Posted under Car Engine

Cars have a language all their own. They speak to us in squeals, squeaks, and clunks. If you hear an engine knocking sound, it means your engine is unhappy and wants you to know it! Ignore the knock, and you may have to deal with decreased fuel efficiency (who can afford that?) and perhaps engine damage, which can be expensive to repair.


Knocking occurs when fuel burns unevenly in your engine. When everything is going as it should, and the cylinders have the correct mix of air and fuel, the mixture burns in a controlled, progressive manner. After each cylinder’s air/fuel mixture burns, it should create a small “shock wave” in your engine. When these “shock waves” happen out of turn and more than one at a time, you hear engine knock.


Good question! The pros at Jiffy Lube® are familiar with what causes engine knock and offer three possible explanations — and solutions!

1. Faulty spark plugs. 
Spark plugs deliver the spark that ignites the air/fuel mixture mentioned above. Because they get a good workout every time you start your car, spark plugs just naturally wear out. Their longevity can vary, depending on the type of spark plug and your driving style, but manufacturers generally recommend having new spark plugs installed every 30,000 to 100,000 miles. (Consult your vehicle owner’s manual for your car’s specific requirements.)

Why this matters: In addition to engine knock, worn or faulty spark plugs can lead to a loss of engine power and fuel economy.

What you can do: Spark plugs are affordable and readily available, so replacing them isn’t typically time or cost intensive. In fact, spark plug replacement is included with the Jiffy Lube® Engine Tune-Up Service. Trained technicians will replace your spark plugs with new ones based on your car manufacturer’s recommendations. If you aren’t sure how long you’ve been driving with the same spark plugs, visit Jiffy Lube. Regular tune-ups can help restore your car’s power and fuel efficiency as well as help prevent a small problem from becoming a costly repair.

2. Low-octane fuel.
Gasoline comes with different octane ratings or numbers. The number is a measure of the fuel’s ability to resist pre-ignition. You want the fuel to burn, but at precisely the right time, as we explained above under, “What is engine knock?” The higher the octane, the better for that controlled, progressive burn. If your car’s engine was designed to handle high-octane fuel and you substitute lower-cost, regular-grade fuel, you could be causing pre-ignition and engine knock.

Why this matters: High-octane gas is recommended for some vehicles. Drivers often choose to save money by filling their tanks with less expensive regular fuel. That’s not the best way to go! Long-term use of the wrong fuel can lead to engine knock, as well as engine damage and — get ready — decreased fuel economy. So those economy-conscious drivers may not be saving any money at all over the long run.

What you can do: Refer to your vehicle owner’s manual to make sure you are using the recommended fuel type for your car. (If you can’t find your owner’s manual, contact Jiffy Lube and a technician can access this information for you.) If you use higher-octane fuel or an octane booster additive for a few fill ups and still hear engine knock, consider bringing your car to Jiffy Lube. That knock could be your car telling you there’s a bigger problem.

3.  Carbon deposits.
All fuel sold in the United States is formulated with detergents that work to keep the engine clean. Unfortunately, carbon deposits can still form on the cylinders. These deposits can impact the air/fuel mixture, leading to incomplete combustion which can cause (you guessed it!) engine knock.

Why this matters: Carbon build-up can interrupt the combustion process, which can damage the engine’s cylinders. In addition to engine knock, you may notice lower fuel economy and a decrease in engine performance. More serious is the increased threat of your engine overheating because of carbon build-up.

What you can do: Clean the cylinders (aka the combustion chambers). If you’re not big on DIY — not everyone has the time or expertise for a project like this — bring your car to Jiffy Lube. Let trained technicians perform a complete tune-up, removing the carbon deposits to help  your engine perform at an optimal level. 


You came here for answers to questions like, “What is engine knock?” and “What causes engine knock?” That means your engine and its loud noises have gotten your attention! Why not bring your car to Jiffy Lube for a tune up? Trained technicians can tell you if that annoying knock is caused by something as simple to fix as a faulty spark plug, or if in-depth, professional attention is required.

Jiffy Lube technician talking with a woman about the cause of her engine noise


Now that you can answer, “What is engine knock?” find out why your brakes squeak when you stop.

Please note: Not all services are offered at all Jiffy Lube service centers. Please call ahead or check to ensure the service is available.