[fredjacksonsan]

Zhanks is right. There are numerous posts on some forums here where the O2 sensor failed, and the mileage went way down. The O2 code you're getting, plus the rich mixture, indicates you might have the same problem. Is the inside of your tailpipe black and wet? Getting worse mileage? If so, sounds like an O2 sensor replacement is in your future.

However, this by itself wouldn't make the vehicle overheat. I'm thinking that you probably have some flow issues with the radiator. If you take off the cap (when cold) I bet you'll see some buildup inside. A radiator shop will often flow test your radiator for you, but I'd think that after 13 years it might be time for a new one.

Once you've addressed these 2 issues, you'll probably be good to go.