And they're almost always 30K miles past worn out when you do. They're fun to get out of the head, too. It's a really stupid idea, no matter what anyone tells you, ignition system components do not have anything near peak efficiency and quality past 50K miles.
If you're one of those unlucky souls, it'll cost you about as much to get a seized plug out of a cylinder head at 100K miles as it would have cost to have the vehicle tuned up 3-4 times.
This ^^^
Aluminum heads and steel plugs dont mix well and once seized they tend to remove the threads with the plug.Oh it's a simple enough fix but like capt.Virgil says the cost is likely way more than changing out the plugs 3 or 4 times.
Funny how the plugs last the same length as warranty...
Thats so the manufactures dont have to spring for the head removal and helicoil and associated machining.
I had the plugs done on my honda at 40k,werent due for another 60k but the service manager and I are friends so I said just do it. Later he said to me,good thing we changed them,1 was almost seized and had I have waited I would have been facing a nice bill to repair it. The service manager told the tech to be sure to use plenty of antiseize but even that wont help much after 4 or 5 years! Oh and I plan to replace them again at about 80k!!!