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I desperately help from an expert please. I have had a problem with my 2007 BMW 550i Sport since I purchased it about 14 months ago. The underlying problem is that the car will intermittently overheat when in traffic or when idling in hot weather. The only thing I am sure of is that the engine-cooling fan does not always engage when it should and consequently the a/c will not function properly and the car will overheat.

Since I did not purchase the car from a BMW dealership, I initially took the car to 2 different independent BMW mechanics. The first mechanic replaced the fan but it did not fix the problem. He then replaced the oil temperature sensor but it also did not fix the problem. I then to took it to another very reputable BMW mechanic who diagnosed it as needing a new DME unit. Due to the cost involved, I called the dealership for second opinion.

The dealer indicated that the DME unit on my car had a warranty up to 80,000 miles. This encouraged me to bring the car to the dealer for servicing since my car only had 70,000 miles on it at the time. After testing my car, the dealership indicated they solved the problem by replacing the coolant temperature sensor rather than the DME.

A few months and 20,000 miles later the same problem occurred. This time they said the IVM and a cable related to it needed replacing and their top mechanic was sure this was causing the problem, so I authorized the service. A few weeks later the same problem occurred and the car has been at the dealership for over month with them just scratching their heads. Fortunately, they have given me a nice loaner car to drive for free so I have been very patient.

Some important things to note are that neither the dealership nor the independents have been able to recreate the problem but they have seen the engine temperature high codes. Also, both the second independent and the dealership determined the ground signal was not always going to the fan when it should which led the indie to believe it was the DME. Interestingly, the dealership continues to be adamant that it is not the DME because they have thoroughly tested it. I am not sure if the dealership is trying to avoid eating the cost of a DME because they should have put it in when it was under warranty, or if they are simply baffled. Finally, I have contacted BMW USA and they said there is another level I can take the car to if the dealership can’t solve it.

Sorry to ramble on, but as you can see this has been a nightmare with no end in sight other than trading for a Honda. Any insight would be greatly appreciated.

Thanks for listening.
 

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This isn't expert advise but from experience dealing with a couple of different dealerships I would try another and if not raise some hell to bmwna... When u put your car in there hands u shouldn't have to worry about the same sh*t happening over and over... Goodluck let us know how it goes...
 

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I know the feeling of helplessness. Though I did not suffer from the same problem, but I had a fair runs to mechanics and BMW dealership for an engine vibration thing. I ended up contacting BMW Germany in an email and I did it in complete hopelessness as I had decided to sell off my car and get a Lexus. To my surprise, they replied back apologetically and then the Service Manager of BMW Saudi Arabia contacted me to bring my car to the dealership without an appointment. They gave me a nice loaner for a week and they had fixed the problem. Not sure this is going to help. But I wish you all the luck!
 

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OP,

May be you should also post this at other forums too to see if anyone ever experienced similar problem. Try the 5series forum and look for turboawd. He seems to know a lot of things when it comes to the coolant and fan issue.

GL
 

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How often this overheat happens? if it's rather predictable, I'd ride with foreman shop and show it to him when it happens.

At this point, none of us is expert compare to dealer tech. Your situation is not common, "overhat only in hot weather" which point to aux fan not kicking in when extra cooling needed. Well, I assume the shop probably already check the motor, wiring, sensor, cause those are the easiest to test. the last piece would be DME, the one that provides the power to the motor through transistor/FET, if you have bad or cold solder in the PCB of DME (very rare but happens to all electronic products) then that can be intermitent, not to mention if you have transistor/FET that gong bad in DME. Unfortunately, dealer can't just swap DME to see if the problem go away so be persistent, at least you have a loaner. GL
 

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did you try replacing the coolant thermostat? it should be an inexpensive task to do. just my 2 cents
 
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