Q: Hi Patrick, I was told by my machanic when my engine light sparked in that I need a oxegen sensor, and said that it has to be fixe

Oxygen sensors are tested using an automotive scope or oscilloscope. In your circumstance, if there are more than 100,000 miles on the sensor, the sensor output should be verified on a scope. The mechanic should show you the output waveform on the scope and explain its meaning. You will see a varying amplitude signal (like a sine wave, although rough) running between about .2 and .8 volts with a transition rate (from high to low voltage) of 5 to 7 times per second. If you desire testing of the oxygen sensors, and an evaluation of the hesitation issue (which could be due to failing oxygen sensors; they do not last forever and they will often NOT set the check engine light if they are merely "failing" versus completely "failed"), please request an engine diagnostic - oxygen sensor scope testing. If you request that service, the responding certified mechanic will get this taken care of for you.

If you have noticed that the engine operating temperature is in a different range than what you have previously observed, there is probably an incipient problem with the cooling system. That problem could be as simple as a sticking thermostat, faulty radiator cap or malfunctioning radiator cooling fans. This can be checked out if you request an engine cooling system diagnostic. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.