Hello,

I have a 99 S80 with 135k miles and I have 60K miles on the Spark Plugs. I know that they are suppose to be replaced every 30k miles but the 60K miles on the spark plugs are all highway miles. Does that make any difference that they are highway miles or not. And if I delay the replacement of the spark plugs, can that cause any harm to the engine. The current spark plugs on the car are Autolite double platinum spark plugs.

Thank you

 

Some claim they might last 100,000 miles but I have never seen any plug last that long.

In my opinion I would change them soon. If they fail you will get a Misfire. If you keep driving with a Misfire it will cause some damage to the engine not to mention poor fuel milage.

 

Thank you, and one more thing I want to ask you, would you recommend me replaceing the coils or the wires when I replace the spark plugs.

 

If the coils are OEM inspect good for cracks. If they are cracked I would replace them soon.
Cracked usually = bad shortly after.