Just recently when driving the 1998 Cavalier,when drivingunder light - medium load, the temp gauge will start to bounce up and down and the car will have a slight hesitation. There have been no codes sent to the computer. And now that the problem has been going on longer, it seems that when you come to a stop, the gauge will slowly drop down to the first mark on the gauge. (there are only 2 marks on the temp gauge partialy warm and the one before being in the red) Then when you start to accelerate the gauge will slowly come back up to some what normal operating temps. The gauge bouncing around is very speratic, it doesnt do it all the time, only sometimes. Any help would be awesome, the car has been to 2 mechanics and neither can figure it out.

Thanks Nick

 

Check to see if the cooling system is pressurized. It sounds like there could be air in the system or the t-stat stuck open. This could be caused by a number of things,a blown head gasket, bad t-stat, or a bad pump. I would pull the radiator cap off when its cold and watch what it does during warm up. If it looks like its going to overflow put the cap back on and hold the upper radiator hose. Feel for hot fluid and then see if it builds pressure. I personally think the t-stat may be stuck open. This would allow fluid to run through constantly but cause circulation and proper cooling and warm up problems, whichcould cause some engine hesitation.

 

I had/have the same issue.

The metal line that comes off the inlet of the radiator to the water pump, leads to the heater core. If you have a hard time finding it, follow the heater core lines back to the motor and you'll come across it. On that line, there is a Bleeder. Open that while the car is first started and you'll probably see air coming out along with antifreeze. Bleed it like you would the brakes (you may have to do this a few times) to get all the air out.

My car still runs a little cold, but it's definately better since I've bled the air out of the Heater Core lines.

Peace,
Dizturbed