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radiator sensor???

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  • radiator sensor???

    Can anyone tell me what the two prong sensor is for at the bottom of the 88 radiators? I bought a new radiator and it didn't come with the hole for it???

  • #2
    Im wondering too. My rad on my efi car doesn't have it but i pulled a rad out of a carbed car and it has it...

    Sent from my iPhone using Tapatalk


    • #3
      89 EVTM says C158 is the radiator temperature switch
      It serves as an input to the 1L circuit in the EFI ECA.

      In the non-EFI ECA it is in connector C109. Again input to 1L circuit.

      If the car stalls then the Q1 pinpoint test will tell if the radiator temperature switch is malfunctioning or not.

      The ECA uses the input to calculate other parameters. The rad temp switch has high voltage (10-12V) when the coolant is below 17C during cold starts at fast idle and cold driveaway at part throttle. The rad temp switch has low voltage (0-1.5V) when the coolant is above 17C during warm driveaway at part tjrottle, hot cruise.
      Last edited by bravekozak; 09-25-2015, 10:36 PM.


      • #4
        + deceleration at closed throttle and hot curb idle.

        Outputs affected:
        air/fuel mixture, idle speed control, canister purge control, ignition timing.
        Last edited by bravekozak; 09-25-2015, 10:48 PM.


        • #5
          Hmmm... interesting. So I wonder if on the efi cars they found a different way of doing it? (Seeing how it doesn't have the sensor)
          I'll have to try running it with it unhooked for awhile and see if I notice any problems. The new radiator doesn't have the hole, so I would have to make an in line connection to hook it up again. Thanks for the info.


          • #6
            Thanks Brave for the explanation. I THINK this is the first time I saw anything posted as to what the switch is SUPPOSE to do.

            I bought a new radiator without the switch hole for my '89 EFI/auto a while back and simply left it unplugged. Didn't seem to make any difference. No stalling or quitting.

            Then again, the switch could have been bad to begin with.

            Thanks again.


            • #7
              Someone wrote here that the computer on the carburetted models does not adjust timing.
              Original owner of silver grey carburetted 1989 Festiva. 105k km as of June 2006. 140k km as of June 2021.


              • #8
                I'm reviving this old thread because I just bought a new radiator for Trixie (my 1989 EFI automatic) because the old one started leaking around the upper plastic to metal seal. When I took off the top hose I noticed that that round plastic snout that the hose connects to was cracked also. Long story short.. when I got the new radiator everything is good except that the hole where the radiator temperature switch screws in is too small. The selection for Festiva replacement radiators seems to have become very limited. Anyone else finding this a problem? I bought mine from and have notified them of the problem. Haven't heard back but I don't really expect any solution from them. Anyone else had this problem?


                • #9
                  1990new.... I had the same issue back in 2015.. I couldn't find ANY radiators with the hole for the sensor.


                  • #10
                    I read your post about the issue.. Is you Festiva still running OK without the radiator temperature switch connected?


                    • #11
                      It ran fine for a lot of years without it connected.... It has since been retired due to rust taking over to the point of not really being safe to drive any more.... I still own it, and it's now been put into the 'parts donor/possible future project' area of my property.


                      • #12
                        Sorry about the rust eating your cars... Lucky for me I live where we consider ourselves fortunate if we get snow every 10 years; so no rust problems.. but the sun does eat our plastic and fade our paint. I did some testing with ice water and warm water on the switch and it appears that it offers no resistance across the pins until the temperature drops below about 62 degrees and the resistance goes up as the water gets colder. Leaving the connector off would be like never sending a signal to the ECM that the temperature of the water was lower than 62. If your Festiva started and ran OK in the winter where you live, I should definitely have no problem leaving it unhooked here...