Why would a 2001 Cavalier run hotter than it used to - from 195 to about 210?

More than likely your thermostat is beginning to go out. If the temperature keeps climbing, it means that the thermostat is stuck closed. It will only get worse over time. Thermostats are not generally expensive ($15-$20). To find your thermostat, follow the upper radiator hose until you see where it meets the motor, and the thermostat is there under the housing. Just be careful. When putting it back together, if you overtighten, there is a chance that you can bust the housing. I would suggest getting the torque specs for the car before doing any work. Good luck. Another possibility is a headgasket starting to leak. As the piston compresses and combustion take place, it may be pushing hot exhaust gases into the coolant raising it's temperature. Also, the gauge may be inaccurate, a shop can use a scanner to tell the actual temp, and compare it to your gauge. A coolant temp sensor for the gauge may be faulty. There may be a air pocket. There may be a light coolant leak, is your level low? My Cavalier started to go up in temp. It would "hunt" between 190 and 200 degrees. I put new Bosch spark plugs in and the temp stabilized at 192 and never rises above 195 even when idleing. The plugs (AC) that I took out looked fine except that the tips of the electrodes were rounded. Time and miles will do that. The Bosch plugs were double platinum and never need gapping. They promise that you will see better performance and gas mileage and easier starting. Mine always started good but the best side effect was the evening out of the temp guage. It is my opinion that the more even spark allows the gas and air mixture to burn more evenly and thus the cylinders and such stay at a more constant temp. The plugs run about $7.50 per PAIR. However Bosch guarantees that if you do not see a marked improvement, they will buy them back. So you might try putting new Bosch plugs in and see what happens. You have nothing to lose and everything to gain. You can always get your money back. Hope that helps..