Why Is the Engine Knocking When Accelerating (Causes & Fixes)

One day, when I was driving my car, I noticed an incredibly loud and persistent engine knocking sound when I was accelerating. Assuming that it was just a fluke,  I carried on driving, but the noise kept getting worse so I decided to take my car to the nearest mechanic for an assessment.

The mechanic told me that it was due to a low oil level. There are other reasons for the engine to be knocking when accelerating as well, such as having a bad knock sensor, a low octane level, bad spark plugs, improper fuel-to-air mixture, or when there are an excessive amount of carbon deposits in the combustion chambers.

I found out that a low oil level is the most likely reason for the engine to be knocking when accelerating. There are other things that I’ll be talking about below as well, so if you’d like to learn more about all the reasons why your engine is knocking when accelerating, keep on reading.

What Does a Knocking Engine Sound Like?

A knocking engine sounds like a drumming or tapping noise that typically comes from the engine’s cylinders. It is caused by pre-ignition, detonation, or pinging, which occurs when fuel combusts before the spark plug fires it off during the normal combustion cycle within an internal combustion engine.

The result can be loud knocking sounds that vary in intensity depending on various factors such as the octane rating of gasoline used, and the type and quality of spark plug installed.

Typically it will be noticed at idle speed first where little vibrations come through the hood to indicate there’s something wrong with your vehicle’s motor. It will be more than just the regular operational noise you’re used to hearing while driving around town.

In some cases, this may also coincide with performance issues, such as stuttering acceleration, but usually only when specifically revved up under load conditions since internal pressures become greater causing an unburnt mix of air/fuel mixture to ignite prematurely, and hence producing a noticeable pounding onto pistons moving inside cylinders.

It ultimately leads to the engine rattling multiple times per second and sometimes it will even be audible outside. You might be wondering if it’s even safe to drive when you have a knocking engine.

What Causes Engine Knock When Accelerating?

Low Oil Level

The engine knocking sound when accelerating can be caused by a low oil level. This can happen for several reasons, but the most common is simply forgetting to check or top off the oil regularly.

A car’s engine needs a constant supply of fresh, clean oil to lubricate all of its moving parts and keep them running smoothly together. if there isn’t enough oil, or if the oil becomes old and dirty, it will no longer be able to do its job properly.

The result will be increased friction between the engine’s components, which leads to that characteristic knocking noise, and eventually serious damage to your engine if left unchecked. If you check your oil level and it’s not low, then there could be a problem with the knock sensor.

Can Thin Oil Cause Knocking?

Yes, thin oil can cause knocking. When oil is too thin, it doesn’t provide enough cushioning between the pistons and cylinder walls. This can lead to metal-on-metal contact, which causes a knocking noise to emanate from the engine.

If left unchecked, this can eventually damage the engine. Knocking happens when the air/fuel mixture in the cylinders ignites too early. This thin oil will not be able to provide adequate lubrication for your engine components, which will lead to premature wear and tear.

Will an Oil Change Stop Engine From Knocking?

In some cases, an oil change can help stop the knocking and allow your engine to run smoothly again. If your engine is low on oil, it can cause the parts to rub against each other and make a knocking noise.

Therefore, adding more oil can help lubricate the moving parts and reduce the friction between them, and thus in turn stop the engine from knocking. But before you make an oil change, you might want to check whether the oil you’re using is too thin or not.

Bad Knock Sensor

If your car’s engine is knocking when accelerating, it could be caused by a bad knock sensor. The knock sensor is designed to detect knocking and adjust the ignition timing accordingly. If the knock sensor isn’t working properly, the ignition timing will be off and cause the engine to knock.

In some cases, a bad knock sensor can also cause the engine to run lean, which can damage the engine beyond repair. If you check your car’s knock sensor, and there’s nothing wrong with it, then there could be an issue with your car’s octane fuel.

Low Octane Fuel

When the octane is too low, it can cause your car’s engine to knock when accelerating.

An octane rating, or octane number, is a standard measure of the performance of the engine’s gasoline. It is measured in terms of how much compression the fuel can withstand before detonating.

Knocking occurs when pockets of air/fuel mixture ignite too early inside the cylinder as it approaches the top dead center on its combustion stroke. When these mini fireballs collide they create a knocking noise and this causes premature wear on pistons and rings from repeating shock waves going through them as well as robbing power from the explosion itself.

Fuel with a higher octane number will resist “knocking” or “pinging” during combustion, while lower-octane fuels will cause these events to occur more frequently.

In broad terms, fuels with an octane rating below 91 are referred to as regular unleaded gasoline, while those above 91 are called premium unleaded gasoline. If you’ve checked your octane level and it’s not too low, then there could be a problem with your spark plugs.

Spark Plugs

If your car engine is knocking when you accelerate, it could be a sign that your spark plugs need to be replaced. Spark plugs are one of the most important components of your car’s engine, and they can cause all sorts of problems if they’re not working properly.

Bad spark plugs can cause engine knock, which is a knocking or pinging sound that occurs when the air/fuel mixture in the cylinders isn’t detonating correctly. This can lead to decreased performance and fuel economy as well as increased emissions.

If you think your spark plugs may be causing the engine to knock, it’s best to take them to a mechanic for diagnosis and see if they’re causing the problem. If there are no issues with the spark plugs in your car, then there could be a problem with the fuel and air mixture in your vehicle.

Improper Fuel/Air Mixture

If your engine is knocking or shaking when you accelerate, it’s likely due to an improper fuel/air mixture.

Running too lean, or in other words, not having enough fuel, will cause the air-fuel mixture to detonate prematurely in the cylinders. This can happen if the carburetor isn’t adjusted properly, or if there’s a problem with the ignition timing.

This “knocking” noise is mini explosions happening inside your engine. Running too rich, or in other words, too much fuel, can also cause knocking, but for different reasons.

When an engine runs too rich, unburned fuel can build up on the piston heads and ignite all at once when hot exhaust gasses hit it during compression strokes.

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Either way, this cylinder distortion from premature detonation puts tremendous stress on connecting rods and crankshafts which leads to the engine knocking. If you check the fuel and air mixture, and there’s no issue with it, then there could be a problem with the carbon deposits.

Excessive Carbon Deposits

An excessive amount of carbon deposits can cause the engine to knock when accelerating. These deposits build up on the intake valves and combustion chambers, causing the engine to run less efficiently over time.

Carbon buildup is more common in today’s engines because they are designed to run cleaner than older models.

This means that there’s less opportunity for these deposits to be burned off during normal operation.

Over time, they will accumulate and eventually cause problems like knocking or misfiring. The best way to avoid this issue is to simply remove the excessive carbon deposits when they come up, according to the manufacturer’s recommendations.

If you checked your carbon deposit buildups and there are none, but the engine is still knocking when accelerating, you will require some more specific instructions on how to fix the issue.

Is It Safe To Drive With a Knocking Engine?

While it’s normally safe to drive for a short distance with a knocking engine, continuing to do so wouldn’t be safe, and doing so could cause some damage to your engine. The problem will only get worse over time and can eventually lead to engine failure.

Continuing to drive with a knocking engine will only end up costing you a lot of money in repairs down the road. You might be curious about exactly how much money you will need to spend on repairs if your car happens to have a knocking engine.

How To Fix Engine Knocking

1. Check the oil level and make sure it is full.

If the oil level is low, replenish it for around $20 to $60 and see if the knocking goes away. If your engine oil level is too low, it can cause the engine to knock. The knocking sound is caused by the pistons hitting the cylinder walls. This can damage the engine and cause expensive repairs.

2. Check to see if your knock sensor is working properly.

This small sensor is designed to detect when the air/fuel mixture in the cylinders is detonating too early. When this happens, it sends a signal to the computer which then delays the ignition timing to help prevent engine damage. If the knock sensor fails, you will have to have it replaced by a mechanic, costing you around $300 to $400.

3. Check the fuel’s octane level in your vehicle.

When your fuel has a low octane level it can cause the engine to knock, because the lower octane level means that the fuel ignites too early. This can cause damage to your engine and decrease its efficiency. To fix this problem, you will have to increase the fuel’s octane level.

4. Inspect the spark plugs in your vehicle.

You will have to replace them if they’re not working properly, since worn-out or damaged spark plugs can allow oil and other contaminants to enter the combustion chamber, therefore leading to the engine knocking. Replacing the spark plugs with a mechanic will normally cost you around $200 to $250.

5. Finally, Test out the combustion chamber

if there are an excessive amount of carbon deposits inside of it, you should clean it out. Carbon deposits usually build up inside the combustion chamber over time due to an abundance of unburned carbon stranded in there. You will need both a brush and solvents to clean out the combustion chamber properly.

If you’ve completed all of the steps above, then your engine should now no longer be knocking.

How Much Does It Cost To Fix a Knocking Engine?

The cost of repairs will depend on the severity of the issue and the make and model of your vehicle, but on average it will cost around $2000 to $3000 to fix your car when it has a knocking engine.

That includes both the cost of the parts and the cost of hiring the mechanic to fix the problem. But before you take your car to a qualified mechanic to get it fixed, you might want to first try changing the oil first, as that could help you fix the issue.