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test water gauge or connection?

Discussion in '308/328' started by Doug, May 25, 2009.

  1. Doug

    Doug Formula 3

    Nov 13, 2003
    1,467
    Louisville KY
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    Doug
    I have everything in my '77 308 sorted except the water temp gauge doesn't work. Is there a way to test if it is the gauge or the sensor? There is a disconnect in the engine bay and I was wondering if there is something that can be plugged into the gauge side to test or a way to test coming directly off the sensor.
     
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  3. PT 328

    PT 328 F1 Rookie
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    May 1, 2005
    3,452
    Have you tapped on the gauge? Sometimes they get stuck.
     
  4. irondogmike

    irondogmike Formula 3

    Sep 8, 2006
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    Michael Tucker
    #3 irondogmike, May 25, 2009
    Last edited: May 25, 2009
    I took the gauge out and rotated it then back to level,if the needke moves back to zero fast its no good,goes back slowwwww,then its good,that work when I tested mine,and I put a new one in and vala no problems,you see I found out that mine had a poor spring inside which made the needle to go back fast,
     
  5. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    The first thing to do is remove the wire connector for the water temperature sensor on the engine and touch it to ground (i.e., the engine block or cylinder heads) -- two results are possible:

    1. If the gauge needle (with the key "on") goes to maximum, all is OK with the gauge/power, and the trouble is probably the sensor. These sensors are designed to have a high resitance when cold and a low resistance when hot (so touching the wire directly to ground simulates a very hot sensor with 0 Ohms resistance).

    2. If the gauge needle (with the key "on") doesn't move -- either a bad gauge, or an electrical power problem upstream of the gauge, or a wiring problem between the engine and the gauge.
     
  6. irondogmike

    irondogmike Formula 3

    Sep 8, 2006
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    Michael Tucker
    I did not know that,thats alot better than taking the guage out
     
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  8. Doug

    Doug Formula 3

    Nov 13, 2003
    1,467
    Louisville KY
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    Doug
    Thanks Steve, that's what I needed. The tap the gauge didn't work so I was hoping to find which direction to take for disassembly.

    Just to confirm: grounding the wire to the gauge with the ignition on should result in a max temp reading? If so, then the sensor needs to be replaced? Is there a way to test the sensor? Maybe it is a connection to it?
     
  9. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
    20,293
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    Steve Magnusson
    #7 Steve Magnusson, May 25, 2009
    Last edited: May 25, 2009
    Yes

    If the gauge works OK during the test, the next thing to do would be to measure the resistance from the male tab on the sensor to ground when both cold and hot (and, of course clean-up, tighten-up, and/or "wipe" -- i.e., unplug/replug, the connection if it obviously seems poor). IIRC, the resistance should be something like ~500 Ohms when cold and maybe ~100 Ohms at a normal warm temperature -- but don't quote me on those resistance numbers (and if someone has more recent data/information for these thermistors please post). If the male sensor tab -to- ground measures infinites ohms, whether cold or hot, then that would be a clear sign that the sensor should be replaced.
     

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