I used the NGK listed first. Installed them at 64k and am nearly at 100k with no issues. Easiest plugs I've had to change.

But how would you know if you had an issue? I find it very hard to believe that any quality plug that meets the specifications would perform perceptively differently from any other plug.

Easy, keeping track of mileage are fill ups. I also use an Android app called Torque to run diagnosis monthly. Including engine mapping.

Were you able to detect any difference relative to the plugs that were installed at the factory? I'm just extremely skeptical that unless one installs plugs that are woefully off base in terms of specs, that it's possible to tell the difference between some of the high-dollar plugs available for this car, and something more affordable. Now, maybe in terms of longevity, I could believe there could be slight differences, but in terms of power, smoothness, gas mileage, etc., I doubt it.

Just adding my 2 cents as I'm researching a starting issue my X5 is having and ran across this post. While it seems this post leans towards the NGK Iridiums I didn't see anything mentioned negative against the Bosh... so...

Owning an M5 and previously a 540 with the same M62 engine as the X5 (98 so no vanos... but still) the advice on Roadfly back then was to stay away from the Bosch plugs as they tend to back out (not sure if this was common on the I6, but for the M62 it sure was.)

My personal story regarding this is I'd replaced mine way back when with the Bosch plugs and after some time (too many years ago, so I don't remember how long) my engine developed a ticking sound. I asked a few mechanic type people and the forums and they though I had a stuck lifter which would require a major repair. Anyway, I lived with it for a while and eveutally sold the car to a friend making him well aware of the potential lifter issue.

Long story short I get a call a few days later after the sale and he'd gone in to replace the plugs and found one of the bosh plugs had backed itself out and was sparking against the block. After replacing the plugs the tick went away.

I'd think this was an isolated case, however, it seemed to be common on the Roadfly forums. I'm suprised it hasn't become common knowledge here... maybe the 4.6 and 4.8 engines don't see this problem...

What is the iridium model to my 4.8is 2006?

NGK - BKR6EIX