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Thread: Pre-emptive spark plug change

  1. #1
    Vulture of The Western World Eric's Avatar
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    Pre-emptive spark plug change

    Modern engines run so efficiently that recommended spark plug changeout intervals are sometimes as infrequent as once every 100,000 miles. Even 50,000 miles is about 4-5 times less often than was typical of cars built during the '60s and '70s.

    But, there's a catch.

    If you leave the plugs in the engine that long, it may be very hard to get them out without damaging the engine - specially if the engine has aluminum cylinder heads. What happens is the plugs fuse to the threads in the head and when you try to turn them out, the threads in the head come out with the plug. Often, the only way to repair this is to remove the cylinder head from the engine - a labor intensive and expensive procedure. All because of a $2 spark plug.

    So, while the engine may not need fresh plugs before 50,000 (or even 100,000 miles) it is a smart precaution to have the plugs removed more often (once every 30,000 miles is a good yardstick) and reinstalled with anti-seize compound on the threads. This will avoid future problems getting the plugs out safely - and you can also use this as an opportunity to check the condition of the engine and how it's running by reading the plugs. They can also be cleaned and adjusted (re-gapped) or replaced, if need be at this time.

  2. #2
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    Changing plugs early can also prevent the coil packs from prematurely wearing out. As electrical parts age, their ability to dissipate heat diminishes. Heat degrades the electronics, including coil packs, inside the engine.

    The only disadvantage of frequent changes is that sometimes intakes must be removed from the engine to access the plugs. As a result, you may add to the premature wear of the gaskets, hoses, etc by removing the intake more frequently than recommended. Therefore, I wouldn't change plugs more than every 50-70,000 miles.

  3. #3
    Senior Member DonTom's Avatar
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    Quote Originally Posted by Eric View Post
    What happens is the plugs fuse to the threads in the head and when you try to turn them out, the threads in the head come out with the plug.
    You forgot to mention to only remove the plugs when the engine is ice cold, such as in the early morning before any use. This alone should help prevent such problems.

    -Don-

  4. #4
    Vulture of The Western World Eric's Avatar
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    Quote Originally Posted by DonTom View Post
    You forgot to mention to only remove the plugs when the engine is ice cold, such as in the early morning before any use. This alone should help prevent such problems.

    -Don-
    Yes, good point!

    With alloy heads, you've got to be extra careful - both removing and installing. It's pretty easy to cross thread (especially when you can't install the plug by touch, as when it's buried deep in the cam cover as on many modern engines) and also to overtighten. Either screw up can create a big problem!

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