Running a car on a frosty morning often turns into a stress test not only for the owner but also for the power unit itself. The driver freezes, waiting for the usual rhythmic hum, but instead hears a frightening metal clang or a deaf knock that thunder It can be short-lived, it can subside after a few seconds, or it can chase you until the coolant is fully warmed up.
Ignore such sound signals Engine Management System It is not worth it, as they are often harbingers of serious mechanical damage. Short knocking in the first 2-3 seconds after launch at low temperatures up to -15°C is considered a permissible physical phenomenon for some ICE designs. However, if the noise is intensifying or persists for a long time, it is urgent to look for the source of the problem.
In this article, we will discuss in detail why extraneous noises occur, how to distinguish harmless tapping from critical knocking and which nodes require the immediate attention of a mechanic. Understanding the nature of sound will help save significant money on overhaul.
Physics of the process: why the noise of the unheated engine
To understand why, we need to look at the changes that occur in the internal combustion engine during cold start-up. The metal parts that make up the unit have different coefficients of thermal expansion. As the temperature rises from the combustion of the fuel-air mixture, the gaps between the rubbing vapors change.
The main culprit is often motor oil. In the cold, the lubricating fluid thickens to become jelly-like, and loses its fluid properties. The pump cannot instantly deliver oil to the most distant lubrication points, such as a camshaft or hydrocompensators, creating an oil starvation effect in the first seconds of operation.
In addition, the thermal gaps between the piston and the cylinder, and between the rod and the crankshaft, are increased in the cold state. As the metal warms up, the gaps decrease to operating values, and the knocking can disappear. If the sound is not lost, then the wear of the parts has already gone beyond the permissible limits.
Lubrication system and hydrocompensators
The most common reason for the engine thunder It's a cold one, or it's a malfunction or a hydraulic compensator, and these devices automatically select the heat gap in the valve mechanism using the oil pressure, and if the oil is too thick or the feed channels are clogged, the compensators don't have time to fill.
The result is a characteristic metallic chop, which usually subsides as the oil is diluted, but if the system uses poor-quality lubrication or breaks the intervals of replacement, deposits form inside the compensators, which prevent them from working normally even hot.
It is important to check the oil levels and condition regularly, low lubrication causes the system to suffocate, which also causes noise, and in some cases, it helps to wash the engine with special compounds before changing the oil.
- 🛢️ Check the viscosity of the oil: for winter, brands with an index of 0W or 5W are suitable.
- 🔧 Evaluate the condition of the filter: a clogged filter restricts the flow of oil to the hydraulic compensators.
- ⚙️ Use a flushing liquid when switching to another brand of oil.
Never gas immediately after starting the engine in winter. Give the pump 10-15 seconds to pump the thick oil through the system before putting the load on.
Problems of the piston group: piston skirt and fingers
A more serious problem that causes the engine to rattle is the wear of the piston group. The knock of the piston against the cylinder wall is often called "slapping," which occurs when the gap between the piston skirt and the cylinder mirror becomes too large due to the output.
In the cold state, this gap is maximum, and the piston, when placed in dead spots, begins to beat against the walls. The sound is usually deaf, like hitting a tree or a stone. As the metal warms up, the gap expands, the gap decreases, and the noise can become quieter or disappear altogether.
The source of the sound can also be the piston finger, and if the sleeve in the top head of the rod or the finger itself is worn out, a ringing metal knock occurs, which often manifests itself not only at cold, but also at idle turns, and can be intensified by a sharp discharge of gas.
⚠️ Warning: If the engine is warmed up, the thud does not disappear, but only changes the tone, this is a sure sign of critical wear of cylinders or rod liners, and the operation of such a motor leads to jamming.
The chain of the GRM and tensioners: the source of the ringing clang
In engines where the transmission mechanism is driven by a circuit, the characteristic squeezing on the cold is a common occurrence. The problem is the hydraulic tensioner of the circuit, so while the engine is silenced, the oil can drain into the pallet, and when you start the chain is not stretched enough.
This causes the circuit to hit the sedatives and the shoes, and the sound is usually ringing, metallic, and localized to the front of the engine, and once the oil pump has created enough pressure, the tensioner will open and the clanking will stop.
However, if the tensioner is worn or coked, it may not hold the chain even on a heated motor. A stretched chain is a risk of jumping teeth, which in modern interval motors leads to the meeting of valves with pistons and expensive repair of the block head.
How to check the tension of the chain indiscriminately?
Ask the assistant to cut off the air supply at the inlet for a short time (carefully!), creating a vacuum. If at this point the chain clang disappears, then the tensioner is working, but the chain is stretched or the shoes are worn out.
Diesel knock and features of TNVD
Diesel car owners are familiar with the characteristic roar that is often confused with a malfunction. In fact, the hard ignition of fuel in a diesel always comes with a louder sound of operation than that of gasoline counterparts. However, excessive knocking can indicate problems.
Often the cause is fuel equipment, and if the injectors pour fuel or have the wrong spray torch, the combustion happens too abruptly, causing a knock, and the source of the noise can also be a THVD drive mechanism or a high pressure pump.
Cold diesel has a high viscosity, which makes it difficult to pump and spray. Using summer diesel in winter is guaranteed to cause the engine to rattle and start poorly until the fuel in the tank is mixed with warm or replaced.
| Type of sound | Probable cause | Danger. | Action |
|---|---|---|---|
| The belling tinkle | Hydrocompensators | Medium | Oil change, filter check |
| Deaf knock | Reciprocating wear | High. | Diagnosis of compression, repair |
| Metal clang | The GRMA chain | Critical | Replacement of chain and tensioner |
| Rhythmic tapping | Craft liners | Critical | Urgent stop, overhaul. |
Diagnosis: How to determine the source of noise
To determine the exact reason why thunder If you put a tool on different parts of the cylinder block, you can localize the sound source, and if you put a hose in the home, you can use one ear to it and the other end to drive the engine.
Be sure to check the attachments. Sometimes the generator, pump or belt rollers make sounds very similar to the sound of the internals of the engine. Remove the belt of the drive units and start the engine briefly. If the sound is gone, the problem is not the engine.
Also worth paying attention to the pillows (pillows) of the engine. If they are destroyed, the motor can touch the body or elements of the hood space, transmitting vibration and knock. Visual inspection of the pillows for cracks and tears is mandatory.
☑️ Primary diagnosis of knocking
Remediation methods and preventive measures
If the diagnostics show that the engine is thundering due to wear and tear of the internal components, mechanical intervention is necessary. Replacing pistons, rings, liners or a GRM chain requires opening the engine. Attempts to use “knock additives” are temporary and often only mask the problem.
In the case of hydraulic compensators, sometimes it helps to decoct or use a more liquid oil, but if the mechanism is already worn out physically, only replacement will help. For chain motors, timely replacement of the circuit and sedatives is the key to a long life of the motor.
The main preventive measure is quality and timely maintenance, the use of original filters and oils that meet the manufacturer's tolerances. Vehicle ManufacturerIt minimizes wear and tear during cold starts. Don't skimp on lubricants, engine repairs are much more expensive.
⚠️ Attention: The use of washing oils "five-minute" on older engines with high mileage can lead to the separation of large fractions of the soda and blockage of oil channels, which will cause oil starvation and wedge.
Timely oil change and the use of quality filters prevents 80% of the problems with the engine knocking on the cold, associated with the lubrication system.
Frequently Asked Questions (FAQ)
Can I drive if the engine only knocks on the cold?
If the knocking takes place 2-5 seconds after starting and the engine is running smoothly, short-term operation is possible, but requires observation, but if the sound persists longer or manifests itself on hot - you can not drive, this will lead to the destruction of the engine.
Will switching to a thicker oil help?
Switching to a thicker oil (e.g., from 5W-30 to 5W-40) can temporarily reduce the noise of hydraulic compensators and piston, as the thicker film better fills the gaps. However, this is not repair, but only a measure to reduce acoustic discomfort.
Why does diesel knock harder than gasoline?
The diesel engine works by self-ignition of the fuel at high pressure, which creates a sharper jump in pressure in the cylinder. This is a design feature that causes a characteristic "diesel roar" that is not a malfunction.
Is the thud of hydrocompensators dangerous?
By itself, the hydraulic compressors will not cause instantaneous engine destruction, but it signals disruption of gas distribution or lubrication phases. Prolonged driving with faulty compensators can lead to valve burnout.