Thermostat
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Thread: Thermostat

  1. #1
    Fellow Frogger! Andreas's Avatar
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    Thermostat

    When i got my car back after the mapping of the ecu a few things weren't right with the car.
    The cooling fans are constantly on high speed and yesterday i noticed a few drops of coolant below the thermostat housing.
    The car takes a long while to reach temp and the people who mapped the ecu said it took a while to reach temp even after they removed the fuse for the fans.
    Now would a thermostat that remained open cause the fans to stay on?
    I dont have much experience with working on engines so alot of this is new to me.
    How do i test it without removing the thermostat?

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  2. #2
    1000+ Posts PeterT's Avatar
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    Sounds like the coolant temp sensor under the thermostat housing (not the other one on the end of the block) has come off, or has become corroded by the green juice. Open circuit or high resistance will cause the fans to go to high speed as a safety precaution. One of the lights on temp guage is probably on too. The cooling is controlled by another smaller ECU under the steering column.

    '92 205 Mi16
    '90 Mi16x4

  3. #3
    Fellow Frogger! Andreas's Avatar
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    thanks for that, i'll have a look tomorrow
    cant remember a temp gauge light being on though.
    i dont use the motronic ecu anymore, it's now a motec, could this affect the other ecu you referred to.

  4. #4
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    Andreas,

    You can check if the thermostat is stuck open
    by simply squeazing the top hose that runs from the thermo to the radiator
    You can feel the water running through it when it shouldn't be untill engine is up to temp
    What u mentioned about the fans being on if the thermostat is open would be reverse
    They would come on later as cold coolant would be circulating the radiator
    The coolant leaking would simply be coming from the hose that u mentioned they will need retightening as they expand and shrink
    They always need tightening after hoses have been removed due to engine work they need time to settle in just tighten them a little

    Murat

  5. #5
    Fellow Frogger! Andreas's Avatar
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    surprise, surprise!
    the sensor under the housing wasn't even plugged in.
    fans operate as they should now!

    Andreas

    p.s met a guy at the auto elec's this morning (didnt go because of fans!) and he used to work as a pug mechanic in the Middle East.
    He said they recalled the mi16 motors because they kept running after switching off due to the hot climate, and they were replaced with turbo diesel motors.
    He's also done a few mi16 conversions
    hmmmm

  6. #6
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    I think I have the same problem with my 306 - always seems to be running cold. Had a look around the thermostat housing area and could see an unconnected wire just dangling. Could not get my hand to it though (area just too crowded) and could not see where it is supposed to connect to. What should I be looking for and do I need to disconnect a number of hoses etc. to get to it?

  7. #7
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    my 306xsi is always running cold. and has done so for the last few months. i went and checked the radiator and went in behind the heaters today to see if the dial might have broken, but now the air con is only blowing at a minimal temperature. how anoying. any ideas about how to get the heat back on?

  8. #8
    Moderator Alan S's Avatar
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    My BX 16V has gone the other way.
    It used to run fairly cool like 70 to 85 degrees when I was running into town or going to school. I have just done a swag of maintenance jobs on it that have included cambelt, pump, new thermostat, new radiator cap, new plugs, new thermal switch for the fan (which works at a lower cut-in temp) amongst others.
    NOW when I head for town, in no time it hits 90 deg, but whereas before, as soon as I started to get balked with traffic & had to stop at lights or just drive slowly, instead of jumping to 95 - 105 as it used to, it now goes to about 92 at which point, the fans cut in and it maintains this temperature around 90 degrees. The thermostat I got looked a bit smaller in some respects to the one that I took out and didn't have any rubber gaskets with it hence I had to use the ones off the old one.
    Does anyone elses car (Mi16) perform lioke this? I'm presuming that mine is working correctly but I don't have other cars to do comparisons with.
    We were recently talking on a BX 16V specific site about this heat with the 16 valvers and it was noted that over there, the cars that take quite a while to warm up & quite often run too cold, all had steel sumps whereas the ones with alloy sumps (like mine) tended to go the opposite. They were of the opinion that the alloy sumps tend to hold the heat better than the steel ones. Do any of you guys have the steel sumps ot were these just something they got overseas?

    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  9. #9
    1000+ Posts PeterT's Avatar
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    My '89 Mi16 behaves pretty much like what you've described after doing the thermostat job. It also has the alloy sump, even though it was a private import, though I doubt that it's a factor. A friend's Mi16 (also private import with alloy sump), behaves as per your previous condition. Where does that lead us? I'd say your thermostat was faulty (and my friend's), and that not all European cars had steel sumps.

    '92 205 Mi16
    '90 Mi16x4

  10. #10
    Moderator Alan S's Avatar
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    PeterT:
    My '89 Mi16 behaves pretty much like what you've described after doing the thermostat job. It also has the alloy sump, even though it was a private import, though I doubt that it's a factor. A friend's Mi16 (also private import with alloy sump), behaves as per your previous condition. Where does that lead us? I'd say your thermostat was faulty (and my friend's), and that not all European cars had steel sumps.
    No no Peter, I didn't say "all" European cars had steel sumps; quite a few of theirs have alloy also but they thought that perhaps the common denominator that they could see was that the cars with alloy sumps over there also had air/con, then one guy came up with the fact that his had both air/con and the steel sump and he knew that the motor had been transplanted so they were still sticking with that theory.
    It was very strange though that every alloy sumped car tended to get hot fairly quickly in traffic whilst the steels were all complaining of cool running. May have been coincidence and was just mentioned as a point of curiosity.

    Alan S
    If it ain't broke, use a 12" shifter.....that usually does the trick!!

  11. #11
    pur-john, not pew-john! peujohn's Avatar
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    After a new radiator and thermostat in my '90 Mi16 it runs from 70 to 85 when on the move, depending on how hot the day is, and doesn't get above about 90 in traffic. I've been told that on Mi16s the fan cuts in at 88 degrees, once it cuts in on my car, it keeps it from getting much hotter no matter what the conditions are, I think it cools down to about 80 before it cuts out again.

    Seems to me that's how it should be, with a new radiator and thermostat...?

    John
    John W

    1979 Peugeot 504 GTI 2.2 litre 5 speed - 72 kW at the wheels

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    Previous: 2005 407 HDI manual sedan, 1980 504 GL, 1990 405 Mi16, 1977 504 GL Special, 1984 505 SRD Turbo



  12. #12
    1000+ Posts PeterT's Avatar
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    From memory, the fans on an Mi16 will go to slow speed at 92 deg., which should return the temp to 85 deg. before switching off. The fans also turn onto slow if the A/C compressor is on. If the temp keeps rising, the fans will go to high speed at 97 deg. If that doesn't cool things........meltdown! You can check the high speed setting by disconnecting the sensor below the thermostat housing. The fans should go immediately to high speed. It's a good fail safe method of ensuring the motor will be cooled if the sensor fails in anyway.

    '92 205 Mi16
    '90 Mi16x4

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