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Thread: Bad Thermostat?

  1. #1
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    Bad Thermostat?

    So I was driving home yesterday from my grandparents house, about an hour drive, and in the last mile or so, my heater stopped blowing hot air and when I parked, there was steam spewing from the coolant tanks overflow tube.

    Is this the sign of a bad Thermostat? I've already replaced the otterstat a few months ago, so I know the fans are running when they should, but because of where the otterstat is located in the system, if the thermostat is frozen closed, hot water would never pass by the otterstat to activate it, correct?

    Thanks,
    Brandon

  2. #2
    Senior Member DMC5180's Avatar
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    Bad Thermostat?

    Was your last mile of driving at slow in town stop n go?


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    VIN 5180, Frame 3652, STAGE I, DM-eng Solid State Solutions (RPM Rly, Dm.Lt.Mod., Fan Fail Mod. , FAN Rly, HS.Rly) , HID sealed beam style headlights, SPAX user since 2009, Eibach springs, Mid-State Club Adj. Rear LCA's, DPNW poly-sway bar kit, DMCEU LCA Stabilizer link kit, DMCMW Illuminated door sills, Aussie Illuminated SS Shifter plate, GENUINE MOMO EVO Steering wheel, DELOREANA Extended View Side Mirrors w/ Heaters, DELOREANA LED Door Lights.

  3. #3
    Senior Member DMC5180's Avatar
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    Quote Originally Posted by DMC5180 View Post
    Was your last mile of driving at slow in town stop n go?


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    Did you observe a higher than normal water temp?


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    DENNIS

    VIN 5180, Frame 3652, STAGE I, DM-eng Solid State Solutions (RPM Rly, Dm.Lt.Mod., Fan Fail Mod. , FAN Rly, HS.Rly) , HID sealed beam style headlights, SPAX user since 2009, Eibach springs, Mid-State Club Adj. Rear LCA's, DPNW poly-sway bar kit, DMCEU LCA Stabilizer link kit, DMCMW Illuminated door sills, Aussie Illuminated SS Shifter plate, GENUINE MOMO EVO Steering wheel, DELOREANA Extended View Side Mirrors w/ Heaters, DELOREANA LED Door Lights.

  4. #4
    Junior Member
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    Last mile was still on the freeway. Unfortunately, I'm not sure if the temperature because the gauge stopped working 2 weeks ago.

  5. #5
    TGTF (Too Greek to Function) AugustneverEnds's Avatar
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    Notice any coolant drips anywhere? You may have a small leak the allowed enough air in to airlock the cooling system. Having a pressure tester is very useful on occasions like these, Autozone will loan you one if you don't have access to one
    Nick A.
    Νικος Αυγουστινατου

    1988 BMW 325iS
    1982 DeLorean DMC-12

  6. #6
    Senior Member Rich's Avatar
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    Quote Originally Posted by villevol666 View Post
    So I was driving home yesterday from my grandparents house, about an hour drive, and in the last mile or so, my heater stopped blowing hot air and when I parked, there was steam spewing from the coolant tanks overflow tube.

    Is this the sign of a bad Thermostat? I've already replaced the otterstat a few months ago, so I know the fans are running when they should, but because of where the otterstat is located in the system, if the thermostat is frozen closed, hot water would never pass by the otterstat to activate it, correct?

    Thanks,
    Brandon
    Maybe, but more likely this is a sign of either low coolant level (leak), a poorly-bled cooling system or the rad fans failing. The first two issues would be a problem at any speed, the last one would be a problem around town except in hot weather - which we do not have in SF this weekend. Sounds like the heater stopped working after the freeway segment of your drive.

    Refill the system, making sure it is bled correctly. Then make sure the otterstat is behaving correctly (harder to do if the temp gauge isn't working, though) during some around-town testing or idling for 10-15min. Also make sure your otterstat pipe tee is facing downward (otterstat needs to be under the pipe, not above it).

    Have you noticed any signs of coolant leakage recently? Nick's pressure test is a good idea.
    Last edited by Rich; 03-11-2018 at 04:41 PM.
    March '81, 5-speed, black interior

  7. #7
    Senior Member DMC5180's Avatar
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    Quote Originally Posted by villevol666 View Post
    Last mile was still on the freeway. Unfortunately, I'm not sure if the temperature because the gauge stopped working 2 weeks ago.
    Hate to say it, but there is a lesson to be learned here. You must have some kind of temp indication whether a gauge or warning light. Deloreans donít have warning lights, so you must have a functional gauge.

    My guess is your cooling fans are not functioning like you think.

    Unplug the wires at the otterstat add jumper them to gather, turn the key to run, they should turn ON. If they donít youíll need to troubleshoot.




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    DENNIS

    VIN 5180, Frame 3652, STAGE I, DM-eng Solid State Solutions (RPM Rly, Dm.Lt.Mod., Fan Fail Mod. , FAN Rly, HS.Rly) , HID sealed beam style headlights, SPAX user since 2009, Eibach springs, Mid-State Club Adj. Rear LCA's, DPNW poly-sway bar kit, DMCEU LCA Stabilizer link kit, DMCMW Illuminated door sills, Aussie Illuminated SS Shifter plate, GENUINE MOMO EVO Steering wheel, DELOREANA Extended View Side Mirrors w/ Heaters, DELOREANA LED Door Lights.

  8. #8
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    Fans are new. Replaced 5 months ago.

  9. #9
    Senior Member DMC5180's Avatar
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    Quote Originally Posted by villevol666 View Post
    Fans are new. Replaced 5 months ago.
    Doesnít mean they are turning ON when needed though. What setup do you have in place of the blue fan fail module?


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    DENNIS

    VIN 5180, Frame 3652, STAGE I, DM-eng Solid State Solutions (RPM Rly, Dm.Lt.Mod., Fan Fail Mod. , FAN Rly, HS.Rly) , HID sealed beam style headlights, SPAX user since 2009, Eibach springs, Mid-State Club Adj. Rear LCA's, DPNW poly-sway bar kit, DMCEU LCA Stabilizer link kit, DMCMW Illuminated door sills, Aussie Illuminated SS Shifter plate, GENUINE MOMO EVO Steering wheel, DELOREANA Extended View Side Mirrors w/ Heaters, DELOREANA LED Door Lights.

  10. #10
    Junior Member
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    Not sure I have anything in place of the blue fail module. Having said that, if the fans work, the otterstat works, the relay works and the fans come on when I jump the otterstat, how could it be fan related?

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