I see two sending units, one under the distributer and one on the coolant inlet. Which one feeds data to the temp guage on the dash? The guage doesn't move, it stays on cold just like if the key was turned off. Any other suggestions other than sending unit? EDIT: So now that I replaced the sending unit my guage started working, only to find that it peaked out on hot. I wasn't patient enough to let it completely cool down before I replaced it but I drained the coolant out through the radiater. My fans aren't kicking on but the car also doesn't APPEAR to be overheating. No boiling in the overflow, motor doesn't seem ridiculously hot. Could it be air in the system?


Modified by littlejon at 11:14 PM 10/2/2008

 

The sensor under the dist. is a one wire sensor that goes to the instrument cluster and the other is a fan switch to the computer which turns on the fan.

 

What's the best process for bleeding the coolant system of air?

 

there should be a small nut/port on the neck where the upper radiator hose connects, you open that with the car running. air will go out through that hole.

 

Is it true that air in the system could send a false reading to the sensor, therein not allowing the fan to kick on?

 

the fan should kick on but yes it can give a false reading and make your idle fluct , try leaving the radiator cap off and let it run and have all the bubbles out of the system

 

if there is an air pocket in the system the temp sensor can read lower than what it really is at.

remove radiator cap and run car with the heater on to flow coolant through the entire system.

also if the fan doesn't come on check the fan switch, pull the connector off of it and use a jumper wire to connect the two pins on the connector to eachother and the fan should start. if that works and not with it hooked up to the sensor replace the sensor.

 

The fan is now kickin on but way too LATE. It'll kick on at about 3/4 on the temp guage. Should I replace sensor? I left the cap off for about 10-15 minutes.

 

have you checked for a bad thermostat, or one that is set at a higher temp to open.

I just replaced a head gasket on a 93 hatch sohc non-vtec that was doing the same thing but it would run fine and over heat about 3/4 on the gauge then the fans would kick in. his over flow bottle would raise its level every 250miles or so but would not boil. I did a block test were you check for exhaust gasses in the coolant, and it failed. After replacing the head gasket the problem went away.

 

when you left the cap off where was your heater/ac control set to? move the lever all the way on hot. you dont have to turn it on but move it to hot. air gets trapped in there and the coolant does not get bled properly when it is on cold. just a quick suggestion.