean a malfuctioning coolent temp sensor as well so I would look furthur into it or take it to a shop if you don't feel like wasting time and money replacing the thermostat only to find out it was just the coolent temp sensor all along.

[pow]

One other thing to think about before replacing the thermostat, that code could possibly mean a malfuctioning coolent temp sensor as well so I would look furthur into it or take it to a shop if you don't feel like wasting time and money replacing the thermostat only to find out it was just the coolent temp sensor all along.

Hm, that seems very possible, too. But the gauge still appears to work... the needle just takes longer than usual to reach the middle. Or could that happen and still be misfunctioning?

[daves87rs]

One other thing to think about before replacing the thermostat, that code could possibly mean a malfuctioning coolent temp sensor as well so I would look furthur into it or take it to a shop if you don't feel like wasting time and money replacing the thermostat only to find out it was just the coolent temp sensor all along.

I was thinking that too..

[2005 EquinoxLS]

I would try replacing the thermostat first. Then see what happens. My parents Equinox did this and it was the thermostat. Dad had noticed it didnt seem to heat as well as normal.

[RoadmaSSter]

empowah

But the gauge still appears to work... the needle just takes longer than usual to reach the middle. Or could that happen and still be misfunctioning?

The dash gauge can have its own temp sensor/sending unit that is completely separate from the engine coolant temperature (ECT) sensor which is there to communicate with the car's computer.

So yes, the dash gauge can be functioning properly even with a bad ECT sensor.

In my '95 Caprice for example, the ECT sensor is located near the water pump while the sending unit for the dash gauge is located in the pass. side cylinder head. I have an intermittent failure condition with the ECT sensor which is setting the CEL and causing the computer to switch both cooling fans to run (a fail-safe to protect from overheating while it is not getting a signal from the ECT sensor and a big clue to a bad ECT sensor) all the while the thermostat and dash gauge are functioning normally. I just need to get a new ECT sensor and put it in, but its cold out and it is not yet acting up everytime I drive it.

I would guess it is your thermostat first, but it could also be the ECT sensor. Anyway, hope you got it sorted out.

Edited February 27, 2007 by RoadmaSSter

[pow]

The dash gauge can have its own temp sensor/sending unit that is completely separate from the engine coolant temperature (ECT) sensor which is there to communicate with the car's computer.

So yes, the dash gauge can be functioning properly even with a bad ECT sensor.

In my '95 Caprice for example, the ECT sensor is located near the water pump while the sending unit for the dash gauge is located in the pass. side cylinder head. I have an intermittent failure condition with the ECT sensor which is setting the CEL and causing the computer to switch both cooling fans to run (a fail-safe to protect from overheating while it is not getting a signal from the ECT sensor and a big clue to a bad ECT sensor) all the while the thermostat and dash gauge are functioning normally. I just need to get a new ECT sensor and put it in, but its cold out and it is not yet acting up everytime I drive it.

I would guess it is your thermostat first, but it could also be the ECT sensor. Anyway, hope you got it sorted out.

Interesting. Thanks for the help!

A few days ago, after switching the engine off and removing the key, the cooling fan turned on by itself. I thought that was odd as it never happened before, so I switched the car on and off again, and that shut if off. The engine compartment wasn't very hot at all.

During normal driving, however, the fans seem to be fine. It only goes on high-speed (and consequently making a garbage truck sound) when the A/C is on while idling for a while.

Edited February 28, 2007 by empowah

[76ChevyTrucker]

Yeah, normally the Coolant Temp Sensor signal below regulating temperature means that the CTS has gone haywire. More times than not, its located next to the Thermostat housing, so if you really wanted to, you could always slap a new thermostat into place whilst your at it.