I replaced the plugs in my X5 4.6is at 105K miles. They looked to be in fine shape. And the new ones had no noticeable effect on performance whatsoever. The originals were BOSCH in my engine and I replaced them with the NGK listed above. I would bet these plugs are good for 100K miles as well because the factory plugs were marked with the same BOSCH PN and then also had a BMW logo stamped on them. Knowing a little bit about how production control works, I find it hard to believe that BOSCH or NGK would make a special BMW-spec plug and still stamp the same PN on it. I think the 3X price is pure BMW profit margin on parts. That said, I may still replace these in 60K miles or so if I still have this vehicle and it is still in good operating condition. I hope to own it then, but my track record is not very good in that dept. so you never know.

I just picked up a 89K mile 740i that still has the original plugs. It runs great and has been getting 25mpg in mixed highway and city driving and 27-28 on the highway. So I'm thinking those plugs are working rather well. I will replace them in about a year when the car has 100K on it. I see no reason to change them early. I will probably use the BOSCH plugs this time since BMW dealers stopped using NGK. That may be for a reason - don't matter to me, both are about the same cost. I won't buy the BMW branded plugs.

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2003 4.6is - SOLD
2003 M5 Imola
2008 Mini Cooper S
2011 Mazda CX9