Wrenchin’ Wednesday: Tracking Down Unweclome Engine Sounds

Engines are heinously noisey. OEMs spend millions on R&D during development trying to hide every rattle, tick, bang, and clunk that a car tends to make as it goes about its business; but to a trained ear, those sounds can warn you about a problem before it becomes catastrophic.

A mechanic’s stethoscope is a useful tool in diagnostics, allowing a mechanic to listen to different components with pin-point accuracy. Noise is vibration, so by selectively listening to different parts and amplifying those vibrations we can determine whether a part is failing or where a specific noise is (or isn’t) coming from. This can be anything from diaging a worn out serpentine belt tensioner pulley to tracing an unwelcome engine noise to its source. You can hear rods knock, damaged lifters tap, and wore-out ball bearings rattle much clearer with a stethoscope — but more often than not, you won’t find one around the average garage or tool bag.

Instead, you can use some common items to track a noise. Any stiff bar — be it a screwdriver, jack handle, or pry bar — can be used as an improvised stethoscope if you cup your hand around one end. By touching different parts and listening to the vibrations that travel up the handle, you can quickly identify and trace most sounds of failure.

This is a good time to mention that extreme car must be taken to prevent injury or damage if you’re doing this around live electrical connections (primarily around the battery terminals, starter wiring, and/or back-side of the alternator) or moving parts (fans, belts, throttle cables). Place the tool, double check the area around the tool, and then turn your attention to the diagnostic listening.

This second method is one of our favorite ways to track exhaust leaks around gaskets: Grabbing a length of heater hose or other medium-diameter hose allows you to hear more subtle sounds (an exhaust leak being a burst of air pressure that creates the sound instead of a mechanical vibration) with isolation from the general concert of a running engine. Like a ship’s voicetube, sound travels through the hose, giving you a flexible and cheap tool for snaking around headers and flanges — even some vacuum or boost leaks can be found as they whistle along!

Wrenchin’ Wednesday is a weekly garage-hackamajig, wrenching smarter-not-harder with small tips that make working on your project easier, cheaper, and maybe even a bit faster. We’re probably not the first with any of these ideas, but you won’t be the last to know every Wednesday!

The other week, we waxed poetic about fixin’ what ya’ broke!

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