[mcmp1995]

2009 BMW 328i. Last year I noticed the engine was very hot after driving. Also I installed an Android console set, which always compain CPU overheat. So I added some coolant to the coolant tank. The next few days I noticed coolant on the garage floor. So I took the car to a repair shop. The guy said the radiator is leaking, and charged me $800 for radiator and a pipe, and said it would be three days. But three days passed he still did not give me the car, said there was still leaking and he could not found. Eventually a week later he gave me the car.

Then few days later, I drove to school, and when I park there, I notice all the coolant leaked out and all over the street. I had to tow the car back. I don't trust the repair shop anymore. So I started to repair myself. I changed valve head gasket, oil filter housing gasket, both very stiff and no good. Also I changed the micky mouse flange, which is broken inside. Everytime there will be some leaking. I was very tired of buying coolant and leak out, so I just added distilled water in it. And thought when I fixed every leaking, then add 50/50 coolant to the whole system.

The car behave normal for one month now. And suddenly when I drive about 20 miles, I noticed a lot liquid on ground. When I went home, the next day, the low coolant light is on. I open the hood, I notice the coolant tank and the big bleeder screw with cross on top has dry blueish stain on it. I bought the dye and put in tank, again put about a liter of distilled water in tank. Drive the car for 20 miles, nothing leak now.

It is so strange. I don't know why there is this intermittent leak. I suspect that maybe I put too much distilled water in it, so the boiling temperature become low, and vaper build up in tank, so it pops the bleeder screw?

Advice please. thanks!

[Suvorovo]

Can you pinpoint the exactly location where the coolant is leaking and post some pictures? From your description, it doesn't sound like the expansion tank is leaking, but the plastic tank is a common failure point. If you're seeing coolant on the expansion tank, maybe it's cracked toward the top and only leaks when you fill it up.

Maybe one of the hoses wasn't attached correctly? If your car is dumping fluid randomly, there should be evidence where that leak is happening. There aren't that many points where the coolant can leak...

Check hoses going from radiator to expansion tank, hoses to water pump, water pump itself, etc. I've heard that the water pump can crack, although uncommon.

[mcmp1995]

I put UV dye in the coolant tank, and continue driving the vehicle. One day I drive about 20miles to gas station. When I park the car, a lot of coolant went off in left front of the car. Later I put a gallon of distilled water in, and drove it back home. The next morning I jack up the car, remove the bottom plate. Surprised to find out only the radiator drain plug have the dye color on it. So I removed the radiator plug, did a search online, found that the radiator plug they put in was the short version. My car is auto-transmission, so the radiator plug should be a long version. Last year the car repair shop changed my radiator, apparently they put the wrong radiator plug in it, and caused me a whole year of mysteries coolant leaks. I went to a local BMW dealer and got a long version of radiator drain plugs for $15. And I did not have leaks since then.

Lesson learned, don't go to some store who don't know what they are doing....

[StradaRedlands]

Ohhhh, good fix! Yes, that short plug will leak on an auto-transmission car!