Engine Temp Sensor and overheating

lilmatty · **Posted:** Wed May 17, 2006 8:17 pm

Hi. Anybody got a 'backyard mechanic' way to test the coolant temp sensor?

My 02 has a situation where the temp guage will sometimes rise up into the red and even sound the warning chime. Yet when I pop the hood the engine is cool; if it was really overheated I should get a balst of heat from it. No such thing.

Looking for ideas but am now thinking it's a bad sensor.

2006KJSPORT4x4 · **Posted:** Wed May 17, 2006 9:54 pm

thermostat might need replacing and check your intake manifold for a leak or breach...my dodge avenger used to do that and then the engine eventually died before I could get the intake manifold replaced....temp gauge go way up then back to normal...crazy....good luck finding what it is exactly

lilmatty · **Posted:** Wed May 17, 2006 10:20 pm

I would think that a thermo sticking shuit would cause the engine to get really hot. My engine doesn't get hot.

Edwin · **Posted:** Wed May 17, 2006 10:38 pm

Have you checked to see if there are any codes being throwed out?

lilmatty · **Posted:** Wed May 17, 2006 10:41 pm

P0837. See my post below on that one. Seems unrelated.

krazz1e · **Posted:** Wed May 17, 2006 11:37 pm

sounds like a false alarm for sure, but you may want to throw an aftermarket temp gauge on and just confirm that. If confirm then why not just replace the sensor?

valvestem · **Joined:** Thu Jul 07, 2005 7:01 pm **Posts:** 222

lilmatty wrote:

Hi. Anybody got a 'backyard mechanic' way to test the coolant temp sensor?

My 02 has a situation where the temp guage will sometimes rise up into the red and even sound the warning chime. Yet when I pop the hood the engine is cool; if it was really overheated I should get a balst of heat from it. No such thing.

Looking for ideas but am now thinking it's a bad sensor.

There should be a way to put an ohmeter on it to check the resistance to tell if it is bad. The following is from the service manual:
The ECT sensor is a two-wire Negative Thermal
Coefficient (NTC) sensor. Meaning, as engine coolant
temperature increases, resistance (voltage) in the
sensor decreases. As temperature decreases, resistance
(voltage) in the sensor increases.
OPERATION
At key-on, the Powertrain Control Module (PCM)
sends out a regulated 5 volt signal to the ECT sensor.
The PCM then monitors the signal as it passes
through the ECT sensor to the sensor ground (sensor
return).
When the engine is cold, the PCM will operate in
Open Loop cycle. It will demand slightly richer airfuel
mixtures and higher idle speeds. This is done
until normal operating temperatures are reached.
The PCM uses inputs from the ECT sensor for the
following calculations:
† for engine coolant temperature gauge operation
through CCD or PCI (J1850) communications
† Injector pulse-width
† Spark-advance curves
† ASD relay shut-down times
† Idle Air Control (IAC) motor key-on steps
† Pulse-width prime-shot during cranking
† O2 sensor closed loop times
† Purge solenoid on/off times
† EGR solenoid on/off times (if equipped)
† Leak Detection Pump operation (if equipped)
† Radiator fan relay on/off times (if equipped)
† Target idle

lilmatty · **Posted:** Mon May 22, 2006 11:58 pm

Replaced the temp sensor ($35 at NAPA) and the problem is solved. Thanks for all the help fellers.

Jeepjeepster · **Posted:** Tue May 23, 2006 6:49 am

That kinda had me worried. A friends cherokee was overheating one time and we could tell it was getting hot. turned out the radiator was bad so there was no way for use to tell it was hot, a thick iron block doesnt transfer heat to well.

Engine Temp Sensor and overheating

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