Lumina '92 3.1L Euro: Temp Gauge running Hot, but engine not

Hi Everyone !

Sorry for my english, English isn't my first language.

I have a Chevy lumina Euro 3.1l from '92.
I have a little problem with it:

My temp gauge, in the dashbord, says the engine is getting to hot.
When the car is in idle, the temp gauge will just keep rising to around 190-200 F, when driving 2-3 miles, it will keep going up to 260 F and the heat indicator will start flashing.

When we measure the engine's temperatur with a IR termometer at the thermostat house it says 180 F, so the thermostat and the fans work just fine. (the fans kick in when getting over 180)

We have tryed replace the temp sensor twice, but getting the same result/problem.
The problem just came out of nowhere.

Does anyone have a clue to what we could try?

Thank in advance
Thomas

Does your vehicle have two temp sensors?

If it does, there will be a two wire temp sensor(input for the ECM) in the front of the engine(under therm housing), and on the opposite side of the engine, there will be a guage sensor, with a single green wire coming out of it......could be a bad gauge sensor.....

What would confirm this, is if you had access to a scan tool and read engine temp data, and compare it to the reading on the gauge....if ECM temp data is ok, and gauge reading is high, possible gauge sensor, or worse case scenario, a cluster problem...

Hi Tech!

Thanks for your reply,

The engine have 2 sensors, it is the one to the gauge i have changed :)

I have read the temp. with a IR termometer, and he engine temp is fine :)

Those fans don't come on at 180F......they come on at around 218F, I think....sure that IF is accurate?

Were you losing any coolant?

Infrared-sensing "temperature guns" have a dirty little secret. Different materials give off different amounts of infra-red energy. This is called the "emissivity" of that material.

Very few IR temp guns have an adjustment for emissivity. They're calibrated with some "standard" and then the end-user tries to use the temp gun on something that has different emissivity and gets a WRONG READING on the temperature read-out.

http://en.wikipedia.org/wiki/Emissivity

I think your temp gun is reading low, because the fans should not run until the engine temp is somewhere around 220 degrees, not 180.

Beyond that, if the wire to that temp sensor is grounded--for example, if the insulation is rubbed-off the wire somewhere so the copper conductor touches ground--the gauge will read high temperature. That'd be worth looking for.

Hi thanks for reply ! :)

I think the IR is working fine, i can feel on the cooling hose the thermostat open and close, when the IR read aruond 180 F.

I havent loose any coolant at all :)

I will check that wire, but if it was that, the Gauge will raise straight op to 260 F immediately and not wait until i drove a little bit?