What is engine knock?

Hey, what's that knocking noise in the engine? See more pictures of engines.
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At some point or another, it'll probably happen while you're driving along -- a worrisome series of sounds from deep within the engine, distinct from the typical under-hood clanks and chugs. Have you or your passengers ever wondered, "Hey, what's that knocking noise in the engine?" You've answered your own question. It's probably engine knock.

Simply naming the sound, though, doesn't tell the whole story, and you'll soon see why. There are a few reasons engine knock is so confusing. First off, the name simply sounds intimidating -- knocks are hard and often imprecise sounds, and if they're being produced by a lot of moving metal parts, that's probably not good.

Engine knock is also known by other terms, which only adds to the anxiety. If you've heard the term "detonation," it's pretty much the same thing as engine knock. If you've listened to your engine for a while and you're convinced the knock sounds more like "pinging," you'd also be correct. If neither of these phrases sounds like an improvement, that's because the noise itself still sounds scary.

And if that isn't enough to worry about, these engine problems -- whether it's an annoying ping, a persistent knock, or a dramatic detonation -- can be traced to several different sources. It's more common in some engines than in others -- some are particularly prone such problems, while others are more resistant. In this article, we'll examine the causes of engine knock and discuss some ways to soothe a noisy motor.