Engine knocking on cold start. Knocking diagnostics.

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Why does knocking occur in engine? What is the reason?

Knocks in the engine appear on cold and hot. Engine knocking on cold occurs both in winter and summer. Today we will consider the reasons of knocking when power unit is running on cold. Let’s find out how to independently diagnose the engine.

Anything can knock in the power unit. There may be noises in the attachments. For example, the bearings of a generator or water pump make noise. Also it could be the noise of connecting rod bearings or pistons.

Engine knocking

The main reasons for engine knocking are as follows:

  1. Oil sump problems: not enough oil.
  2. The power unit is operated with poor quality oil filled. Lubricant replacement times are ignored or missed.
  3. ICE (internal combustion engine) operation with increased constant loads. It can be an aggressive manner of driving a vehicle or violation of speed limits.
  4. The engine often overheats.
  5. Parts of the crank mechanism and/or cylinder-piston group were worn out.
  6. Knocking engine valves if incorrectly adjusted.
  7. It may be caused by problems with attachments: the timing belt, pump, hydraulic power steering, other pulleys, and so on.

As for diesel power units. Usually, this is the problem of knocking plunger pair of injection pump.

Keep in mind!

You can extend the operating period of the internal combustion engine. It must be regularly serviced for this. For example, oil and filter elements should be changed after 10-15 thousand km of car mileage.

If the vehicle is operated in difficult weather and road conditions, the lubricant should be changed more often.

The point is that due to the increased friction of parts, the engine oil darkens faster. In addition, it loses its lubricating properties.

Photo: see what an untimely change of the lubricant can lead to. Anything will knock in such engine!

If there is a knock in the engine, it is necessary to stop operating the vehicle and send it to service center for diagnostics and maintenance.

Experts will determine where the knock comes from when starting the engine, using modern scanning tools such as device and motor tester. But, you can find out the reasons for engine knocking independently.

Engine knocking

Knocking diagnostics by yourself

You can find out where the knock in ICE comes from.

It is important to make sure that the sound is coming from the engine.

Pay attention!

If the engine aggregates with a manual transmission, it is necessary to disconnect the power unit by pressing the clutch.

Turn on the engine:

  1. Listen to where the metallic sound is coming from.
  2. Try to understand the cyclical nature of the sound and its intensity.

By tonality you can determine which malfunction it belongs to:

  1. Gaining sonorous blow from the top of the cylinder head may indicate problems with valve clearances.
  2. A blow sound resembling a falling ball indicates a malfunction of the hydraulic compressor.
  3. A creaking or rustling sound indicates a malfunction of the timing belt or chain.
  4. A whistling sound may indicate the unstable operation of the generator belt.
  5. Finger tapping sound indicates the knock.
  6. The emerging sound can come from engine support and even the chassis of car. Checking the attachment will help to make sure.

Technical phonendoscope can be used to identify the problem.

What is the risk of knock?

Knock can affect piston operation and lead to mechanical damage to the cylinder walls. This, in turn, accelerates the wear of the power unit parts. To minimize the risks, special knock sensors should be installed on cars.

They must track vibrations in the engine cylinders. Finding inconsistency the signal goes to the electronic control unit. The car’s brain adjust the fuel mixture and ignition. But this cannot fully counteract the appearance of extraneous noise. If there is a knock, then the engine can start knocking:

  1. Immediately after starting at idle speed.
  2. When the gas pedal is pressed hard.
  3. Under a load during car operation.
  4. When an inappropriate transmission is selected etc.

ICE knock can occur on cold if low-quality fuel is used or a low-octane product is poured into the tank instead of the recommended high-octane fuel.

Another reason for knock is the increased compression ratio. This is due to:

  1. Installation of a thin cylinder head gasket.
  2. Incorrect repairs.
  3. Unauthorized interference in the power unit in order to raise its power to a higher level, which differs from the factory settings.

What cars have the loudest engines?

The noisiest engines are installed in Volkswagen Polo, which production is taking place in Kaluga (Russia). It’s about cars with engine volume of 1.6 liters in three versions.


The engine problem is the sound of pistons, which occurs on cold. This is due to the design features of cylinder-piston group. It is almost impossible to cope with the problem and it makes no sense. The fact is that the noise disappears after warming up the internal combustion engine.

Another problem is knocking due to unstable operation of hydraulic tappets. This problem is not common and it can be hardly classified as main malfunction.

“Loud” Renault can be distinguished among diesel engines. We are talking about DCI diesel engine with a volume of 1.5/1, 9.2/2 liters. These are French cars, produced in 2001-2009. The noise comes from the crank mechanism. It is important not to overheat these diesel engines and change the lubricant timely.

The weakest link in the diesel lineup is 1.5 liter engine. Owners often complain that the connecting rod bearings turn around after 130-150 thousand kilometers mileage.

A few words about the service

If there is a knock in the engine, most of us go to the service center and hope for qualified help. Unfair experts sometimes insist on overhaul after engine checking. Although sometimes it is enough to change the oil and the unpleasant sounds will disappear.

Or take another example: appearing of extraneous sounds when car acceleration. But, surprisingly, the problem may be the timing chain. We don’t even mean it because of its long useful life. But during intensive using of car the chain tends to stretch and begins to rattle in contact with the block body. And we think these are internal combustion engine problems. Having discovered the reason, car service experts may not say about it and will recommend the engine overhaul. Nevertheless, it will be enough just to tighten the timing chain and say goodbye to the problem for the coming years.

Therefore, it is important to distinguish sounds independently and be able to carry out a set of diagnostic measures. Then you will not be confused at the car-service station with their false proposition to do difficult maintenance.

In conclusion

We have considered the reasons for the engine knocking on cold. We found out how to identify possible problems independently. The power unit is one of the main elements of vehicle. Due attention should be paid to it. Engine care, timely oil change and gentle use will prolong its smooth operation.

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