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Thermostat Issues

Discussion in 'The Garage' started by big_black_blazer, Apr 11, 2006.

  1. big_black_blazer

    big_black_blazer 1/2 ton status

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    i just got the tbi 355 in the 54 truck, and ran into something strange. the temp will not exceed 120 degrees. the fail proof thermostat is hung open, and i have only an electric fan, which runs all the time. i figured that cool temps was good since hot = bad, but i've been told that the computer doesn't operate properly until around 180 or 200 or so. any input?

    thanks

    evan
     
  2. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    If your T-stat is "hung open" it certainly isn't fail proof and is bad and needs to be changed. That truck also has a huge radiator so trying to get it hot enough could be a chore.
     
  3. big_black_blazer

    big_black_blazer 1/2 ton status

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    thanks for the reply. i was just wondering if the computer really didn't work until it reached a certain temp. don't make sense to me. and by the way, i like your truck, it looks just like my 90 k5
     
  4. 1979jimmy350

    1979jimmy350 1/2 ton status

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    with the engine runnign that cold the computer will throw more fuel in to try and get it to operating temp, which will kill fuel milage and might prevent some sensors from starting up which will make your engine run worse, defently change out the thermostat
     
  5. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Yes, the ECM needs to see a certain temp before it will allow closed loop operation. The way it works is like this, there is a coolant temp sensor that the ECM uses to read the engine temp, (different than temp sender for guage) your T-stat is what controls the engine temp so having a T-stat that is too cold will not allow the ECM temp sensor to reach the point in which it allows the ECM to go closed loop. I hope i've described this good enough for you. By the way, if the engine doesn't go to closed loop operation then all the other sensors aren't doing a thing and performance and mileage will suffer. Once the ECM goes into closed loop operation then all the other sensor outputs get relayed to the ECM so it can change fuel and timing accordingly.
     

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