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Water temp sensor for 308

Discussion in 'Technical Q&A' started by Pizzaman Chris, Nov 25, 2010.

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  1. Pizzaman Chris

    Pizzaman Chris F1 Rookie

    Mar 13, 2005
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    #1 Pizzaman Chris, Nov 25, 2010
    Last edited by a moderator: Sep 7, 2017
    While im waiting for my motor to get assembled by David (fastradio) i need to do some homework on a few things. One in particular is the water temp sensor. I will be installing a Tec3 that i got from Nick to go with my EFI.

    What i read so far is that i need 2 water temp sensors. One for the Tec3 and one for the gauge.

    So far i located 3 water temp sensors. One at the water pump housing, one at the expansion tank and the 3rd one at the bottom corner of the radiator.

    The water housing one is called "Bimetal Thermostat"
    The expansion tank one is called "Bimetal Thermostat"
    The radiator tank one is called "Thermal Contact"

    The first 2 look the same. Short/little sensors with 2 prongs. I haven't looked at the radiator one yet.


    Do they all tie in together for the gauge?
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  2. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
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    #2 Steve Magnusson, Nov 25, 2010
    Last edited by a moderator: Sep 7, 2017
    None of those are related to the gauge in the dash.

    The water (pump) housing one is called "Bimetal Thermostat" = a thermoswitch to disable the cold start injector during warm restarts

    The expansion tank one is called "Bimetal Thermostat" = a thermoswitch that runs the cold-running stuff when cold (e.g., the electrovalve controlling the cold start air valve, the cold-running warning light in the dash, etc.)

    The radiator tank one is called "Thermal Contact" = a thermoswitch controlling the relays that run the radiator fans.

    To report the "true" engine coolant temperature to the Tec3 ECU, it should be mounted in the same place where the thermister is located that does run the dash gauge -- in the "Y" pipe where the hot coolant exits the cylinder heads (i.e., in item 27 here: http://www.ricambiamerica.com/parts_catalogs.php?M=FE&P=&V=diag&I=2270) in a similar manner as pad suggested in your other thread:
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  3. Pizzaman Chris

    Pizzaman Chris F1 Rookie

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    #3 Pizzaman Chris, Nov 25, 2010
    Last edited by a moderator: Sep 7, 2017
    Thanks for the reply Steve.

    Yes, I do have that sensor (104628) that you mentioned.

    The sensor for the Tec3 will be mounted on the water pump housing First picture, Nick recommended i put the Tec sensor at the water pump housing and the 104628 at the coolant manifold. Second picture.

    Where is the OEM water gauge sensor then? Did i miss it?
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  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
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    Jan 11, 2001
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    #4 Steve Magnusson, Nov 25, 2010
    Last edited: Nov 25, 2010
    No, you didn't miss it, but you are not understanding what pad did on his 308QV (which is slightly different than your 308i-2V). On his model, the 104628 thermister is mounted in a different location, and he added a boss for the extra thermister onto the top of the Y pipe:

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    The downside to using the water pump housing location is that, when the thermostat is open, the whole casting (being Aluminum with high thermal conductivity) will be cooled by the (colder) water entering from the radiator (so it will report a temperature lower than the Y pipe location which is thermally isolated from the water pump housing by the rubber hose coupling). I defer to Nick's experience if he know that that location will work OK, but on the later KE models (which have a separate coolant temp thermister for the injection ECU) both the injection ECU thermister and the gauge thermister are mounted in the Y pipe.
     
  5. Pizzaman Chris

    Pizzaman Chris F1 Rookie

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    #5 Pizzaman Chris, Nov 25, 2010
    I see what you're saying. When i was looking at the QV parts i didn't see a thermister at the water pump housing.

    Thanks Steve.
     
  6. DanielGA

    DanielGA Karting

    Mar 19, 2018
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    #6 DanielGA, Jul 31, 2019
    All, I am needing to decipher this issue and am hoping to revive this thread briefly. I have a 308-2V. On the engine block itself, near the oil filter, there is a temp sensor too I think. On the 308-2V, which one is for the gauge in the dash? I suppose I can use/replace the one in the "Y" for the EFI I am installing but I want to keep the dash gauge.
     

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