My 1992 740 wagon leaked coolant earlier today. I had the engine
running for a few minutes but then turned it off and discovered the
coolant on the ground later.

Also, the temp gauge has been in the red at times the past day or two.
I replaced the thermostat 6 months ago after the temp gauge had
stopped working. That seemed to get it working again. But recently,
the needle went into the red and stayed there when idling at a red
light. When I got home, I checked the recorvery tank. It was empty and
pressurized. The hose leading to the thermostat was hard as a rock and
hot as well, naturally. Later, when everything cooled, I opened the
recovery tank and found it was still empty but there was a large piece
of rubber or plastic inside loose on the bottom. It couldn't fit in
the hole at the bottom and, since I wasn't sure what it was, I left it
there.

Any suggestions?

Thanks in advance.

Mark