rocket22

I got this car last year, no temp reading was occuring and radiator was leaking.

Replaced Radiator and bled system correctly (twice) -filled from upper point on this DOHC and still getting no reading. New Temp sensor was put in.

Here are the questions:

How do I test the
1) Sensor to make sure the car is in range
2) Gauge: how do I confirm the gauge is working correctly - if not how do I replace?
3) Fan: I am assuming the fan turns on by computer, what is the turn on temp and how can I test?

Thanks for your help!

Stevo86

You're going to need to back probe (stick a paper clip or something in the back of the connector) the signal wire as the engine heats up to measure the voltage it is putting out. It should increase steadily as the engine warms up.

rocket22

how can this be tested with an ohmeter and what readings should I get? Also, how can i test the dash gauge from the connector?

Stevo86

You can't test it with an ohm meter unless you just want to know it isn't literally broken inside. The resistance changes with temp. It's only a two pin sensor so just ohm across the pins.

However like I said you need to measure it's voltage output. One pin should be 5 volt reference and one signal.

blu30val

Here's some info for you. I'm not too familiar with 4.6dohc but I should be able to help. Keep in mind a stuck open thermostat will cause low readings.

rocket22

It has been my experience that a stuck open tstat will slow down the rate at which the coolant heats up, but will still get to op. temp. Since I have no history of repairs on this car, outside of the radiator and sending temp unit, I will replace the themostat if it is an easy repair. I am more familiar with 5.0, LT1 and M54 engines so not sure how difficult replacing the tstat is on this car.

petrock

Yes you can test this sensor with an ohmmeter since this sensor is a thermistor (resistance (ohms) increases or decreases based on the temperature of the sensor). If you know the ohm range of the sensor then you can test the sensor with an ohmmeter. However, ohm ranges vary from manufacturer to manufacturer and from sensor to sensor. And whats worse is the ohm reading will vary based on the temperature of the sensor so you’ll get different ohm reading after holding the sensor in your hand a few minutes. It is best to measure the voltage of a thermistor with a voltmeter. A two wire temp sensor works by taking 5 volts in one wire and letting a signal voltage between 0 & 5 volts out the other wire. This signal voltage represent the temperature of the motor. I don’t know if 0 volts represents cold or hot, but it really doesn’t matter with the low temp code your getting.

Either way, warm the car up so the motor is noticeably warm to the touch. Then back probe each wire one at a time. The voltage on one wire should be 5 volts. The other wire should be somewhere between 0 & 5 volts. If the sensor is working properly, and the car is fully warmed up, you’ll get a voltage somewhere in the middle.


Yes, this is true if the car is sitting still. The cooling fan will kick in to keep the engine temps in check. But if you drive the car the air flowing through the radiator will cool the coolant down lower then normal temps.