I just recently replaced my water pump and timing belt. As soon as i fired it up, a small amount of white smoke was coming out the tailpipe, and water was shooting a little also. The smoke and water has stopped, but now when i'm driving and the car warms up, the temperature will go back and forth between mid, to 3/4. Once i come to a stop and idle for a few minutes, it will get up to about 6/8, close to the red, but never quite touches it. I thought that maybe it was a cracked head gasket, but im not loosing any antifreeze at all. Im leaning towards a broken sensor, or thermostat. Anyone have any ideas????

The white smoke and water is just water vapor and completely normal. It happens to all cars, especially in the early morning when it is cold and humid. It should go away after about 5 minutes when the cat warms up.

Since you aren't getting any white smoke while on the throttle, and aren't losing any coolant, you could probably just flush the system really well, and bleed out any air bubbles. Try turning on the heater, and opening the radiator cap when you first start the car in the morning. If you see bubbles coming up, it's probably just got air in the lines.

Other steps are to replace the thermostat, and replace the radiator cap.

If you search for "overheating" you'll get a ton of info. The link is in my sig.

Radiator cap.

Check the area around the cap for leaks (might be older leaks so look for water stains/marks). When you get sufficiently low on coolant, you can boil the little bit you have left. The steam will sometimes blow by the temp sensor and take the gauge way up, but you won't get any heat from the heater. If your temp gauge is acting sketchy like that, I'd get a new rad cap and some fresh premix ASAP. You don't want to blow a heater hose on the firewall and have to be changing that in the middle of the night. :P Been there. Done that.

Originally posted by DR1665v2
You don't want to blow a heater hose on the firewall and have to be changing that in the middle of the night. :P Been there. Done that.

...on the highway.