My car just informed me at 16500 miles that I'll need spark plugs at 18k. Funny thing is, I could already feel the difference around 16300. It's subtle, but when you drive it every day, and do enough miles, you feel these things. My throttle is a tiny bit squishier than normal, the sound isn't quite the same, and I started to get the little shudder when I start the car from time to time that normally isn't there. Who knows, I may also need coil packs or something else. No check engine lights or warnings, and no loss of actual power, but I agree that 18k when you daily this car may be too long. 15k is probably the sweet spot for a stock motor.
Thanks for sharing!
