1997 Honda Accord

1997 Honda Accord 201000 miles

I have 1997 Honda Accord. Just over 200,000 miles. It was one owner before who was family so I know it was well taken care of. I purchased it a little over a year ago. I have two issues/questions. The first being, when it's extremely hot outside, as in 90+ degrees and I drive it for any lengthy amount of time. Usually 30 minutes or more, when I turn the car off it takes about 5 minutes for the fan to go off. Why is this? And, also, when driving and then turning it off it smells like it's overheating. A burning smell almost. The car is not overheating though and my oil is fine. It's not low and its not due to be changed for a few hundred more miles. Is this just issues of an older car with high mileage or is something wrong. I do know that I need a new o2 sensor. The check engine light has always been on and I had it ran on a machine and was told it was the oxygen sensor. I know this effects gas mileage etc. But was told that it would not "hurt" my car in driving without replacing the o2 sensor. Thanks