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Causes of Knocking Noise in a Car Engine

Causes of Knocking Noise in a Car Engine

What is engine knocking? What do these symptoms point towards? These are the questions that are dealt with, in this article. Read to know about the prime causes of this phenomenon.
Omkar Phatak
One of the most alarming of car problems, which should not be ignored, is engine knocking. Needless to say, the most important car part is the engine and a breakdown there, can result into a complete failure of car functioning and costly repairs.

A bike or a car talks to you, through all the sounds and noise it makes. Experienced mechanics can even tell what's wrong with the car, by listening to how it sounds. So, you need to learn to understand the normal sounds made by the car and which ones indicate trouble. Remember that a loud knocking sound in engine or transmission, definitely means trouble.


The loud knocking noise presents itself, when you hit the gas pedal and throttle injects more air to the engine. Normally, this noise may be a high pitched resonant sound and sometimes, even a kind of rattle, which can be extremely irritating. In any case, it is not good news and there are a number of reasons why this might be happening. Here are the prime causes.

Engine Overheating
One of the prime reasons is engine overheating due to improper action of the cooling system. An engine coolant leak might cause the overheating, which can lead to a knocking noise, due to pre-ignition. This phenomenon causes the fuel in your engine to spontaneously explode in the high temperature environment. This problem can be prevented by regularly checking out the engine coolant levels and ensuring that the system is working properly.

Engine Cycle Timing Problems
The engine cycle's rhythm can get disturbed if the spark plug firing and the fuel mixture combustion, are not synchronized. In the event that spark plug timing and combustion don't match, there is bound to be a knocking noise. This problem can only be dealt with, by a repair center.

Mechanical Alignment Problems
One of the prime reasons is misalignment of some of the engine components. This includes, more than normal clearance in the crankshaft connecting rod bearings or it may be due to entirely defective crankshaft bearings. If this is actually the case, you can expect quite a loud noise, as metal hits metal surface, creating a ruckus. In this event too, you need to get to the car repair center, as soon as possible.

Lean Air-fuel Mixture
Sometimes, the noise can be attributed to too lean an air-fuel mixture, in the combustion chamber. This condition of lesser fuel, with more oxygen availability, may lead to pre-ignition and to the knocking noise ultimately. You need to get the engine tuned properly, to prevent this from happening. One of the best ways to prevent this situation, is to go for regular engine servicing.

EGR Valve Problems
If the exhaust gas recirculation (EGR) valve mechanism is messed up, it may result into the noise, due to an abnormal change in the air-fuel mixture ratio. Valve cleaning and repair might solve the problem quite easily.

It is highly advisable that you get your car to the servicing center, as soon as possible, if loud knocking noises present themselves. This will save you a lot of time and money, spent in repairs later.