Your water temp gauge will go up, you will most likely not notice until it is too late, and you will damage your bearings and or blow the head gasket, among other things.

By the time the temp gauge goes up for you to notice, the cylinder head temp will be much higher, and it may be too late. I put a scanner on my car the other day and it was reading 212*F when the needle was pegged to normal, dead center. I would not like to know what the temp was when the gauge actually gets to red. I think the engine would burn up before then.

Due to the design of the water pump mount and the problem with the impeller, it is not likely to leak beforehand as an indicator. The pump shaft is still getting spun, but it's not turning the impeller - if it is the typical plastic impeller failure.

Let Mr. BMW play fast and loose with his engine if he wants to - that is his prerogative. If your pump lets go and you lose circulation at 70mph, he isn't buying you a new motor. Unless you know for sure you have a new pump, I would change it at 70k. It's so easy there is no real reason not to - it's a $60 part, and the volume of evidence against the OEM pumps is overwhelming.

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2001 E53 3.0 5pd