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Thread: Coolant flow

  1. #1
    Senior Member Bitsyncmaster's Avatar
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    Coolant flow

    I was just thinking about the otterstat and was wondering which way coolant flows? Is the otterstat in the return (flow from the radiator) or the hotter flow from the engine.
    Dave M vin 03572
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  2. #2
    Senior Member Chris 16409's Avatar
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    Here is my reasoning:

    Hot coolant is piped along the passenger side to the radiator. The coolant temp at the radiator decreases and is sent back to the engine along the driver side. This coolant passes by the otterstat. If the radiator is doing it's job and the coolant temp is low enough, the otterstat is not tripped and the fans won't go on. If however the returning coolant has not been sufficiently cooled by the radiator, the otterstat will be tripped and the cooling fans will turn on. Now the fans will aid in reducing coolant temperature.
    Chris Miles

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    Senior Member Christian Dietrich's Avatar
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    Hotter flow from the engine. Engine temps warms up, opens the termostat and on its way down the pipe, trips the otterstat to turn on the fans as it hits the radiator. I did this with a thermol heat gun.

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  4. #4
    Matt Drive Stainless's Avatar
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    The coolant exits the engine and travels down the driver-side of the car.
    And here is a pic of the water pump area:CoolingSystem.jpg
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  5. #5
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by Drive Stainless View Post
    The coolant exits the engine and travels down the driver-side of the car.
    And here is a pic of the water pump area:CoolingSystem.jpg
    That what I assumed. Yes the drivers side comes from the thermostat so I think you drawing shows that.

    I would assume it would be better to have the otterstat in the return line as Chris pointed out it would not need to run the fans as much.
    Dave M vin 03572
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  6. #6
    Formally hmm252000
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    It works like this. Once the engine coolant gets to 87C, the thermostat opens and hot coolant leaves the engine on the driver's side. The otterstat switch does not close at this time and the fans stay off. Assuming the car is in motion, the coolant is cooled down a bit and the engine temp drops until the thermostat closes. Now if the car isn't moving, the temp will continue to increase even with the thermostat open. Once the coolant reaches 97C, the otterstat switch closes and the cooling fans come on. They then cycle as the switch only closes once the temp drops below 92C. If the car starts moving again, the coolant temp will drop past 92C and the fans stay off and the thermostat will eventually close once it reaches 87C.

    As I learned, a mechanic replaced my thermostat with one that opened around 92C. The cooling seems normal until the coolant temp reaches 97C. The fans kick on, but because the thermostat closes with 92+C coolant in the pipe at the otterstat switch, the fans never turn off again! So if you have fans that never turn off after the engine sits in traffic, then you have the wrong thermostat.

  7. #7
    LS1 DMC Nicholas R's Avatar
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    Also for what it's worth, you pretty much always have hot coolant enter at the top of a radiator and exit at the bottom. If you know which pipe goes to the top of the radiator, you can safely assume that's the one that delivers hot coolant from the engine. In the case of the DeLorean, the pipes on the driver side of the car are delivering coolant from the engine to the radiator.

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    Logically you would want the "O" switch in the rad near the exit (lower passenger side). That way it senses what is coming out of the rad and if it is too hot it starts the fans. Conversely if it is cool enough (you are moving and air is being rammed through the rad without the need to run the fans) the "O" switch doesn't need to turn on the fans.
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  9. #9
    Senior Member Bitsyncmaster's Avatar
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    I think were pretty sure the return line is the passenger side but I may just temperature check each side to verify.

    So if we want the fans to turn on at the same time but mount the otterstat on the return side, I'm guessing you would need a lower temp otterstat.

    I still think the design would be better with the otterstat in the return line since the amount of BTU cooling changes via car speed and ambient temperature. We do want to maintain engine temp as best as possible for best efficiency.

    Yes I was thinking about an electronic "otterstat" switch design. Of course it would be adjustable so you could set the fan on and off temps. Was also thinking about adding an audio alarm in case the temp goes above another set temp.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  10. #10
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    Dave, the Lotus Temp. sensor is located in the top of the thermostat housing. Easy to get to and test.

    Steve

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