Updated at: 03-08-2023 - By: Lucas

The smooth, accurate, and practically silent operation of a car’s engine is a sign that it is working well. Even when the engine is cool, certain noises might be alarming because they are an indication that something is wrong and has to be fixed right away.

When the engine is cold, a knock might be heard.

The engine may be knocking for a variety of reasons. The majority of knocks are the result of relatively small issues that are quickly identified and remedied. The internal combustion engine is a complex machine, and various noises can indicate that something is wrong with it and necessitate rapid attention.

Types of engine knockings

Engine Knock When Cold

Internal combustion engines produce a wide variety of sounds due of the collisions between various components, each of which produces a distinct sound.

  • If the engine noise is weak, perhaps disappearing when driving, the car is usually not in danger of serious damage, but checking the engine timely is always a good idea even if there is no knocking 
  • The average volume and intensity of the sound indicate more serious problems. In this case, the first thing you need to do is to go to the nearest workshop to avoid serious engine problems.
  • If the sound is clear and loud, then the driver should urgently turn off the engine and call a tow truck. If you continue to drive like this the engine may stall.

What are the causes of engine knocks?

Engine Knock When Cold-2

Knocks in the engine can occur for a variety of causes. In particular, mechanical wear of components and assemblies and the development of detonation processes are to blame. It is the failure of a portion or the degree of explosion that determines the sound’s character. For a proper diagnosis, this element is essential.

When starting a cold internal combustion engine, you may hear a knocking sound. As the engine warms up, the knocking sound may become less strong, or it may even become louder due to increased pressure and/or temperature.

As a result, the most common causes of engine knock include

  • Metal knocking in the engine provided that the internal combustion engine is fully serviceable, signals that the accepted norms of thermal gaps do not meet. You can correct this situation by adjusting the valves professionally.
  • The loss of performance of hydraulic compensators also causes the engine to knock when cold. Compensators fail, due to mechanical wear, the use of oil that is unsuitable for the car according to the required specifications, as well as its untimely replacement. To eliminate this problem, it is enough to perform a complete engine wash, replace the engine oil with a required one, and oil filter as well.
  • Increasing the gap between the main bearings may cause knocking in the first few seconds after starting the engine. It is self-canceling when the pressure indicator of the lubrication system increases. Incorrect operation of the bearings can also be caused by a decrease in the performance of the oil pump.

In this case, the amount of incoming oil becomes insufficient, and at the same time, there is a blockage of the channels, which leads to the fact that the oil does not have time to produce high-quality lubrication of all components and parts. As a result, they begin to emit an unpleasant rattle and rasp.

  • Dull metal repeated blows in the engine when accelerating may indicate a failure in the connecting rods. This sound is characteristic of a worn connecting rod hitting the crankshaft neck. Here you need the urgent help of a professional car mechanic, as the operation of the car in this condition is strictly prohibited.
  • The characteristic sound in the engine also indicates that there are problems with the gas distribution mechanism. The most common reason is an increase in camshaft clearances. When the engine is subsequently warmed up, these knocks become either less intense or completely disappear.
  • If the piston is sufficiently worn, it can also make a tapping sound during operation. Damaged pistons move freely, as if “walking” in the cylinders, causing a characteristic metallic sound when the “skirt” hits. Similar knocking can cause the deformation of the piston rings.
  • The knock caused by the detonation is quite loud. Its intensity naturally increases with each engine cycle. The main reason is the untimely and uneven ignition of the fuel-air mixture, which provokes spontaneous destructive explosions inside the cylinders.
  • When the engine is cold, the appearance of detonation shocks, and hence the characteristic knock results in the use of fuel with lower octane (according to the manufacturer’s recommendations).
  • A very common factor in the appearance of engine knocking is the use of a thinner cylinder head gasket, which causes an increase in the compression ratio.
  • Various knocks in the under-hood area can be caused by various breakdowns of attachments and units, such as the water pump generator, timing, etc.

How to diagnose engine knocks yourself

Try to figure out why the engine’s distinctive metallic sound started if you can’t get a professional diagnostic from a car shop.

  • Initially, you should clearly make sure that the sound comes from the motor, and not from other parts. If a manual transmission is installed in the car, it is recommended to fully depress the clutch to disconnect the clutch from the engine. In this case, it will be possible to determine that the cause of the knock is located in the engine, and not in the transmission.
  • Then you need to listen carefully to the knock, determine its duration, cycle, and intensity. As noted earlier, even a certain level of tonality is characteristic of different faults.
  • A loud sound that is gaining momentum and coming from the upper region of the cylinder head -> a problem with valve clearances;
  • A sound similar to the impact of a small metal ball on the lid with a characteristic build-up -> a malfunction of the hydraulic compensator;
  • Rustling, whistling, and creaking sound -> a bad or failing timing chain or timing belt, as well as the alternator belt;
  • Detonation has a ringing, bright sound, usually the term ” knocking fingers”
  • It is also mandatory to check the condition of mounting the engine supports and, if possible, the entire chassis
  • To listen more carefully to the engine sounds, car owners often use a technical type phonendoscope device. Professional diagnostics involves the use of an engine tester like OBD 2.


Since diagnosing an engine knock is not a simple task, you should take your vehicle to a professional mechanic who is well-versed in this procedure and has the necessary equipment.

There are numerous causes for engine noise, including various forms of knocks. For the most part, these are signs of minor issues that the car may survive quietly for a long time. However, if a knock is heard, it may be an indication of more significant problems with the engine or its parts, and should not be ignored.

In order for the engine to work, numerous parts and components must work together and be subjected to high loads. The outgoing knock is a telltale sign of many different types of failures in internal combustion engines. Each knock has a unique tone, length, and strength.

It’s possible to detect the problem and fix it in a timely manner with meticulous diagnostics thanks to this.