Which temp sensor to believe?

[thor124]

Hi Folks,

I've got a 1998 Astro, around 250K KM on it. I've noticed as of late that the temperature reading on the dash is around 25-30degreeC LOWER than the one pulled from the ECU.

I know that there are two sensors, one for the computer, one for the dash. Is it normal to have such a difference between the two? Which should I believe?

[chevymaher]

I would start it cold and put a thermometer in the water. Check it against both reading after it hot. See which one is right.

[thor124]

I'm leaning towards the one feeding the ECU being fubar.

The van sat for around 18 hours before I left for work this morning. It was 14 degree C ambient. Prior to starting the van it was reporting a coolant temperature of 24 degree C.

I know that's not "conclusive" proof, but for the cost of the sensor and a little antifreeze, I'll change it out.

[RECox286]

These sensors aren't hooked to something being sent into space. How accurate do you want for a relatively few dollar part ?

Especially since the youngest of these trucks is nye on to 8 yo, and the average is more like 13 yo. How many is that in people

years ?

Uncle Bob

[redfury]

I had the exact opposite problem, but it was because I put pipe thread tape on my new dash sensor which of course screwed up the grounding of it and made it read high. The sensor up top might just have some corrosion in the threads which is causing the resistance to go up for the ground and cause it to read high automatically.

[Phantom]

I'm leaning towards the one feeding the ECU being fubar.

The van sat for around 18 hours before I left for work this morning. It was 14 degree C ambient. Prior to starting the van it was reporting a coolant temperature of 24 degree C.

I know that's not "conclusive" proof, but for the cost of the sensor and a little antifreeze, I'll change it out.

Since the dash gauge gets its reading from the sensor mounted in the head ; by what method did you use to determine the temp reading of the ECM temp sensor when the engine is not running ?

[redfury]

That can be easily done with a simple scan tool that can read live data...Or a smart phone with Torque and a bluetooth dongle.

[Phantom]

That can be easily done with a simple scan tool that can read live data...Or a smart phone with Torque and a bluetooth dongle.

I agree ,, just wondering which tool or method he actually did use

I like to keep notes and document causes and findings in various cases ,, including other peoples cases