Rep Power: 0

Hi,
98 Honda Civic EX

My car was having issues with overheating before the winter. I added about 10 ounces of coolant to it about 6 months ago and it was okay for a while. I would begin to overheat even in the dead of winter when it was 20 degrees out. The needle would almost reach the high temp of the gauge then drop back down to the middle. 3 weeks ago I replaced the thermostat thinking that it was just sticking. Then about 2 weeks after I replaced the thermostat it began overheating again. The radiator blew last week and I went out and replaced the radiator. Then my temperature gauge gets to about 1/8 warm then drops to cold when I am driving. The engine light turn on after I installed the radiator, checked it out and the error code was for an excessive reading on my coolant temperature sensor. I replaced that but the gauge still does not work. My RPMs in idle are staying at about 1500 when they used to idle at 600. I assume my car still thinks it's cold. I know I should check the head gasket and make sure the head is not warped but do you have any ideas on what could be causing a cold temperature reading?

Thanks

 
Rep Power: 518

When it has been running and you have been driving for sufficiently long enough time that the engine SHOULD be up to operating temperature, grab the top radiator hose with your hand. If you can hold on to it without flinching or pain, the engine is not warmed up. Thermostat probably stuck open.

If the top hose is hot enough to make you say "DAMN" and let go right away, then the engine is probably warmed up and the gauge is lying. You need to do more checking.

Engine computer and temp gauge use 2 separate temp sensors in the end of the head. Make sure you are messing with the correct sensor.
The sensor for the computer has 2 wires. The gauge sender uses a single wire.

 
Rep Power: 0

The hose is too hot to hold when the car is warmed up. I replaced the sensor for the computer. I didn't even know there was a separate one for the gauge itself! (Thanks) I will check that one out.