Some words and concepts may seem a bit mysterious, until you experience them for yourself. 

Like the concept of engine knock. Drivers refer to it frequently, but what does it really mean? How will you know if you experience it? How concerned should you be? 

Let’s start at the beginning. 

What is engine knock? 

Engine knock, also known as detonation or spark knock, is a phenomenon that occurs within an internal combustion engine. 

Imagine the engine as a symphony of controlled explosions, where fuel and air mix in the combustion chamber to produce power. Now, imagine if this symphony were suddenly interrupted by an unruly drummer out of sync with the rest of the band – that’s engine knock.

When each engine cylinder has the correct balance of fuel and air, fuel burns in small controlled bursts and creates little shocks, igniting the next. If this doesn’t occur in rhythm, these bursts go off at the wrong time. The result? Engine knock. 

What engine knock feels like

As a driver, you can take two approaches to driving: reactive or proactive. A reactive driver ignores everything until you can’t ignore it anymore. A proactive driver pays attention to every detail, noting when your car isn’t driving the way it should. 

A proactive driver is more likely to notice the signs of engine knock. 

Engine knock is often first detected by the distinct sound it produces. It’s commonly described as a sharp, metallic “pinging” or “knocking” noise emanating from the engine bay. This noise may be more noticeable during acceleration or under load, such as when climbing hills or towing. In addition to audible cues, engine knock can manifest as vibrations or shakes felt through the steering wheel, floorboard, or even the entire vehicle. These vibrations are typically rhythmic and coincide with the detonation events happening within the engine.

Engine knock is often accompanied by a noticeable reduction in engine performance. You may experience a sluggish response to throttle inputs, a lack of power during acceleration, or a general feeling of the vehicle struggling to perform as expected. In severe cases, engine knock can produce unusual smells, such as the scent of burnt or overheated components. This may be an indication that the engine is working harder than usual, potentially causing increased wear and tear.

Modern vehicles are equipped with sophisticated onboard diagnostics; some may detect engine knock and trigger warning lights on the dashboard. If you see the “check engine” light or any other relevant warning lights, it’s essential to have your vehicle inspected promptly. Engine knock can contribute to increased temperatures within the engine. If you notice your temperature gauge rising more than usual, it could be a sign of detonation affecting the engine’s efficiency.

What causes engine knock?

Engine knock doesn’t happen out of the blue. Instead, it’s a slow decline caused by wear and tear. Every time you start the car, it impacts performance. Every road you move down affects the car in some way. 

Incorrect Fuel Octane Rating

One of the primary causes of engine knock is using fuel with an octane rating lower than your engine requires. Octane rating indicates a fuel’s resistance to premature ignition. High-performance or turbocharged engines often demand higher octane fuel to prevent knock.

Advanced Ignition Timing

Ignition timing refers to the precise moment the spark plug ignites the air-fuel mixture. If the ignition timing is too advanced, meaning the spark occurs too early, it can increase pressure and temperature in the combustion chamber, causing knocking.

Excessive Engine Temperature

Overheating can be a catalyst for engine knock. High temperatures contribute to the formation of hotspots in the combustion chamber, promoting spontaneous ignition of the fuel-air mixture before the spark plug fires.

Carbon Deposits

Carbon deposits on the combustion chamber walls can act as hot spots, initiating combustion before the spark plug ignites. This is more common in engines with poor fuel quality or prolonged use of low-quality oils.

How engine knock affects a car over time

What’s that sound? Ignoring or neglecting the signs of engine knock can lead to progressively severe consequences. If you ignore the sound coming from your engine, the effects can be severe:

Piston and Cylinder Damage

Engine knock creates intense pressure waves within the combustion chamber, leading to forceful impacts on the piston and cylinder walls. Over time, these repeated impacts can cause accelerated wear and damage to these critical components.

Connecting Rod Wear

The connecting rods, which link the pistons to the crankshaft, are also vulnerable to the effects of engine knock. The forceful detonations can lead to increased stress on the connecting rods, potentially resulting in bending or other forms of damage.

Spark Plug and Ignition System Issues

Persistent engine knock can negatively impact the spark plugs and the entire ignition system. The excessive pressure and heat generated during detonation can cause premature wear on spark plug electrodes, leading to misfires and a further deterioration of engine performance.

Increased Heat and Friction

Engine knock contributes to higher temperatures within the combustion chamber. The increased heat, combined with friction from the forceful detonations, accelerates overall wear on engine components. This can lead to a reduction in engine efficiency and an increased likelihood of component failure.

Reduced Fuel Efficiency

As engine knock compromises the efficient combustion of fuel and air, the engine has to work harder to maintain performance. This increased workload results in higher fuel consumption, leading to reduced overall fuel efficiency.

Catalytic Converter Damage

The heightened temperatures caused by engine knock can harm the catalytic converter. Over time, this may lead to a decline in efficiency and functionality, potentially triggering the illumination of the “check engine” light and necessitating costly repairs.

Engine Knock Feedback Loop

If left unaddressed, engine knock can create a feedback loop of damage. For example, damaged pistons and cylinders can lead to irregular combustion, further exacerbating engine knock and accelerating the wear and tear on various components.

Costly Repairs

The cumulative effects of engine knock can result in substantial and expensive repairs. Rebuilding or replacing damaged engine components, such as pistons, connecting rods, or the entire engine block, can be a significant financial burden.

What’s coming from underneath your hood?

Being a proactive driver means paying attention to every little detail. When something sounds off, it probably is. 

That’s when it’s time to bring your vehicle in for an inspection. That’s when we can discover what’s wrong before it becomes a more serious issue. 

How can we help you today?