Hello fellow list members - I am in need of some technical support for
 my '90 Syncro 2.1. I just finished replacing my exhaust system (long
 story, for another time) and now my coolant temp gauge warning light
 begins flashing about 10 seconds after I start the engine and does not
 stop. The engine can be hot or cold, same result. The coolant and
 overflow reservoirs are both full. Any flashing I refer to is not the
 self-test flashing when you start the engine - that occurs normally.

I performed the following troubleshooting steps with a cold engine:
1) Disconnected coolant reservoir sensor lead - no effect on flashing.
2) Disconnected coolant reservoir sensor lead and bridged contacts - light
 flashed constantly - no 10-second delay after starting engine.
3) Disconnected single-wire temp sensor lead (bottom of thermostat housing)
 - no effect on flashing, temp gauge does not register.
4) Disconnected sensor lead (side of thermostat housing) - flashing stops,
 engine idle increases.
5) Disconnected sensor lead (side of thermostat housing) and bridged
 contacts - no effect on flashing, engine idle decreases.

Based on that I'd conclude that the sensor in the side of the thermostat
 housing is bad. I don't think it's a wiring issue because bridging the
 contacts did have an effect. What do you all think? There aren't any other
 things that could make that light flash - are there?

I did have to use a torch to loosen the exhaust bolts, and I was very
 careful to shield everything nearby with pieces of sheet metal, but perhaps
 the sensor is a little bit fragile and didn't like the heat? Just a guess.

Assuming my conclusions to be correct, my next question would be... if I
 unscrew that sensor, how much coolant is going to come pouring out? And
 will I have to spend all day trying to get air out of the system?

Thanks very much in advance.

Doug Fitz-Randolph
Freeport, ME
'90 Syncro