What Is Engine Knocking & How Can I Fix It?

What Is Engine Knocking & How Can I Fix It?

| By: Christian Brothers Automotive

Knock, knock. Who’s there? Cargo. Cargo who? No, car go “beep.” Yeah, that’s pretty lame. You know what’s worse than a bad Knock-Knock joke? An engine knock.

What Is “Engine Knock?”

Do you hear what I hear? Got a strange clunking or knocking sound from your engine while running? This is called "engine knock." While it's become increasingly rare in modern vehicles, it's still a common issue drivers face – and a hard one to determine the cause for and fix.

Whether it's happening while your engine is idling, accelerating, coasting, or all three, one thing is certain: excessive wear and tear are being placed on your engine. This can lead to safety concerns, poor performance, and even engine failure, which will be very costly.

This is why it’s important to try and identify the cause of your car’s engine knocking sound and fix it as soon as possible, and it’s whyChristian Brothers Automotive is here to help. In this blog, our expert technicians will discuss what causes engines to knock, some possible solutions for your knocking engine, and what you can do to help prevent it in the first place!

Why Is My Engine Knocking?

Hearing a knocking sound in your engine can be unnerving, especially if you don’t know the cause. Don't panic, though – likeother common engine problems, it doesn't have to mean the end of your car. More likely, something in your engine isn’t working correctly and must be repaired or replaced.

We’re going to spend a few minutes with you covering 4 possible reasons for engine knock.

Engine Oil Level/Quality

First and foremost, it is important to check your engine oil. A lot of internal engine issues are due to a lack of lubrication. You will hear us stress time and time again the importance of an oil change. It is important to stay up to date on your oil changes to insure your car is running smoothly and to prevent any damage to the components of your engine. If you are experiencing engine knocking and have not had an oil change in a while, it may be a sign you need an oil change.

A Bad Air-Fuel Mixture

Your engine needs two primary ingredients to create power and propel you forward: air and fuel, and when it comes to engine knocking, a bad air-fuel mixture can be one of those 4 possible reasons. This bad air-fuel mixture can go one of two ways:

  • An air-fuel mixture that is too lean (too much air and not enough fuel) can cause the engine to knock or ping. This is because the lean mixture burns hotter and faster than a properly balanced mixture, which can lead to premature ignition of the fuel in the combustion chamber.

  • An air-fuel mixture that is too rich (too much fuel and not enough air) can also cause knocking by creating incomplete combustion and leaving unburned fuel in the cylinder.

How to Prevent Bad Air-Fuel Mixture

To avoid these issues, it's important to maintain a proper air-fuel ratio in your engine. The ideal ratio will depend on your vehicle and driving conditions but generally falls between 14:1 and 15:1 for gasoline engines.

A good way to promote proper air-fuel mixture is to regularly check and replace your engine's air filter every 12,000 – 15,000 miles or sooner if needed. Make sure you also keep up with routine maintenance likespark plug replacements.

Do Air-Fuel Mixtures Go Bad on Modern Vehicles?

The timing on modern vehicles is computer-controlled, and the air-fuel mixture is adjusted instantly to ensure the best horsepower and performance, making fuel-related engine knocks almost unheard of.

Here’s another one:

Improper Fuel

One of the reasons you could develop a fuel-related knock problem is that you’re using a fuel that doesn’t have the required octane for your vehicle. Many high-compression or high-performance engines require premium fuel to run as intended. Many vehicles, though, can operate correctly with regular unleaded fuel. Diesel fuel will greatly harm a non-diesel engine. “Correct fuel” is a thing.

Switch to the Proper Fuel Octane

You should immediately switch over to the recommended octane for your vehicle. You’ll likely still need to bring your car in for service to ensure no damage has occurred to the fuel system and engine. If damage has occurred, addressing the issue immediately could prevent the damage from getting any worse.

One more!

Worn Engine Components

Aside from a bad air-fuel mixture or incorrect fuel in the tank, worn or damaged engine components are another common cause of engine knocking. Belts, bearings, and crankshafts are among the parts that could cause that engine knocking sound. All of these parts wear out over time, and if they do they can cause the engine to make strange sounds.

A brief word about each…

Timing Belt

The timing belt controls your engine's crankshaft, pistons, and valves and the rhythm in which they move. There’s a tempo or speed at which these parts have to move together in order to work smoothly and seamlessly. The timing belt literally keeps them running and operating at the correct tempo. If worn or broken, these components can get off their proper timing, and this will cause engine knocking.

Over time, your engine’s rubber belts stretch, corrode, and wear out, usually to the point where they snap, so it's important to replace your timing belt at your manufacturer-recommended interval to prevent this from happening.

It's best to trust major engine services such as this to expert technicians. Not only do timing belt replacements require extra knowledge or skill, but it’s also an integral part of your engine and needs to be done correctly.

Engine Bearings

Engine bearings are the metal surfaces that separate your engine’s moving components, such as the crankshaft and pistons. Over time, these bearings can become worn out and cause engine knocking by becoming misplaced or dislodged due to vibration or other faults within your engine.

If left unchecked, it can lead to a range of other issues besides engine knocking, such as oil leaks, loss of power, and other breakdowns. If you suspect your engine bearings are the source of your knocking sound, it's time to have them inspected and replaced. May we elaborate?

Replacing engine bearings is a labor-intensive repair that requires sound knowledge, specialized tools, and lots of time. Because it is such a complex repair, we highly suggest relying on an experienced professional for this service.


A third component that, if worn or damaged, could cause engine knocking is your crankshaft. If it is cracked or broken you’ll definitely hear some wild sounds from your engine. Why? The crankshaft is a key component of your engine that converts the up-and-down motion of the pistons into rotational motion that powers your vehicle.

When the bearings on the crankshaft become worn or damaged, it can cause excessive vibrations and knocking sounds, eventually leading to catastrophic failure. The saddest diagnosis our technicians have to give is a dead engine that needs replacing, as it is the most expensive repair one can make to their car. To avoid further damage, enlist the help of a professional to replace your crankshaft. They have the training and experience to confirm the issue and the knowledge to complete the crankshaft replacement.

While engine services like this may be costly, it's a well-worth investment in avoiding further problems with your engine and saving your ride. The engine is a complicated system, and having a qualified technician is important to avoid any problems.

There are other issues that can bring about undesirable noises from your engine, but these 3 are the most typical issues that create a knocking sound.

How to Repair Engine Knock

We’ve said this multiple times throughout today’s blog, but we can’t stress it enough. To fix your car’s engine knock, it's best to have a professional mechanic diagnose the problem, determine the cause, and repair any issues with your engine before they lead to more serious problems. And, left alone, an engine knock will without a doubt lead to more serious problems.

Turn to Christian Brothers Automotive for Help with a Knocking Engine

If a persistent knock is interrupting your peaceful drive,Christian Brothers Automotive is here to help. Our friendly and professional expert technicians will thoroughlyinspect your engine and identify the source of the knocking sound. We’ll explain the cause, recommend a course of action, and work hard to get your car back on the road as quickly and safely as possible! Making sure your vehicle is getting you where you need to go is how we are Driving Joy. You have places to go, things to do, people to see!

Find your local CBA auto shop to claim yourCourtesy Inspection today!

This blog was written in May, 2013, and was updated in August, 2023, to reflect current industry standards and best practices.

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