Temperature gage?
 

I have a 2001 Honda Civic that has about 147,000 miles on it. For the last few months the temperature gage has been going up and down. I was told it might be the thermostat so I first replaced it and the same problem occured. The temperature gage goes from cool to hot in a matter of seconds. It goes all the way to the red. However the car is not overheating. So then I took out the thermostat all together. And the problem exisits. It does not happen every time I drive the car and there is nothing that I can tell that brings it on like sitting for a long time or the temperature outside. What could the problem be? Also the check engine light goes on and off. Stays on a few days then goes off. Someone said that it may be a bad radiator cap. Is that a possibility