Knocks and noise in the engine – is it the reason to worry?

Before we begin, someone might tell you that if you hear a knock in your engine, it’s nothing serious—perhaps it’s “just how the engine is built.” But let’s be clear: what does a knock in the engine mean? Continues engine knocking is not normal, and ignoring it could result in significant damage and costly repairs. This article is especially helpful for beginner drivers who may be unsure whether to panic or keep driving.

What does a knocking engine sound like?

It can be particularly difficult for new drivers to identify the complexity of the engine detonation problem by sound. Engine knocking is a series of metallic, rhythmic tapping, pinging noises that typically occurs at the same pace as the engine RPM; as the engine spins faster and faster, the knock becomes quicker and louder.

You may first notice a tapping noise when starting a car, particularly after it’s been parked for a few hours at low temperatures. As the engine heats up, the noise may seem to diminish -  and it is normal. But if you notice that it continues or not stopping and becomes worse, it is a signal for a car check up.

So, the knocking sound might occur when your car is under load, such as when you are accelerating or ascending a hill. Under these conditions, such noises are unnatural sounds for an engine. 

Common engine noises that can mislead drivers

Some noises may sound alarming, but are not always dangerous:

• Absorber valve knock

This valve, which is found mainly in older cars, returns fuel vapours to the system. Knocking is rare and is not a critical problem.

• Fuel injector ticks

This can sound like a knock but is often due to the internal spring mechanism. If the sound is annoying, replacing the injectors may solve it.

• Pushrods and hydraulic lifters

If you hear a knock only when the engine is cold, worn pushrods or lifters could be the cause. As the engine warms, the noise often disappears.

• VVEL chain noise

It is quite a significant problem.  If the belt is installed, then nothing will knock, but if the chain is responsible for the functioning of the Variable Valve Event and Lift system, it may produce knocking when it is worn. Replace VVEL details to avoid costly repairs.

What causes a knocking sound in the engine?

There are several potential reasons:

❖ When the fuel ignites unevenly or too early, it can cause engine knock. It is a sharp, loud knocking sound that can damage the pistons.
❖ Worn phase inverter – Typically knocks under load (around 900–2000 RPM). A failing phase inverter may also produce a whistling sound.
❖ Piston slap – Worn pistons can rock inside the cylinder, hitting the walls. Over time, this causes additional engine damage.
❖ Crankshaft knock – The most serious type. It can be caused by worn or failed rod bearings. Eventually, this could lead to complete engine failure.

What does engine knocking at idle and accelerating indicate?

Engine knocking at idle and accelerating is a classic red flag. It often points to issues with the crankshaft, rod bearings, or timing components. If left unchecked, the engine could seize. Always address persistent knocking quickly.

Can you fix a knocking engine? It depends on the cause. Minor knocking from injectors or a worn lifter might be inexpensive to fix. However, crankshaft-related knocking may require a full engine rebuild or replacement. The earlier you catch it, the better.

Can an oil change stop engine knocking? Yes—if the knocking is caused by low oil levels or degraded oil that has lost its viscosity. Fresh oil can improve lubrication and silence minor hydraulic lifter noise. But for mechanical wear or damage, an oil change won’t help.

Can you drive with a knocking engine? Technically, you can. But diagnose the engine as soon as possible. Driving with a knocking engine may cause catastrophic damage. Check your car with the OBD2 inCarDoc app and apply to a service station for detailed investigation. 

How to protect your engine from knocking

Preventing engine knock is far easier—and significantly cheaper—than repairing the damage it can cause. Here are several proven strategies to help you protect your engine from knocking and avoid costly repairs:

• Use high-quality fuel with the correct octane rating. Always use the fuel recommended by your vehicle’s manufacturer. Using a lower grade can lead to premature combustion, also known as detonation, which creates knocking and can severely damage pistons and valves.

• Perform regular oil changes using the manufacturer-recommended oil type. Engine oil lubricates moving parts and helps dissipate heat.Timely oil changes are essential to avoid increased friction, heat buildup, and eventually knocking sounds.

• Avoid engine overheating by monitoring coolant levels and checking the condition of the radiator. You can use inCarDoc to record real-time engine parameters. 

• Clean or replace fuel injectors on a routine basis. Dirty or clogged injectors can cause an uneven air-fuel mixture, leading to poor combustion and knocking.

• Inspect and replace timing components based on mileage and wear. When these parts wear out or stretch, it can cause valves to open or close at the wrong time, potentially resulting in knocking or catastrophic internal damage.

• Use vehicle diagnostic tools like inCarDoc. Modern apps such as inCarDoc allow you to connect to your car’s OBD2 system via smartphone and monitor engine performance in real-time. These tools can help detect early signs of engine trouble, including knocking, long before they escalate into expensive failures. They are a practical, affordable way to stay in control of your engine’s health.

Thorough car inspection as a solution against knocks

Recognizing the warning signs of engine knocking and responding promptly can prevent minor issues from turning into major repairs. From subtle ticking to loud knocking, every unusual engine sound deserves attention. Don’t wait for a breakdown — listen to your car, identify the cause, and act early to keep your engine running smoothly and reliably