A few weeks ago I wrote about a persistent overheating problem on a 91 2.1.
Since Christmas, the van has been popping this and that, including a couple
of coolant tanks. I got the problem fixed shortly after with the help of the
advice of many and one listmember who sent me a replacement heater and
valve. Here's how I figure what went wrong:

I pulled up the rear seat to its raised position and saw coolant dripping
from the heater valve. Pulling the seat to get the heater covers off is the
difficult part of the job (not really, but getting the seat back in by
yourself is) but replacing the valve is trivial. It was during this
procedure that I came to appreciate Craftsman hose clamp pliers for the
great tool that they are. No junk here.

The reason the valve was leaking was that the entire topmost surface had
been lifted off on one big chunk. I called my daughter, who had been driving
the car around Christmas time, and she confirmed that she had added water to
the tank, and then coolant the next morning. Either she was a day too late
with the coolant or she did not run the engine to mix it, as we had some
very cold nights around that time. It froze and popped the top off the valve
the size of a half stick of gum. Where it was parked, she didn't notice the
drips coming out the side of the car as coolant soaked the floor under the
seat.

The car still ran hot after replacing the valve. I removed the thermostat. I
believe it was David B who said something to the effect that "you can
consider a thermostat damaged after any overheating event." In all my years
of mechanicing, I had never thought about that. He was right. Upon
examination, the wax pellet that operates the thermostat was visible on the
outside of the mechanism. Not good. A new thermostat and o-ring completed
the procedure and the car has run at the proper temperature ever since.

Jim