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545i “overheating” glitch (a real mystery)

563 Views 5 Replies 4 Participants Last post by  Burning2nd
Hi y’all! I’m about at my wits end with my car currently! I have a 2004 545i with just under 60k on the odometer. I’ve been driving it for a year and put about 15 thousand miles on it and when I first got it I had an issue where an “over heated engine” warning would appear on the idrive then disappear. I went ahead and replaced the water pump (with an OEM), all the temp sensors, and did a coolant flush and that was that. I hadn’t seen the warning for about 6 months until yesterday when it appeared with the chime of death about 300 miles from my house. This is what is odd. The warning appears, the tachometer rolls back, then just as it goes into limp mode for about one second the odometer rolls back to normal and the warning goes away after 10 seconds. There is no hot engine warning, it just goes straight to the “overheated engine” warning. Granted I was going about 90mph up some steep mountain passes. It seemed to happen more so going up a hill than on the flat. However I had a OBD scanner in the car and it was sitting at 210-220 degrees F according to the scanner for most the flat stuff (which it chimes about some as well). Needless to say It kept chirping at me off and on for about 3 hours and I made it home just fine. Heat works fine, when I turn on the AC the fan kicks on immediately, it has plenty of coolant. I am wondering if anyone has had a similar issue, I’m thinking one of my wires may be shorting out or a sensor is going bad. I am hoping it is not the ECU. Anyhow, if anyone has experienced this or has an idea of what it may be let me know! I would appreciate it greatly!
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Coolant sensor? Might be a cheap experiment to just replace it.
Might be worth going through the process to bleed air out of the cooling system, just in case it's all because of an air bubble in the cooling system. Seems like that could cause the symptoms the OP is seeing.

Or, you could pull the two covers off the top of your radiator and A/C condenser, to see if it's full of leaves. That never occurred to me, but when I had mine apart to do the water pump, and was shocked to find that the gap between the radiator and condenser was easily 1/2 full of leaves. Even so, my E61 never overheated in the (wickedly hot) AZ summer, but the A/C was unimpressive. This obviously happened before I bought the car, and it's hard to imagine how THAT many leaves got in there. FWIW, you can see the leaves, and the process I used to clean them out at about 8:15 on this video.
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scan tool... see what the actual temp is..

see what the status of the thermostat is

do you turn on the heat when this happens? Do you have heat?
I have heat, the overheating warning has never appeared when I had a a scanner plugged in and it always disappears faster than I could plug a scanner in. There are no permanent codes in the system. I am going to swap out my lower radiator sensor today, clean my radiator, and unplug my battery today for a few hours today. Hopefully one of the three will do something 🤷
scan tool... see what the actual temp is..

see what the status of the thermostat is

do you turn on the heat when this happens? Do you have heat?
I think thats a bad idea, You probably had a harness problem *what you need to do is view live data all the time while driving
confirm your acutal temp, and make sure you have heat when the event happens
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