corollacoaster (#29) is correct. I bought a used 2007 Matrix and waited until ~100k miles to change the plugs, the process of 'seizure' had begun. I sweated bullets as I exerted more and more force on my ratchet, there was some creaking but the plugs all came out. The problem is that the steel gasket on the plug is crushed into the aluminum head, in very close contact. Aluminum is higher in the metal activity series than iron so galvanic corrosion occurs, sometimes it seems as if the plug's hex bolt washer has been welded onto the head.
The following is controversial but upon re-insertion, wipe anti-seize on the threads, start two threads back from the end to avoid burning and use a very thin film with a q-tip applicator; also, wipe a thin film on the washer, remember that the spark plug is electrically grounded by the washer and too much grease is an insulator. On my Yamaha outboard (even with anti-seize) the spark plug washer corroded tight, I snapped the plug ceramic off, now there was a ripped sheet metal hex 'bolt' stuck in the head. Next, an 'easy-out' snapped inside the remaining pipe bore of the spark plug. I have removed that engine head and I am pondering how to get the threaded spark plug pipe out without destroying the threads on the head.
Don't risk it! Loosen and tighten the spark plugs every 20k miles. Some people do not like the anti-seize modification, but I have performed four spark plug changes (400k miles on two Matrix cars) with no problems, you must use a very light anti-seize coating.
