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Old 03-18-2020, 01:51 PM
oldskewel oldskewel is offline
Join Date: Nov 2014
Location: SF Bay Area
Posts: 1,038
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Originally Posted by Rootripper View Post
Planning on changing plugs and coils due to check engine light. Looking for pitfalls and good guidance.
Thanks so much for your help
If there is a real concern for head/thread damage when changing plugs, and the work is being driven by a CEL, I'll say the safer first thing to do will be to actually read the codes and at least confirm you've got a misfire.

You don't want to be performing a potentially risky operation at an inconvenient time when it may not even be needed. What if the CEL is for some emissions thing?

My data point on this:
2001 3.0i
replaced the *original* plugs at 169.5k miles, shortly after getting the car
No change before vs. after in terms of engine performance, MPG, problems, etc.
Removed plugs looked pretty good. I bet I could still be running them.
Am still on the original coils at 192k+ miles.

Comment / opinion / conjecture - I think that when these high mileage plugs are spec'ed at 100k miles, it may actually be effectively indefinite (comments, StephenVA ?). Changing them at 100k miles may have more to do with preventing thread damage for when they eventually get removed.

When I changed mine, they did not come out very easily, and I was extremely cautious. In addition to following StephenVA's procedure, I:
  • cleaned out the spark plug well with brake cleaner and compressed air
  • put in a generous amount of WD-40, not just a few drops
  • started with the front ones, for easier access as I was figuring things out
  • very slow and careful. If you have thread damage, the torque needed for removal will be pretty constant, as they won't actually be threading out, but after breaking it free (when the threads all strip), you'll be turning the threads against eachother with constant torque. Well that is almost what it felt like while unthreading for me, even though I did not have thread damage. After breaking free, I put some more WD-40 in the well and let it sit a while. The threads were just not especially clean and free, which is not unexpected after 170k miles.
  • I carefully installed the new ones using anti-seize, but using that may not be for everyone.
2001 X5 3.0i, 190k miles, AT, owned since 2014
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