How do I test the Coolant Temp Sensor?

[DennisG01]

Concerning the Coolant Temp Sensor in the T-stat housing - can it be Ohm tested? What would the appropriate reading be? Will the reading vary depending on temperature?

I recently replaced one and immediately got better fuel mileage, but I was just wondering how to actually test the sensor.

[ 01-30-2006, 07:18 AM: Message edited by: Dennis Galligani ]

[JohnC]

T(F) resistance
210.....177
194.....241
176.....332
158.....467
140.....667
122.....973
104...1,459
86....2,238
68....3,520
50....5,670
32....9,420
14...16,180
-4...28,680
-22..52,700
-40.100,700

[ 01-30-2006, 10:25 AM: Message edited by: JohnC ]

[DennisG01]

Thank you, John! That was exactly what I was looking for. Do you use a thermometer and stick it in somewhere (get your minds out of the gutter :D )? Where do you take the temperature readings from?

[stingthieves]

I suggest using something like a Raytek non contact thermometer and read in the same spot as or right next to the sensor - Kind Regards - Rick

[rlvelin]

When I tested mine, I didn't have a non contact thermometer so I pulled the sensor and screwed a plug in its place real quick to avoid loosing too much coolant.

Then I stuck the sensor in a small pan of cooking oil on the stove (water will only get up to its boiling point unless you add a bunch of sugar or some antifreeze, even then it might not get to 210 F unless under pressure). A thermocouple was used to measure oil temp, a thermometer would work fine but keep it off the bottom of the pan as the pan bottom will be hotter than the oil and measure resistance.

[DennisG01]

Would a contact thermometer work? A friend has a voltmeter with a temperature probe attachment...

That's a good idea about boiling it - you'd know exactly what temp it is.

[rlvelin]

Measuring the temp of the head right next to the sensor either with a contact or non-contact thermometer will probably not be very accurate. The temp of the metal right there will be lower than the coolant temp since the coolant has circulated through engine and picked up heat throughout and the outside surface is being cooled by the atmosphere.

One thing I was going to try was to remove the bleeder screw fitting and temporarily put in a compression fitting that will fit the temp probe on the voltmeter like your friend has (its a thermocouple in a metal sheath). You shouldn't loose too much coolant this way, it would be pretty quick and easy once you find the right fitting, and you just need the one multimeter to first measure temp and then ohms through the sensor.