We all use our car daily to get around town, whether to get to our jobs or go to our daughter’s friend’s birthday party.
But what happens when there’s trouble under the hood that needs mending?
Article summary
Uneven combustion of fuel air and fuel is the most common reason for an engine knocking sound when driving or idle. Many other things can also cause an engine knocking sound, including the following:
- Carbon accumulation in the combustion chamber
- Carbon accumulation on cylinder walls
- The quality of the fuel
- Bad timing of the sparks firing
- A leak in the vacuum
- Knock sensors deterioration
- Overheating of the engine
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It starts small. At first, it comes knocking on your hood and tries to tell you something is wrong. All you have to do in those moments is listen and repair.
8 Reasons a car engine has a knocking sound when driving & idle
We can solve all problems over time and with little extra care. Therefore, it is essential not to ignore them and hope they’ll go away independently. By the end of this article, I will cover all the causes so that you may understand them better and come up with a solution for all of your issues.
Let’s get started then and look at the reasons for a car engine knocking sound when driving & idle.
1. Ignition Knock
First of all, the most common engine knocking sound is the Ignition Knock. It’s the most important thing to understand the issue is to know its normal flow.
When the engine behaves normally, the fuel mixture that ignites burns in a single, administered explosion in each cylinder. The ignition Knock is the noise that will appear when the explosions happen multiple times in each cylinder.
Due to the fuel mixture and air intake in the engine can explode earlier than it’s supposed to. It causes a cascade effect of explosions that run into each other, causing the Ignition Knock.
If the car has a manufactured engine appraised for high-octane fuels, using low-octane rating fuel will damage all the parts. It causes buildup over time that leads to the slow deterioration of the engine and its slow demise.
Using a higher-octane fuel will benefit the explosions in the cylinders, leading to consistent burning of the air/fuel mixture.
Using a lower-octane fuel for a demanding car will entirely damage the components of your engine. It is ultimately the source of your engine knocking sound.
Always check the manufacturer’s manual to find the optimal octane rating designed for your car.
2. Timing Knock
Most of the newer brand cars have timing built into the motor’s computer. It determines the moment at which a spark should fire.
Unfortunately, the computer can cause the spark to ignite at the wrong time at any point due to technical errors. It leads to a multitude of explosions in the cylinder. You guessed it. It creates an engine knock.
3. Fuel/Air Mixture
Explosions happen in the cylinders through a perfectly calculated mixture of air and fuel injected into the chamber. It then creates synced chain explosions.
Any problem with your fuel injector/pump or any air sensors (oxygen sensor; airflow sensor) can create a surplus of the component needed for the explosion.
If there is a surplus of the mixture in the cylinder, the fuel existing will not have enough time to ignite fast enough. It leads to multiple detonations.
4. Malfunctioning Knock Sensor
Fortunately, manufacturers have already thought about the existing problems regarding engine knocking. Modern cars have a designed, built-in computer. It controls the air intake ratios, fuel injection, and the mixture’s timing.
A Knock Sensor is already built-in. It sends signals to the Engine Control Unit so that it can solve the problem on its own, without even beginning to notice the issue in the first place.
Having a malfunctioning Knock Sensor will allow the engine to knock. Checking the sensor first place is an essential part of troubleshooting and repairing.
5. Weary Bearings
Although it is not the most common, it is crucial for your motor system. For example, the rod knock is frequently miss-checked and poorly treated because of the repair cost involved once it occurs.
What is its meaning?
Its role is to transfer the power received from the motor to the wheels through the crankshaft’s support. The rod bearings can deteriorate over time by shifting position.
Because of its importance in transferring the power from pistons, the wearing will start to be noticed over time.
As they wear out, the pistons will begin to clatter against the crankshaft. In turn, it will cause the engine to knock.
6. Worn Belt Tensioner
Another typical knocking sound is a worn belt tensioner, although not so much in newer model cars. Although it is similar to engine knocking, it is not coming from the engine itself but the accessory belt.
Multiple tensioners on the accessory belt are constantly running attached to pulleys all over the engine bay. The moment the belt becomes out of synchronization and the tensioners extend, the pulleys become misshapen.
That is also when you hear sounds like the engine knocking, such as clattering, bangs, clangs, and jingles.
A simple replacement of the accessory belt or adjustments to the tensioners will eliminate the noisy sounds.
7. Poor Oil Quality
The most common issue when encountering knocking sounds is a poor oil quality choice. Although we invest a lot of money in other parts, not choosing a good quality oil or even premium can lead to the downfall of our engine.
Oil is integral to lubricating and cooling the operating engine components that play an essential role.
The camshaft, valve stems, and the gaps between the parts are all lubricated with oil. These components will manifest knocking sounds when those gaps enlarge and are tattered due to poor oil quality.
As we know it, the cold start makes the engine knocking sound most noticeable. When it starts, oil doesn’t have enough time to circulate through all components and gaps entirely.
High engine temperatures can also play an essential role in the slowly decaying oil quality, interfering with its development. Therefore, always use the car’s manufacturer’s recommended oil for your engine to avoid further lubrication problems.
Some other relevant causes:
8. Overheated Engine
An overheated engine traces back to cooling system problems. Take a quick look at your coolant levels and complete with the recommended quantities, if any are needed. A glance at your water pump could also do the trick.
Higher temperatures in the ignition chamber may cause pre-explosions. It results in knocking sounds since the fuel-air mixture ignites earlier.
10. Low engine revving
Knocking sound noticeable at low engine rev is often caused by a low octane level and stale fuel. It can be at revs at 1000-2000 RPM.
