News

Warm up high rpm's doesn't turn off

Discussion in 'Technical Q&A' started by thedunk, Mar 4, 2021.

  1. thedunk

    thedunk Rookie

    May 6, 2015
    17
    Claremont, CA
    Full Name:
    Kent Miller
    I just replaced the expansion tank on my 308. I pumped the coolant out of the tank before I started and pumped it back in after in had completed the install. I put all of the sensors and hoses back exactly as they were originally. The little hoses on the run-up temperature sensor don't fit real tight but they fit about as tight as they did before the tank exchange. I am not sure what the other temperature sensor is for but the electrical connections seen secure. My guess is air in the cooling system line but I am not sure. Has anyone else made this exchange and had this problem. What should I do next?
     
  2. To remove this ad click here.

  3. flash32

    flash32 Formula 3

    Aug 22, 2008
    2,477
    Central NJ
    Full Name:
    Dominick
    I believe .. if memory serves me correctly .. early 308's have a temp sensor on the bottom of coolant tank .. check that out
     
    WaltP likes this.
  4. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    20,313
    Texas
    Full Name:
    Steve Magnusson
    Please give year/version 308. If you have the yellow "cold running" warning light in the dash, are you saying that this light doesn't go out after warm-up is completed?
     
  5. thedunk

    thedunk Rookie

    May 6, 2015
    17
    Claremont, CA
    Full Name:
    Kent Miller
    This is a 1981 308 GTSi. There are two thermal sensors that screw into the bottom of the expansion tank. One has two electrical connections and the other has two vacuum lines. Another owner told me that startup high rpm's is not controlled by anything connected to the expansion tank. Is this true? If it is why does my high rpm startup no longer turn off after replacing the tank? Maybe my '81 is different than my friends QV?
     
  6. thedunk

    thedunk Rookie

    May 6, 2015
    17
    Claremont, CA
    Full Name:
    Kent Miller
    The yellow light never turns off because the startup high RPM never turns off after the usual few minutes.
     
  7. To remove this ad click here.

  8. Steve Magnusson

    Steve Magnusson Two Time F1 World Champ
    Lifetime Rossa

    Jan 11, 2001
    20,313
    Texas
    Full Name:
    Steve Magnusson
    #6 Steve Magnusson, Mar 5, 2021
    Last edited: Mar 5, 2021
    The way your '81 US 308 works is:

    When the coolant is cold, the electrical thermoswitch on the coolant expansion tank is open = this turns on the yellow light and operates the cold start air valve to raise the engine RPM.

    When the coolant is warm, the electrical thermoswitch on the coolant expansion tank closes = this turn off the yellow light and deactivates the cold start air valve (lowering the engine RPM).

    As a first test, just use something metal to connect the two wires of the electrical thermoswitch on the coolant expansion tank together during warm idle (simulating a warm, closed electrical thermoswitch). If the idle RPM drops and the yellow warning light goes out = you probably have a bad electrical thermoswitch 115477 (or your coolant level is so low there is no coolant in the expansion tank).

    The thermo-pneumatic sensor with the small vacuum hoses on the coolant expansion tank is for the EGR system and has nothing to do with the idle RPM speed.

    PS 1983 US 308QV are similar to your 1981 US 308i with regard to how the cold fast idle works. 1984-85 US 308QV are quite different from your 1981 US 308i with regard to how cold fast idle works.
     
    f355spider likes this.

Share This Page