- Joined
- February 2, 2002
- Messages
- 14,471
- Reaction score
- 5,289
- Year, Model & Trim Level
- 1998 Mountaineer AWD
Typically the performance will degrade so slowly you won’t notice it.For some wear items...well, you qualified it with the keyword "potentially" so I have to agree. To clarify, though, plugs and wires would not typically fall into such a category unless warning signs were present but ignored. Incomplete, uneven and intermittent ("missing") combustion will always manifest in diminished mileage. Detect this and immediately put plugs+wires on the list of potential culprits. But the proof is in the performance. If same as when new, leave 'em be! (Spend that $ on something that makes a difference.)