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I have a 2006 Honda fit 1.3L IDSI and Im having a cooling system problem. Engine Coolant Temp gauge always at cold. can u guys help me narrow down the cause of this? enter image description here I recorded some data with my phone from the last time I drove the car.

Y=Engine Coolant temp in °F
X=Time

Could this be a bad thermostat?

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  • please give a bit more information what have you tried to do to confirm the temparature reading,does your heater blow hot air?
    – trond hansen
    Commented Mar 19, 2020 at 6:15

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This is most definitely a sensor issue. I state that because of the drop in the graph. It looks as though the engine comes up to temperature, then the sensor stops putting out the correct temp reading. Most temperature sensors work on a resistance basis. As the temperature it is reading goes up, the resistance gets higher, and the computer computes this resistance as a temperature. If the sensor were shorting, it would either peg it to maximum temperature or drop like a rock to minimum (depending on how it functions). Since it did neither of these, it wouldn't be a wiring short.

You can test your temp sender by pulling it out, then testing the resistance. Put a multimeter on the leads, then put it into a pot of boiling water. If the resistance suddenly goes away after period of time, then you know for sure you have your culprit. Just be sure you are messing with the right sensor. Also, you'll want to ensure you plug the hole while you have the sensor out, or you'll drain all of your coolant.

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  • Thanks for the feedback. Ill see what I can do. I dont have a multimeter as of the moment, but ill buy it as soon as i can and proceed with your suggestion
    – john natalis
    Commented Mar 19, 2020 at 22:43
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Is the upper radiator hose hot to touch after you have been driving,if yes the reading is clearly wrong(60-80F is less than hand warm).

If the hose is cold your thermostat might be stuck open,so the reading might be correct.

You can test the temparature by turning on the heater while driving.

does it blow hot air if yes the temparature reading must be wrong and if it blows cold air your temparature reading is probably correct.

The first part of your graph show the ideal temparature of the coolant,so the sudden drop in the graph makes me think the temparature sensor is failing(normal coolant temparature is 190-200 F).

Your temparature sensor is most likely failing or have a bad connection,do you have any error codes stored if yes what codes?

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  • Im using a cheap bluetooth obd2 scanner so im a bit skeptical about its ability to scan codes but to answer your question, there were no codes when i scanned it
    – john natalis
    Commented Mar 19, 2020 at 22:40

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