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The first time I saw a mechanic using an automotive stethoscope, I thought it was over the top.
That was until I heard my engine using a stethoscope. To put it simply, it’s as if you step inside your engine. But it’s better. I can narrow my hearing to one item in the engine, eliminating other noises.
As a real example, I diagnosed an engine making a grungy/whistling noise that matched engine RPM. To narrow down where the noise was coming from, I grabbed my stethoscope.
There are several sound clips below that show the benefit of using a stethoscope to narrow in on the noise. These sound clips were taken from the engine spoken of previously.
Main engine sound (as if standing directly in front of the engine): 10+ Db during recording, no editing.
Stethoscope on top of the valve cover: 10+ Db during recording, no editing. The valve motion can be heard.
Stethoscope on top of the oil filter: This was to locate any sounds coming from the bottom-end of the engine. 20+ Db during recording, low pass filter applied to help eliminate top-end noise. I chose this location for the stethoscope to eliminate the bottom half of the engine from being the source of the noise.
Stethoscope on top of the power steering pump: 10+ Db during recording, no editing. Pumps are obviously louder than pulleys, but I still wanted to check for apparent metal-to-metal contact noises.
Stethoscope on top of the AC Compressor (while running): 10+ Db during recording, no editing.
Stethoscope on top of the failing belt tensioner pulley: 0+ Db during recording. It was deafening and the source of the engine noise. The noise was reduced in post-editing to reduce clipping/over-feeding.
Using the stethoscope, I was able to narrow down the problem in under 60 seconds. In the past, I’ve also used it to determine which spark plug wire was arcing within the valve cover. Overall, it’s an inexpensive tool that adds great benefit to diagnosing vehicles.