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    What causes a spark plug to blow out?

    Spark plug blow outsDennisB © Summary: In this article we cover a common question about what causes spark plug blowouts? I’m a Master Auto Tech and have been selling permanent thread repair kits for the common Ford spark plug blow out problem since 2005. I recently came across a few sites online attempting to explain “What causes a spark plug to blow out?”. Some of the articles I looked at were written by vehicle owners that have had one experience with a spark plug blowout. Some articles were written by copy writers that wrote enough related keywords to garner results from anyone Googling the problem. Well as I said, I’m a technician that knows more about this issue than most people you’ll run across online or elsewhere. OK enough about me, let’s first cover some of the theories out there.

    • Some say aluminum heads are to blame. Well aluminum is softer than cast iron. But why then is it usually Fords that have the issue? Why don’t we hear about Chryslers and Honda engines spitting out spark plugs? We have kits for those too, but usually that’s because their threads were damaged from cross-threading. Not the typical Ford spark plug blowout that we hear about that occurs while driving down the road.
    • Some say, it’s because Ford only uses 4 or 5 threads to hold the spark plug from the factory. That’s true in some cases, but we have had plenty of failures reported to us from our customers that had fully threaded spark plug holes as well.
    • Some copy writers that I’m positive, have absolutely no automotive experience, mention an electric charge when the spark plug is too tight somehow damaging the threads…. OK, I’m scratching my head over this one, because there’s no logic to that statement. First off an electrical charge capable of degrading aluminum can occur in my experience only in fluid, like coolant. It’s called electrolysis and it can erode away metal. Usually caused by voltage being present in the coolant. You can actually test this with a meter. More than a 1/2 volt there’s potential for a problem. It’s one reason to change your coolant at the recommended intervals (or maybe even a little sooner). I’ve personally seen leaky head gaskets due to electrolysis. But it will not cause spark plug blowout!
    • Some say to check the torque on the spark plugs every 5,000 miles. Are you kidding me? Who does that? They may have accidentally stumbled upon the real area of concern though. A loose spark plug, especially one that is held in above with an ignition coil can vibrate and damage aluminum threads. It actually would do less damage if it were allowed to back on out without being held by the coil. So a loose spark plug is the most common cause of a spark plug blowout.

    When a spark plug lets loose on a COP (Coil Over Plug) you may think someone is shooting at you! Here’s what a recent customer had to say about his spark plug blow out, when the sparkplug shot out like a bullet and broke the ignition coil in the process.

    “It startled me when it happened as I was beginning to accelerate from a traffic signal when the spark plug blew out! Sounded like a gun shot and it freaked out the motorist in the right lane next to me.”

    We handle problems like this every day (even after parts store kits fail). And unlike many sellers online, we have hands on experience so we’re better equipped to help our customers find the best spark plug thread repair kit. We also email “Tips” when a blown out spark plug thread repair kit is purchased from or Just write the word “Tips” in the comment section when checking out or if ordering by phone just ask us to email the Tips. Have questions about spark plug repair? Give me a call at 1-800-734-8665.

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