I replaced the oxygen sensor in my 93 Bonneville for preventative maintenance. I'm not convinced that I'm getting more power out of it, but I'm clocking the miles to see if the gas mileage improves. Hopefully it will...

I replaced it with a Bosch sensor (regret it now). When I pulled out the old sensor it was an AC Delco. The AC Delco sensor looked much more robust. It had about 8 slits in the tip of the sensor and the fresh Bosch only had 3!!!! I think I'll use it for three months until just before the warranty runs out and get it replaced with an AC Delco.

What should the tip of a used oxygen sensor look like? My old sensor was a chalky white. The white discolartion couldn't be rubbed off, it looked like it was baked on. Are there any signs to determine wear on a sensor by visually inspecting it?

Keep away from Bosch!! That is unless you want you're car to get slower. I replaced my plugs with Bosch and lost performance.

I have Delco plugs, but Bosch wires. I was surprised to see so few slits in the tip of the sensor, though.

What does the white residue mean on the old one, if anything?

If I remember right, white chalky usually means the car was running normal to lean.