There are a lot of parts moving around in today’s vehicles engines and sometimes they create noises that you should be paying attention to. To help you out, we have compiled this quick guide to diagnosing common engine noises.

Crankshaft Knock

A crankshaft knock is the most dreaded noise an engine can create. It’s a sharp, rapping sound that gets louder when an engine turns quicker.  When you hear a crankshaft knock, it usually means an engine is about to stop working.  If you hear a loud knock coming from the engine, it’s likely a crankshaft knock and you need to have a mechanic look at it immediately.

Valve Noise

Exhaust and intake valves are metal, mushroom-shaped objects that move up and down in an engine to allow fresh fuel in and exhaust gases out of combustion chambers.  The valves themselves typically don’t create noises but the tappets (part of the “valve train”) and rocker arms do.  When the rocker arm and tappet noises are loud, they “chatter”, and it almost always means that the valves just need adjustment. Technically, the chatter sound is half the speed of the engine’s flywheel and pistons.  You can always hear a little noise in a running engine but if you hear loud clicking sounds, visit your local dealer and have them take a look.


Detonation is when the fuel-air gas mixture in your engine is ignited before it should be. It is a sound that you will hear when you are driving, usually when going up a hill. Detonation sounds are like that of a metallic rattling, they are very noticeable. The important thing to be aware of is that if it happens for too long, it can cause serious damage to your engine.  Never ignore an engine that detonates for more than 5-10 seconds. Detonation is usually caused by running an engine on too low an octane level.  Vehicles with high compression levels need higher octane levels so if you think your engine is having detonation issues, try increasing your fuel’s octane level next time you fill up. Sometimes that is all it takes to fix a detonation issue.

Piston Slap

A muffled, hollow, nearly bell-like sound is typically a piston slap. This is caused by a worn piston rocking back and forth in its cylinder. Piston slap really only happens when an engine has a lot of mileage on it. A non-stop piston slap means the engine needs service; however, if you only notice the sound when the engine is cold, it is likely not serious. Unless you’re a mechanic, piston slap is a hard sound to identify.

Hissing Noise

Have you ever heard  your engine “hiss” while you are driving the car, but particularly while you are idling it? It is not a pleasant noise. However, it is a warning sign that your vacuum line may be damaged, and result in your “Check Engine” light coming on. You may need to get lines reattached, or perhaps get a new vacuum line.


As we discussed earlier, identifying engine noises can be hard for the average motorist. If you suspect that you have an engine noise that’s out of the ordinary, it is best to stop by your local automobile dealer for diagnosis.  Because they work on cars all day, mechanics have ears that are more finely tuned to sounds that occur in engines than we common folk do. A great mechanic will usually be capable of figuring out any engine noise fast.

Article Courtesy of: Thomson Dodge Chrysler Jeep Ram