1999 740i expansion tank

[Tommy Boy]

I had a leak at the bottom of my expansion tank around the coolant level sensor, I replaced the tank and the problem still exists. I took a chop saw to the old one to see how it operates. It looks as if there is too much coolant in there it flows down a tube where the sensor sits and bypasses it straight out? Could it be a bad radiator that is causing the coolant to go straight to the expansion tank? All suggestions would be greatly appreciated.

[Lee]

The coolant level sensor usually has a rubber ring which can dry/melt over time. But your car, being only a few year old, should not have that problem. How big is that leak? Are you overfilling your cooling system? Even water expands and needs some room. If a cooling system keeps on leaking this way, then I usually suspect a bad headgasket that allows pressurization of the cooling system by the combustion chamber's pressure. usually, you can smell exhaust fumes from the expansion tanks.

BTW a coolant level sensor is about $30 and comes with a rubber o-ring. Not a bad idea to change it ans see if it still leaks.

[Tommy Boy]

Thanks Lee

[m.khoury]

make sure that cap is good
they have problems