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Thread: BMW E46 - Strange overheating problem

  1. #1
    Join Date
    Oct 2018
    Location
    Bournemouth, Dorset, UK
    Posts
    3
    My Cars
    BMW E46 325CI

    Exclamation BMW E46 - Strange overheating problem

    Hello there,

    Thought I would give everyone a shout here as I'm told you guys will know what to do!

    On my E46 325 the coolant temperature dial will sometimes go into the red for a while and then straight back down to the middle, it's actually very occasional and usually sticks steady to the 12 o'clock as it should. I've replaced the thermostat about 2 years ago with a part from Ebay so I don't think it could be that however I guess it's a possibility (I wouldn't expect it to fail this early). I've connected the fan to an independent temperature sensor on the top hose and when the temp goes into the red the fan doesn't come on. I know the fan is working as it comes on in heavy traffic as expected. So I've got the following questions:

    * Could it be that the car is not overheating and the coolant temperature sensor at the back on the cylinder head is not giving a correct reading and therefore needs replacing?
    * Is the reason that the fan is not coming on when it goes into red is because it gets the temp reading from being connected to the top hose which if the T stat is stuck closed will not be getting the hot water through to trigger it?
    *Can the T stat fail in a closed position and not go through the radiator?

    Thank you so much in advance, any suggestions would be helpful at this point!!

  2. #2
    Join Date
    Apr 2015
    Location
    Netherlands
    Posts
    164
    My Cars
    2000 E46 328i
    Sticky thermostat is definitely possible, especially if your T-stat is not an OEM part.
    If your thermostat is closed you have little water circulation so your fan will also not come on.

    I'd say replace the T-stat with an OEM part.

  3. #3
    Join Date
    Jul 2011
    Location
    Arlington, VA
    Posts
    9,933
    My Cars
    2018 BMW M240i
    Stop driving the car or else you’ll need a replacement engine. The M54 engine is made of an aluminum alloy that does not tolerate overheating. The cooling system is the Achilles heel of the E46. I concur with the previous poster: get rid of that aftermarket thermostat! Aftermarket cooling system parts are strictly verboten!! Buy a Whaler thermostat from FCPEuro. The company is in Connecticut so shipping will be quick. Properly bleed the cooling system using the process described at E46Fanatics.

  4. #4
    Join Date
    Oct 2018
    Location
    Bournemouth, Dorset, UK
    Posts
    3
    My Cars
    BMW E46 325CI
    Thank you both for your advice, I've ordered a the Walher thermostat this evening and I'm going to fit tomorrow! I just have to hope I've not damaged it too much by leaving it this long.. Thanks again!

  5. #5
    Join Date
    Jul 2011
    Location
    Arlington, VA
    Posts
    9,933
    My Cars
    2018 BMW M240i
    Good. Report back the results. Make sure you bleed the cooling system in accordance with the process listed at E46Fanatics.

  6. #6
    Join Date
    Oct 2018
    Location
    Bournemouth, Dorset, UK
    Posts
    3
    My Cars
    BMW E46 325CI
    Quote Originally Posted by MarcoZandrini View Post
    Good. Report back the results. Make sure you bleed the cooling system in accordance with the process listed at E46Fanatics.
    So results are pretty much perfect with the temperature needle going to 12'oclock and staying there with doing a variety of journeys whereas before I would encounter problems. Only managed to catch it out once when I was going 95+ on the motorway and then lifted off the gas and coasted (I was trying to catch it out) and the temperature fell briefly before returning to the right position. From revving high to insane amounts of air cooling I would expect it to take a second to catch up so not too worried by this.

    Car is showing low coolant which I'm thinking is lack of bleeding, will open the bleed valve again when hot to let some air out but not too worried as I drove it for almost 2 years like this. Water levels are at the top as well. Thank you again for pushing me into changing this, only took me an hour to change and was incredibly simple!

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