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Diagnostic Tool Tips

Checking your engine's vital signs

Your engine is like your body: it usually tells you when something is going wrong. We get aches and pains; your engine starts making funny noises. Squeaking, grinding, pinging, chirping and the dreaded knocking are all telltale signs of trouble. Finding the source of the noise is sometimes very difficult under the hood with the engine running. There are so many different simultaneous mechanical sounds that isolating the problem with just your hearing is virtually impossible. So, let's play doctor and get a stethoscope.

Most automotive tool suppliers carry a medical-style stethoscope with a special sound-sensitive probe and length of metal tubing. The probe can be used to listen to internal noises, while the tube will assist in finding gasket or vacuum leaks. It's definitely a worthwhile and inexpensive addition to any mechanic's toolbox.

Probe

The probe at the end of the stethoscope tube acts like that cold microphone the doctor always presses on your chest or back, and it functions the same way. Sounds that are occurring inside the engine can be isolated and the problem diagnosed. Here we're checking for a valvetrain/lifter noise by simply placing the tip of the probe on the valve-cover surface. By moving along the cover you not only find the problem but also the location where it's occurring. A word of caution! The probe is very sensitive and you should hold the metal rod with your hand while placing it against any engine part to deaden the initial sound. Otherwise the engine noise will burst into the headset and rattle your brains. Once the tube is in place you can remove your hand.

Metal Tube

The probe can be removed from the stethoscope hose and replaced with the metal tube. This will allow you to listen to spots outside the engine and zero in on problem areas. It can also be used for internal noises, but the more sensitive probe is better for that. By passing the tube over areas like this PCV valve hose or anywhere that exhaust leakage or vacuum problems are suspected, the tube will amplify the noise, allowing you to find and fix the leak. The tube is far less sensitive than the probe and can be held directly on the block or other area without fear of hurting your eardrums. Obviously, like using any tool around a running engine, extreme caution must always be exercised.

Timesaver

Again we're using the probe to find a pesky squeak in the front of the engine. It could be the water pump bearing, alternator bearing or power steering pump bearing, but with the fan going and the rest of the ambient racket going on, good luck! By carefully placing the probe against each part because the internal sounds are readily discernable. We checked each item and determined that the water pump was the culprit. Without using the probe it would have been impossible to isolate this particular noise and would require a lot of work disconnecting drive belts, etc. to try and find the worn part. For an investment of around twenty dollars you can play doctor too and simplify finding problems like these.