why change plugs when it runs fine?
Why go to the dentist before I have a toothache? Why replace my roof before it starts leaking?
If you follow manufacturer’s recommended maintenance you will have a more reliable and convenient experience with your car.
+1 to asemaster’s comments.
And, I want to add that, degradation of engine performance is not like an on/off switch, but instead is something that happens gradually over a period of time, so that it is not necessarily noticeable.
By changing spark plugs on schedule, there will likely be an improvement in engine performance and efficiency, with slightly improved gas mileage as a bonus.
With computer running the motor, performance degradation happens subtly and often goes unnoticed over time with a gradual loss of mileage. Then, in the worse situations that are most demanding, like wet weather, winter etc. you suddenly realize, 100 miles from nowhere, you should have had a tune up including plug changes when you wear your battery down trying to start your car.
I change plugs when they’re due according to the maintenance manual.
X number of miles or x number of months, whichever comes first
If somebody wants to keep their car running well, that’s the recommended way to do it.
New plugs may mean the difference between starting and not starting in cold weather. I used to change the plugs in my 1978 Oldsmobile Cutlass every fall. One fall, I didn’t get it done and thought I would be o.k. We had a temperature drop to -20 degrees. The previous year I started the car at that temperature with no problem. Standing out in -20 weather changing spark plugs is no fun.
I also change the spark plug in my lawnmower at the beginning of each season. It pays off with easy starts. My lawnmower is 21 years old and it still starts with the first pull.
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