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Discussion Starter #1
I hope I can get some direction. I have a 2000 328ci with 118k. Over the past year my coolant light has been coming on. I have replaced the expansion tank as well as the sensor. I have flushed all coolant and refilled. Mechanic has done a full press test on the system more than once and have not found any leaks. Left the car sitting overnight with the press test system on and once again no problems. No water in the oil so no crack in the head. Car has never overheated.

Why am I still loosing coolant? It takes about 2-3 months before I loose enough for the light to come on but its getting very annoying.

Any suggestions? Is it just time to say heck with it and replace the whole cooling system? radiator, water pump etc?

Any help would be appreciated.
 

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have you replaced your water pump? If not, it may be leaking slowly enough not to leave a puddle under the car.
 

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i have the same model around 100 thousand miles the cooling system starts going out slowly so its important to swap out the parts as preventive maintenance.. the thermostat water pump.. and not necessary but the radiator and expansion.. but if u have done it.. just go get it looked at .. or simply do the maintenance.. relative cheap if u do it yourself very easy diy
 

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Discussion Starter #4
Thanks for the responses. As I had stated I have replace the expansion tank, hoses are good, and the sensor. Had my mechanic test system numerous times. Have not replaced thermostat or the water pump. I didnt realize they start leaking slowly when they begin to go. Good info. It may be time to just go ahead and bite the bullet and replace the radiator, water pump and thermostat. I was hoping to avoid that right before the holidays but oh well what can you do.
 

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Were the pressure test performed with the engine running? The water pump may not leak much unless the engine is running. :str8pimpi
 

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Discussion Starter #7
Up till this point it has been a slow leak, at least that is what it seems, until last week when on Wed the light came on and I topped the fluid off then on Sunday the light came back on. I even pulled off the bottom shroud to see if I could see any leaks and NOTHING. Have no clue. I hope the radiator water pump and thermostat takes care of it. I just hope it is not the head gasket. Althought the car has never once overheated or had any other problems. I will give an update once I drop it off tomorrow.
 

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How much fluid are you replacing? In two to three months you probably will be a little down. Check your oil to see if it is contaminated, if it is the head gasket you may see the evidence in the oil.
 

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I had this problem. Pressure test was always ok. It turned out to be the thermostat housing. Once replaced the problem was gone.
 
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