radiator coolant leak

[bimmerted]

This forum has been very helpful in diagnosing/repairing a stall problem on my '98 1.9 Z-3 (turned out camshaft position sensor). Well this 10 year old is showing a new problem. The shield below the radiator has evidence of radiator coolant leakage. I did a brief look underneath and it seems the leak is at or around a large black plastic bolt (same side as filler cap/expansion tank) . Does this sound familiar to anyone? It can't be much of leak (yet), I'm only down a few hash marks from the recommended level; no CEL; and temp guage is dead-center throughout drive.
Ted

One other Q comes to mind. Is it recommended to spray silicone on the inside of ICV/idle control valve after cleaning?

[marti5]

Is the big large bolt, under the expansion tank or next to it???

If in the exp tank, its the coolant level sensor, can fix with new rubber 'O' ring.

If next to tank possibly drain plug, normally fibre washer.

[bimmerted]

Marti,
Standing in front of the car, the bolt is black and directly below the expansion tank (on a Z the expansion tank and radiator are integrated) on the right side. The drain plug is blue and on the left side. Is the sensor at the very bottom or side. I would imagine it has a wire or two coming out of it.
I suspected an o-ring as the car spends a lot of time in storage. I HOPE that's all it is. Thanks.
Ted

[marti5]

Yes, the sensor will have wires coming from it, I would change the 'O' ring and see how it goes, like any car standing around for a time things seize up and rubber esp just goes.