Ok I've got a 1993 'Lude that was modified pre-purchase, originally a non-VTEC, it now has a F22B1 Accord motor in it, for part information. Regardless, I just put a new transmission in it and when I got it back from the shop, with coolant in it, it started running hot - the temp gauge inside (digital) will reach about 1/2 way then the check engine light comes on and the gauge doesn't rise anymore... even if I hear water bubbling when I stop the car. I've replaced the thermostat and the seal, thinking that was the problem. The water pump is good, I know that. I've heard it could be the coolant temperature sensor, but what do you think, and where would that sensor be? From pictures I've seen online it resembles a piece I saw in the same housing as the thermostat, which makes sense. Also, the prior owner of the car had a wire running from the solenoid housing to the thermostat housing... any clues as to why it was there?

 

More than anything it's an old & flaky Coolant Temperature sensor & is your fan running constantly? If is, then change it out, this should fix it.
It may look like this >>

http://www.carpartswholesale.com/par...re_sensor.html

 

Do you mean that yes, you do hear water "bubbling"?

If so, you have air in the cooling system. Try bleeding it.

 

let me restate that - the temp gauge doesn't rise beyond 1/2 even if my overflow begins to steam and I hear water boiling... and the cooling fan isn't coming on at all, of course it's freezing here right now so...