Dear Car Guys...
I recently had a 70,000 mile tune up done on my 4 cylinder car. The mechanic recommended that I replace the oxygen sensor. Of course, I promptly laughed in his face and suggested that he might have been effected by a lack of oxygen as a little child. Can you tell me whether one of us is out of our senses?

I can assure you that your mechanic has not been spending too much time around the nitrous tank in between tune ups. Simply put, oxygen sensors are designed to measure the oxygen content of a cars exhaust gas. This information is used by the onboard computer to control and regulate the mixture of fuel and air being burnt in the engine. When the mix is proper, the engine will perform at the optimum balance of power, economy and at the lowest emissions possible. Oxygen sensors should be changed every 30,000 to 50,000 miles, or as part of a regular tune-up. Even though you might not notice performance problems, an overused sensor will cause poor gas mileage, as well as high exhaust emissions. If your mechanic suggests a new oxygen sensor in the future, and you have not had it changed before (or at least in the last 30,000 to 50,000 miles), he/she is probably very balanced and you might be well advised to have more common sense.