1990 hatch, 1.5l that I have. When I bought it, the dash gauge was broke. I bought an aftermarket water temp gauge. I installed it, and was bleeding the coolant, and noticed the gauge rose to about 200 degrees and the fans never came on. Looked into it, had a cut wire somewhere, so I wired the fan to a toggle switch. I looked in alldata to see, the fans are supposed to come on at 197 degrees. When I saw the gauge reach 190 I always turned on the fan. It was ok for two weeks. Started to overheat on the way to work today. Stopped and grabbed the lower rad hose where the thermostat is, and the hose was hard as a rock. Stuck stat I figured. I put a new one in after work today, and was bleeding the coolant. Well, as it idled the temp rose to the moon, still overheating. I felt the lower hose, and it was cool to the touch but it wasnt hard. Im starting to think headgasket...or could it be that the stat I put in was defective?

 

Did you use a used stat? if not id think headgasket if you over heat driving and cool down at idle its the h.g. hows the water pump? maybe try pulling the lower hose off the rad. and flush is with water, could be clog but, not likely.

 

Did you put the thermostat in the right way?

Try idling with NO thermostat if you are sure you put it in correctly.
(BAD idea to drive continuously with no thermostat)

Feel around the front of the radiator or buy a point and shoot thermometer.
Look for cool/cold spots on the radiator - it shouldn't have any unless it's plugged.

 

also might be a bad water pump

 

got timing belt, WP and a head gasket gonna go at it saturday night

 

vent your hood

 

when the air conditioning is on the radiator fan should be on

I would fix the electrical to get the water temp sensor working first

the timing belt is not a simple job even with the right tools

 

i have seen many do this type of approach to fixing the radiator with adding extra switches and such. i would recommend trying to put everything back to original. the ecu will do what it needs to do to keep the car running cool.

as for your OH problem, you might have a warped head and/or block at this point. it could cause your OH along with a bad water pump.

 

Sounds like the water pump impeller came apart.

 

Hey guys just an update. I did the headgasket, timing belt, and water pump last night. about 4 hours of my time and around $100 and my problem is solved. I have an aftermarket gauge and the temp is between 180-190 degrees which I would assume is right on the mark for these cars. Its running great. Water pump was OK, turned out to be the headgasket after all it was damaged and exhaust was going into the coolant. I still need to de-rig my fan and get rid of the switch but honestly, it only needs the fan when it sits. My commute this morning through town and on the highway the temp never got above 195 degrees. Hopefully all is well now.

 

According to AllData, the fan should come on between 191 and 197 degrees and shut off when coolant cools to 187-181 so I would assume around 190 is the sweet spot.

 

Glad you got her fixed!