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    Member No: 188430 chuck2339 is an unknown quantity at this point chuck2339's Avatar
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    When is it time to change spark plugs?

    2005 325xi - 80K. How much milage should a set of plugs endure under normal driving conditions? What are the symptoms of worn plugs?
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    Officially 100K miles.
    My opinion; you're due now.
    Want your plugs to be working peak efficiency.
    And if left too long, can damage the threads getting the old ones out. Search for DIY to learn what you need to know.
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    I changed plugs on my '04 330 xi around 90k and it made a huge difference. Engine was running a bit rough at idle and gas mileage was getting worse. You won't regret it.
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    I changed mine at 80K, when my valve cover gasket started to leak oil.....

    Although, the car was running fine and and when I pulled the plugs they looked OK as well. My advice is if you are DIY'ing this then you might as well do the valve gasket while u got full access, this gasket is notorious for leaking after 80k. Check the wires and coils as well.
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    On an e46, modern platinum and irridium plugs last a very long time. However, it is tough to tell by looking at them when they are past their peak. They don't have square shouldered center electrodes that get rounded, or an over-reaching side electrode that get pitted.

    Also even nickel plated plugs tend to weld themselves into aluminum heads after a lot of thermal cycles and a lot of sparks. Folks who run their plugs 100k miles sometimes run into that problem.

    If you use anti-seize to try to prevent the plugs from bonding to the head, be sure to reduce tightening torque. The lubricant means that the plugs pull harder on the aluminum threads at the same torque setting.

    I like to replace my plugs at about 50k miles, and I don't use anti-seize.

    As for symptoms, with good quality (i.e. Denso or NGK) platinum or iridium plugs, I would not expect to see symptoms from worn out plugs until 100k miles or more. Worn plugs will tend to accentuate whatever other problems you may have. The rough idle from a vacuum leak will be worse with old plugs. The misfire at high RPM and full throttle will be worse if the plugs are worn and harder to fire. Of course, this implies that if the car runs better with fresh plugs, you may not have corrected the root problem. I had a Volvo with a warm start stumble/stall problem that would go away with fresh plugs. After years of replacing plugs more often than I should have, I figured out that I had an inaccurate temperature sensor in the head.
    Last edited by Manolito; 10-19-2014 at 05:35 PM.
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