If you hear knocking sounds from your engine, it could be due to high compression, uneven fuel ignition, or faults with engine components. To prevent knocking, use higher-quality oil and ensure you’re using the right octane fuel.
Using low-quality fuel with an inadequate octane rating or carbon deposits in the combustion chamber can also cause knocking. Low oil levels and dirty oil can contribute to engine knocking as well.
That way, you need to know more about the engine knocking and what to do about the faulty signs. Well, in this reading, we’ll explore about engine knock, why an engine knocks, and what a knocking engine sounds like.
Let’s begin!
What is Engine Knock?
Engine knock typically happens when the air-fuel mixture in the cylinders fails to ignite in a controlled manner or when metal components collide that shouldn’t.
When cylinders have the proper air-fuel balance, fuel burns in discrete, regulated pockets rather than all at once. Think sparklers rather than fireworks.
After each pocket burns, it produces a little shock, which ignites the next pocket and continues the cycle. Engine banging occurs when the fuel burns unevenly and the shocks activate at the wrong time.
The end results? An obnoxious noise and the possibility of cylinder wall and piston damage in your engine.
In a properly functioning engine, air and fuel (usually gasoline) are mixed, compressed, and ignited by a spark plug. This controlled combustion creates an explosion that pushes the pistons down, generating power to drive the engine.
This cycle repeats continuously to keep the vehicle moving.
If you hear knocking during acceleration or while driving, it’s likely due to combustion occurring at the wrong time.
Related: Engine Overheating: Causes, Symptoms, and Solution
Sound of Engine Knocking
Engine knock is a tapping, pinging sound that increases in volume and annoyance as you accelerate. When fuel burns unevenly in your engine’s cylinders, it causes knocking.
Engine knock isn’t always an obvious, loud knocking or thunking noise while driving. It can be quite subtle, and if you often drive with your music turned up high, you might not notice it at all!
The sound of engine knock can range from a metallic pinging to a repetitive tapping or a metal-on-metal plinking noise. Its volume, frequency, and timing can vary depending on the cause and severity. However, it’s most commonly noticeable during acceleration.
Causes of an Engine Knocking
The most common reason reason why an engine knock is:
- A faulty or improper spark plug
- Low-quality or low-octane fuel
- Wrong ignition timing
- Mixture of Lean Airfuel
- Crankshaft Damaged or Broken
- Serpentine Belt Extending
- Bearings that have worn out
- A faulty knock sensor
- Non-Lubricated Cylinder Head
- Valve lifter failure
- Low Oil Pressure
1. A Faulty or Improper Spark Plug
Spark plugs are in charge of producing the spark in your engine’s combustion chamber. This spark ignites the air-fuel mixture, resulting in engine power.
Premature detonation within the combustion chamber may occur if your engine has a faulty spark plug or spark plugs that do not meet the criteria of the specific engine. This can result in a detonation knock on the engine.
2. Low-Quality or Low-Octane Fuel
Every fuel type is assigned a number based on its octane rating. The higher the octane rating, the more refined the fuel. In other words, the higher the amount of octane, the more regulated the detonation of air fuel.
When you put low-octane gasoline in your car, it might cause the airfuel mixture to burst prematurely, resulting in an engine knocking sound.
3. Mixture of Lean Airfuel
To continue with the combustion concept, the “spark” supplied by the spark plugs ignites a compressed air-fuel mixture. Multiple detonations and a loud knocking engine noise occur when there is a low proportion of fuel in this mixture.
Check and inspects the engine components that control the flow of air and fuel within the engine, such as the fuel injectors and mass airflow sensors, as these have an impact on your air-fuel ratio.
4. Carbon Deposits
In order to prevent carbon deposits from clogging your cylinders, every fuel sold in the United States must contain carbon-cleaning chemicals. Unfortunately, some deposits remain.
When this occurs, there is less space for the fuel and air to reside, resulting in higher compression. Changes in fuel compression, as you know with fuel, can cause unpleasant knocking sounds.
Crankshaft Damaged or Broken
Inside the cylinders attached to the crankshaft, the piston rings of your car’s engine travel up and down. The engine timing system controls this. The rods and bearings that connect the cylinders to the crankshaft are critical for maintaining optimum cylinder-to-crankshaft clearance.
When the crankshaft is damaged and the clearance between the cylinders is not properly maintained, metal-on-metal contact can occur, resulting in a rod knock.
5. Wrong Ignition Timing
When the ignition timing is too advanced, the engine will begin to knock or ping. As a result, wrong ignition timing could result in an engine knock. This only applies if your car has adjustable ignition timing on the distributor or an adjustable cam or crankshaft position sensor.
Unfortunately, because contemporary cars manage the ignition timing entirely electronically, manual adjustment is not possible.
6. Serpentine Belt Extending
When a car’s engine runs, it rotates a serpentine belt that connects to multiple pulleys (which power various accessories) around the engine bay. This belt must have precisely the correct amount of tension to spin silently and smoothly.
An overly stretched belt will be unable to maintain the proper degree of tension, resulting in rattling, clicking, or screaming noises that can be confused with normal engine noise.
7. Bearings that have worn out
As your car ages and the engine wears out, the connecting rod bearings between the cylinders and the crankshaft may begin to fail, leading to a rough ride and a loud rod knock.
Particles accumulate in the engine as cars age, and combustion by-products such as carbon deposits, dirt, and grime can collect at the back of the rod bearing.
8. A Faulty Knock Sensor
Most modern vehicles include a knock sensor, which detects engine banging and delivers data to the Engine Control Unit (ECU). The ECU then automatically corrects the problem.
If your knock sensor is damaged or broken, the engine will continue to knock. A faulty knock sensor will also illuminate the check engine light.
9. Non-Lubricated Cylinder Head
Lubrication is required for all engine cylinders. Unlubricated cylinders make a knocking sound. When there is an engine oil leak, a cylinder will normally lose lubrication.
Using generic oils with lower flashpoints might also result in poor engine lubrication. As a result, several automakers advise using synthetic engine oil to lubricate the cylinder head.
10. Valve Lifter Failure
A valve lifter is a crucial engine component responsible for transferring motion to open and close the valves. If your oil hasn’t been changed in a while, dirt and debris can build up in the lifters, causing a persistent knocking noise when you start the engine.
Additionally, using the wrong grade of oil can clog the lifters and lead to similar issues.
Fortunately, changing the oil and running a cleaning agent through the engine may resolve the knocking sound. Refer to your vehicle’s handbook for guidance on the recommended oil change intervals and the appropriate type of oil for your engine.
11. Low Oil Pressure
Engine oil is a critical lubricant that ensures your motor operates smoothly. Without it, the engine can seize, and its internal components may collide, causing a knocking sound and potentially leading to severe long-term damage.
Low oil pressure might also indicate a leak. Check your oil level and top it up if needed. If the level drops again quickly, it’s a sign of a leak in the system, and you should contact a mechanic to arrange repairs.
When the oil level is too low, the oil pump can draw in air instead of oil. Air doesn’t provide the necessary lubrication, leaving engine components unprotected. This lack of lubrication can cause the bearings to overheat due to friction, leading to knocking and even melting.
How to Fix Engine Knocking?
Below is how you can fix an engine knocking:
1. Change Oil and Filter
The first step is to perform an oil change. Oil lubricates the engine’s moving parts, dissipates heat, and removes metal particles and debris. While the oil filter captures most contaminants, sludge can still accumulate and circulate back into the engine.
Old or dirty oil can cause components to stick, while unsuitable oil may thin under heat, leaving a sticky residue on cylinder walls and damaging other parts. Replace the oil and filter with the type recommended by the manufacturer every 5,000 to 8,000 miles.
While the older standard was every 3,000 miles or 3–6 months, some extend it to 10,000 miles—but that may be risky.
2. Use High-Octane Fuel
Fuel quality directly affects engine performance and longevity. Although low-octane fuel is cheaper, it can reduce engine efficiency and may lead to expensive repairs.
If you notice engine knock, ensure you’re using the fuel type specified by the manufacturer. You can also add an octane booster to increase fuel quality and reduce knocking.
3. Add Fuel Detergent
Most fuels already include detergent to prevent carbon buildup on cylinder walls and spark plugs. However, carbon deposits can still cause hot spots, premature detonation, and knocking noises. Using a supplemental fuel cleaner can help remove deposits and reduce engine knock.
4. Clean the Combustion Chamber
Carbon deposits in the combustion chamber can decrease its volume, raise compression, and disrupt the combustion process, leading to reduced efficiency and power.
To clean the combustion chamber, use specialized cleaning products and follow the instructions carefully. You can also watch online tutorials or consult a trusted mechanic for professional cleaning.
5. Check or Replace Spark Plugs
Spark plugs must be properly gapped and designed for the correct heat range. Faulty or improperly gapped spark plugs can cause spark knock and premature knocking.
Carbon buildup on the electrodes can also narrow the gap, affecting ignition. Regularly check and clean your spark plugs, and ensure they meet your vehicle’s specifications. Replace them if necessary, and adjust the gap to the manufacturer’s recommendations.
6. Reduce Intake Charge Density/Temperature
Cooler air is denser and expands more during combustion, providing better oxygen for the air-fuel mixture. Lowering the intake air temperature improves combustion efficiency and reduces the chance of knocking.
Ensure the air intake is free of dirt and positioned away from hot engine components like the exhaust manifold to allow cooler air to enter.
7. Increase Engine Speed
Short, low-speed trips can prevent the engine from reaching optimal temperature, leading to carbon buildup. Additionally, low RPM knocking can result from stale or low-octane fuel left in the engine for extended periods.
Use the recommended fuel grade and periodically take your car on a highway drive for about an hour to help clean out the system.
8. Replace the Knock Sensor
Engine knocking could indicate a faulty knock sensor. Since this sensor is located in a less accessible area and requires specialized tools for testing, it’s best to have it checked by a trusted mechanic. Replace it if necessary to restore proper engine function.
9. Adjust the Air-Fuel Mixture
The air-fuel mixture plays a critical role in combustion. A richer mixture (more fuel) lowers compression temperature, reducing the risk of premature detonation.
At higher altitudes, where the air is thinner, a leaner mixture (less fuel) can ensure more complete combustion and minimize the chance of detonation knock. Adjusting the mixture to suit your driving conditions can help optimize engine performance and reduce knocking.
What Should I Do If My Car Engine Is Knocking?
You’re undoubtedly curious about how to remedy the engine knock now that you’re aware of the various causes. The first thing you must consider is when the knocking occurs.
If it happened after you refueled the car, you most likely have contaminated fuel in the tank. To correct this, either replenish the fuel or try using an octane booster.
You should examine and change the ignition timing if you have an older car or if the engine has adjustable ignition timing. Check your service manual to see if you have adjustable timing.
If you are unfamiliar with altering timing, have a repair company handle it because the technique requires certain special gear. However, the best course of action is to have your car checked by a specialist for thorough diagnosis and repairs.
Is It Recommended To Drive If You Hear an Engine Knocking?
A knocking sound is frequently the result of an issue with an engine’s internal components. It is not recommended to drive if you hear a knocking noise.
The greater the engine damage to these core components, the more complex and expensive the repair process. It’s possible that you’ll need to repair expensive engine parts.
What Is the Cost to Repair Engine Knocking?
Hearing engine knocking can be unsettling—and for good reason. Strange noises coming from your engine are rarely a good sign and often point to potential costly repairs that can strain your budget.
However, engine knocking doesn’t always mean the worst. In some cases, replacing your car’s spark plugs can resolve the issue. This repair typically costs a few hundred dollars and won’t leave you without your vehicle for long.
That said, ignoring engine knock for too long can lead to more serious problems. Over time, the issue could escalate and result in worn-out engine bearings, which may cost you several thousand dollars to fix. Addressing the problem early can save you significant time, money, and stress.
Related: What Is An Engine Lubrication System? Its Functions And Parts
FAQs
What causes engine knocking?
Engine knocking, also known as detonation, is typically caused by the premature ignition of the air-fuel mixture in the engine cylinder. It occurs when the compressed air-fuel mixture ignites before the spark plug fires, leading to multiple flame fronts colliding and producing a knocking sound.
How do you fix a knocking engine?
Fixing a knocking engine depends on the underlying cause. It could involve using higher octane fuel, addressing ignition timing issues, replacing faulty spark plugs, ensuring proper engine cooling, or repairing damaged engine components. In severe cases, a mechanic may need to inspect the engine for more significant issues.
What is knocking in a petrol engine?
Knocking-in a petrol engine refers to the rattling or metallic sound produced when the air-fuel mixture combusts at the wrong time due to factors like low-quality fuel, excessive engine load, or improper ignition timing.
What does a knocking sound in the engine mean?
A knocking sound in the engine indicates the occurrence of detonation or pre-ignition, where the air-fuel mixture ignites spontaneously and not as intended. This knocking noise is a sign of potential issues that require attention to prevent engine damage.
Can knocking damage an engine?
Yes, knocking can damage an engine over time if left unaddressed. The repeated knocking events put extra stress on engine components, leading to increased wear and potential damage to the pistons, cylinder walls, bearings, and other vital engine parts.
Can a knocking engine be saved?
The ability to save a knocking engine depends on the severity of the problem and how quickly it is addressed. In some cases, simple fixes like using the correct fuel or adjusting the ignition timing can resolve the issue. However, if the knocking is due to significant internal damage, it may require extensive repairs or even an engine replacement.
Can too much oil cause knock?
Yes, too much oil in the engine can cause knocking. When there’s an excessive amount of oil, it can create excessive pressure on the crankshaft and connecting rod bearings, leading to engine knocking.
Can spark plugs cause engine knock?
Yes, faulty or incorrect spark plugs can cause an engine knock. If the spark plugs are not functioning correctly, they may ignite the air-fuel mixture at the wrong time, contributing to engine knocking.
Do I need a new engine if it’s knocking?
Not necessarily. Whether you need a new engine depends on the severity of the knocking and the extent of the damage. In some cases, engine knocking can be resolved with repairs or adjustments. However, if the damage is significant and beyond repair, a new engine may be necessary.