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    Overheating in Extreme Cold Temperatures

    Good Day Gents,

    We've had some very cold days in Alaska and generally the M3 is fine in below freezing temps. One day we had -15°​f (-26°​c) in the morning and by afternoon, it had dropped to -20°​f (-28°​c). My car is parked in a heated garage over night, but sits outside at work. On both my commute into work and on the way home I experienced overheating, when normally it does not overheat. The cooling system is 100% factory and was 100% replaced from the fan at the front to the heater core over the last 4 years.

    On both occasions when the needle moved to the right dot I began monitoring it closely, and when moved passed the right dot, I parked the car at a the nearest gas station. I would shut the car down and go inside for 5 minutes, then come back out and within 10 seconds of starting the car again, the temperature was stable and no longer overheating. On both occasions I'd driven about 10 miles before it overheated, then drove another 10-15 miles home with no issues. Both times I popped the hood at the gas station and the upper radiator hose was very taught, like it was under pressure. There was no signs of coolant leaking from anywhere when doing a Quick Look in the frigid cold. In the morning, after the car sat all night I checked the coolant level and it was appropriate.

    Since that very cold day, the car has ran fine, never moving past centerline.

    At this point, my best guesses are that a line or a part of the system was frozen somewhere and when the car sat, enough heatsoak allowed the frozen bit to melt. My other thought is that the coolant is somehow boiling and the steam in the system is hitting the sensor causing a hot reading; once it has a few minutes to cool, it doesn't turn into steam again.

    Has anybody experienced similar problems or have any idea on how such cold temperatures triggers a hot coolant system?

    #2
    Either the temp sensor under the manifold is faulty or your thermostat got stuck in the close position. I would scan for codes and monitor the coolant temp on the OBC hidden menu.

    Comment


      #3
      What kind of coolant mix are you running? I wouldn't think you'd have issues freezing on the way in from the heated garage, but I wouldn't say it's impossible, the radiator is going to get to ambient temp pretty quickly if driving before the thermostat opens.

      You could test it out by running it in the heated garage with proper ventilation and see if the overheating still occurs, just be careful. If the thermostat is stuck closed then you should be able to tell by feeling how warm the radiator is, coolant won't be flowing through it so it'll stay cool.

      Comment


        #4
        Get a noncontact IR temp gun and point it at the thermostat housing to see what the actual temp of the cooling system is. Feeling both the radiator hoses would also give an indication if the system is icing up or the temp sensor is faulty.

        Comment


          #5
          Test the anti freeze mixture and get back to us

          Comment


            #6
            Originally posted by S14 View Post
            . I would shut the car down and go inside for 5 minutes, then come back out and within 10 seconds of starting the car again, the temperature was stable and no longer overheating
            You should have grasped the rad lower hose to check if it's cold or hot; I think it's cold as no coolant flowing through the rad, and the lower hose was softer than the upper hose (normally they should be at the same pressure).

            I think the T sensor and the gauge are correct. My guess the coolant in the radiator narrow channels were frozen, blocking the coolant flowing back to the opened Tstat.

            Comment


              #7
              The firm upper hose means the water pump pushing 100% of hot coolant from the head (subtract the amount flowing to the heater core if turned on). The pump expects to pull 100% coolant from the rad lower hose but zero coolant arrived due to blocked rad, and so the lower hose was collapsed at the moment. The only coolant flowing through the pump > block > head in this case was through the heater core if it’s turned on. If heater was off, I think the temperature gauge would have shot up very quickly as there were zero coolant flowing through the engine.

              Is it possible to have zero coolant flowing through the engine with a working pump? Yes if the Tstat is fully opened with blocked rad and the heater is off.

              Engine shut down for 5 minutes allowed the hot engine air to melt and unblock the rad narrow channels. The channels were frozen while the car was moving with a cold engine.

              Comment


                #8
                Originally posted by sapote View Post
                The firm upper hose means the water pump pushing 100% of hot coolant from the head (subtract the amount flowing to the heater core if turned on). The pump expects to pull 100% coolant from the rad lower hose but zero coolant arrived due to blocked rad, and so the lower hose was collapsed at the moment. The only coolant flowing through the pump > block > head in this case was through the heater core if it’s turned on. If heater was off, I think the temperature gauge would have shot up very quickly as there were zero coolant flowing through the engine.

                Is it possible to have zero coolant flowing through the engine with a working pump? Yes if the Tstat is fully opened with blocked rad and the heater is off.

                Engine shut down for 5 minutes allowed the hot engine air to melt and unblock the rad narrow channels. The channels were frozen while the car was moving with a cold engine.

                That's super interesting, makes total sense!

                We haven't had such low temps since creating this post and the car continues to run good. I have a jug of BMW coolant on order with FCP, currently there is a 50/50 mix in the system and it was last flushed in 2023. I do wonder if blocking off the kidney grill similar to how semi trucks block off their radiator might help if we see negative temps again.

                Comment


                  #9
                  Originally posted by S14 View Post

                  That's super interesting, makes total sense!

                  We haven't had such low temps since creating this post and the car continues to run good. I have a jug of BMW coolant on order with FCP, currently there is a 50/50 mix in the system and it was last flushed in 2023. I do wonder if blocking off the kidney grill similar to how semi trucks block off their radiator might help if we see negative temps again.
                  Too bad that the AC is disabled at very ambient T; if it can run then the consensor should generate the heat to keep the rad from frozen.

                  Turn the cabin heat to max with max fan speed to see if this helps preventing engine overheat while the hot engine radiated heat helps melting the rad.

                  Blocking the grill/rad should help.

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