I have a 2000 Mazda Protege that last had it's spark plugs replaced about 4-6 years ago (about 40k-60k miles). It's a commuter car, but it's a short commute and mild driving conditions; probably 85% of its total miles are highway. When I replaced the plugs back then, I used Platinum (or similar) plugs, and replaced the wires at the same time. Currently I'm not having any noticeable problems (misfires, hesitations, poor MPG, etc). My questions are:
- Given that the car is running fine, is it necessary, or at least still recommended, to change them by now?
- Am I likely to see any improved performance if I do, or would it just be preventative maintenance?