- What Causes The Knocking Sound?
- Exhaust System Contracting
- Cold Weather
- Loose Engine Mount Or Driveshaft
- Cooling Fan Off Balance
- Reduced Oil Pressure
- Using The Wrong Spark Plugs
- Pulleys And Belt Tensioners
- Damaged Head Gasket
- Coolant Tanks
- Solutions To the Car Knocking Sounds
- Always Check The Sensors
- Replacing Your Rod Bearings
- Regular Servicing Of Your Vehicle
- Replace The Spark Plugs
- Fuel Detergent
- Changing The Oil And Filter
- Final Verdict
Is everything okay? I know that is the first question you will have once you hear a knocking after turning the engine off.
Having your car checked anytime, you have doubts or there are weird noises will save you money and disappointments in the future.
Although the car knocking sound after turning off the engine is not always an indication of a problem, being sure doesn’t hurt.
Every car owner understands how delicate and expensive a car’s engine is. I’m sure you do not want to be in a position where you must change your engine.
Tackling the engine problems head-on will help avoid any future losses or problems.
Below are some causes and solutions to a car knocking sound after turning off the engine.
What Causes The Knocking Sound?
Let’s dive in and look at all the possible causes of the knocking sound.
Exhaust System Contracting
After a long drive, while using a turbo-powered car, you might hear a knocking sound after turning off the engine.
It is a result of the contraction of the exhaust system. The sound is typical, and you don’t have to worry about it.
You can always avoid it by letting the car run for a minute after a long drive off. You can also consider using a high fuel octane rating.
It is highly likely to experience a car knocking sound after turning off the engine on freezing days or in the winter.
After the car is turned on, heat is generated, and once it’s shut off, the metal parts contract due to the cold; hence, the knocking sounds after turning off the engine.
Loose Engine Mount Or Driveshaft
Loose engine mounts could also result in a knocking sound after turning off the engine.
When the driveshafts or engine mounts get loose, the engine also becomes loose and starts moving around, hence the knocking sounds.
The only solution to this problem is having these mounts checked and fixed before more trouble escalates.
Cooling Fan Off Balance
You might also experience car knocking sounds after turning off the engine if the cooling fan is not in the correct position.
The fan could be hitting something and hence the knocking sound. Let someone else turn the car off after the fan has been running and check how it’s positioned.
Reduced Oil Pressure
During shut-off, oil pressure reduces due to the sudden stop. In most cases, the knocking sounds occur in the last spins before the car shuts down completely.
It takes less than a second.
Most vehicles are now computer-controlled and have sensors that can detect every problem in the car. The sensors will alert you every time there is a problem.
A signal is first sent to the engine control unit to fix the problem.
Sometimes even after the problem is corrected, the sensors will still alert you; if you are shutting off your car, you will probably hear the knocking sound after the engine is turned off.
Using The Wrong Spark Plugs
The wrong spark plugs may fail to ignite all the fuel causing a knocking sound after turning off the engine. You can quickly identify bad spark plugs.
Sometimes the spark plugs may be worn out and require a switch, or you are simply using the wrong type of spark plugs in your vehicle.
Pulleys And Belt Tensioners
The knocking sounds after turning off the engine might seem like they are coming from the engine, while it’s not the case.
There is a variety of moving equipment down there, and as the car moves, they might collide, causing a knocking sound.
After the engine is turned off, the engine accessories and all other equipment do not halt abruptly.
On the contrary, they turn a few more times, causing the knocking sound. Another major cause of the knocking sound after turning off the engine is a faulty lifter.
The sounds could be alarming or not, depending on the magnitude of the destruction.
If the knocking sound is too much or proceeds for a long time, it could indicate too much destruction.
However, if the knocking sound is brief, it may result from accumulated dirt and dust.
Damaged Head Gasket
A damaged oil gasket will cause knocking sounds when driving and after turning the engine off.
The reason is that it exposes the coolant system to external materials like dust particles.
Another cause of the knocking sounds after turning off the engine is the coolant tanks.
Some vehicles come with coolant tanks that create some noises after the engine is turned off. In most instances, the noise is no problem at all.
Solutions To the Car Knocking Sounds
Having learned the different causes of the engine knocking sounds, you must identify ways to solve the problems.
Most of the time, the sounds are not alarming, and you only need a check-up to get everything cleared out.
Always Check The Sensors
A bad knock sensor will misinform you. Therefore, ensuring your sensors are okay and working will help avoid any problems in your car or misguided information.
Replacing Your Rod Bearings
Whether you use your car regularly or once in a while, you need to get the bearings checked.
Some people can tell when the bearings require changing, and some will get an idea after an engine knock.
Having the engine and all accessories changed after continued use can solve the problem of a knocking engine.
Regular Servicing Of Your Vehicle
As we have seen earlier, the knocking sound is probably not coming from the engine.
If your vehicle is serviced regularly, your mechanics can realize what needs to be changed or what could bring about any weird sounds or other problems.
Replace The Spark Plugs
Different spark plugs are made for different temperatures. The wrong spark plug will experience heat intolerance hence a spark knock.
Carbon build-up usually coats the electrodes and narrows the gap resulting in the knock.
It would help if you used the correct spark plugs for your vehicle and maintained the proper gap.
Fuel detergents help a great deal in preventing engine knocks.
The detergent fuels help reduce carbon accumulation in the cylinder walls and on the spark plug electrodes.
The accumulated carbon causes premature fuel-air detonation and, after that, a knocking sound.
Therefore, getting file detergent and more suitable fuel detergent will prevent engine knocks after the engine is off.
Changing The Oil And Filter
Oil is an essential aspect of every engine. Some engine problems emanate from substandard oil or failure to oil the different parts.
Engine knocks can occur when different parts collide, especially if not oiled.
Lubricating the different engine parts helps distribute oil and remove metal filings and other dirt particles.
Also, using good-quality lubricating oil will help a great deal in avoiding engine knocks.
You never know what to feel about an engine knock. Sometimes, it may be a warning of a roaming problem, while in some instances, it is a non-issue.
In most cases, only mechanics and trained personnel can identify whether a particular engine knock indicated a red flag or not.
While it’s not always a cause for alarm, you should always have it checked after experiencing knocking sounds after turning off the engine.
James has been a car enthusiast since his childhood when he learned the differences between a ford and a chevy from his father. He loves to drive and restore old cars with a special drive for Italian marvels. Currently, he has a 1968 Alfa Romeo. He has studied aeronautics and civil aviation in his college and still gets smitten by Galant SS and Lancer GSR.
He is a New York-based product training director working with a giant automotive retailer. He loves to review and uncover the vehicles and their fascinating stories. He believes in keeping it legitimate with a keen passion for research on the latest technological upgrades in cars. While reading his articles or blogs, you can sense the extensive research and dedication backing the piece of text. He loves fried chicken, music, and spending quality time with his pet dog.
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