Your owner's manual as you state is 60,000 miles/5 years.

 

Understood. My question is whether that recommendation makes sense at 1/3 of the mileage. A 5 year old new spark plug performs the same way as a new one.

 

If you do not follow the manufacturers recommendation you may void any warranty. If you do not occasionally change the spark plugs they may fuse to the engine and never come out. Changing them at 5 years is much cheaper then having them fuse to the engine.

 

I would personally not change plugs yet; the only risk might be plugs sticking in the heads but if you haven't operated the car in a heavy salt environment or something you are probably fine. No reasonable dealer is gonna void any warranties for spark plugs running over on time unless the spark plugs cause a specific problem and I don't know what that might be.

If you don't have an extended warranty, you will be finished with the warranty at 5 years anyway. One thought is if you possibly have leaking spark plug oil tubes or valve cover gaskets, a plug change will make these evident and you might get a warranty replacement of the tubes or gaskets.

My '09 Foz did have leaking oil tubes and the dealer put in new oil seals and gave me some new plug wires too, when I had the plugs changed. But the plugs were also at the mileage limit.

Most manufacturers have plug change intervals of 100k or 105k miles and 7 years or something. Running your current plugs out to 7 or 8 years might be a decent compromise.

For your amusement, I am attaching a photo of some spark plugs that a guy on the old Ford truck forum ran out to 429,000 miles in a commercial van. He said it was still running OK.

 

I would personally not change plugs yet; the only risk might be plugs sticking in the heads but if you haven't operated the car in a heavy salt environment or something you are probably fine. No reasonable dealer is gonna void any warranties for spark plugs running over on time unless the spark plugs cause a specific problem and I don't know what that might be.

If you don't have an extended warranty, you will be finished with the warranty at 5 years anyway. One thought is if you possibly have leaking spark plug oil tubes or valve cover gaskets, a plug change will make these evident and you might get a warranty replacement of the tubes or gaskets.

My '09 Foz did have leaking oil tubes and the dealer put in new oil seals and gave me some new plug wires too, when I had the plugs changed. But the plugs were also at the mileage limit.

Most manufacturers have plug change intervals of 100k or 105k miles and 7 years or something. Running your current plugs out to 7 or 8 years might be a decent compromise.

For your amusement, I am attaching a photo of some spark plugs that a guy on the old Ford truck forum ran out to 429,000 miles in a commercial van. He said it was still running OK.
View attachment 604495

Thanks. Helpful.

 

As others have pointed out, you do have a warranty to think about. However I personally wouldn’t change plugs at 18k miles just because they are 5 years old. I have never had a warranty on a car before either though.

 

The warranty is only 5 years. So it expires at the same time the plugs are due to be replaced. In other words, the warranty is not a factor.

 

I often like to do things based on time since I don't hit mileage for so long for instance my 2019 is at 42k I might hit 60k in 2-4 years... so I'm torn on what to do here as well-depends on the cost I suppose sadly while the dealer took care of many things on this used purchase before I bought this was not one of them-which makes me lean towards waiting for mileage

 

When it comes to plugs, I change based on time. I don't want to have plugs seized