Why Does My Car Engine Knock On Startup Then Goes Away?

Are you curious about why your car has an engine knock when you start it, which then disappears? This could be attributed to several factors, and it often occurs in vehicles that have been driven more than 200,000 miles. Some cars may show this issue earlier on, but in most situations, it’s not a deadly problem.

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Engine knock on startup can result from minor issues like stocky filters, carbon buildup, or piston slap. Significant causes of engine knock on startup may include worn-out vehicle components as well as worn-out engine parts. 

This article will take you through the entire issue, how to diagnose the problem and what you can do to fix the issue. Moreover, you will learn the cost of making the repairs and what to keep in mind throughout the entire process. 

What should you do if your engine knocks on startup then goes away?

Firstly,

If your engine knocks on startup then go away, you will need to warm up the engine for a few minutes. This is a great idea, especially when you hear the noise only once in a while rather than regularly.

Heating up the engine has a few benefits, such as warming up the engine components like the crank, which contracts on cooling, especially in older vehicles. Warming up the engine ensures that the components and oil get sufficient heat to reach normal working conditions. The engine will be less likely to develop the engine knock if the issue is caused by component wear or oil issues. 

The next thing you should do is take the vehicle to your local mechanic shop for a checkup. Some issues may be easy to diagnose by yourself, but a trained professional may identify other underlying problems. The related problems may include things like engine overheating and engine oil leakages. 

A mechanic will be able to diagnose and identify the issue in a matter of minutes or a few hours. Once the issues have been identified and fixed, you can do a few maintenance procedures to prevent other problems from arising. 

Next steps

Ensure you keep using high-quality engine oils in your vehicle. The recommended engine oil for your car of good quality will help prevent engine wear and tear. Besides, proper lubrication will ensure that the engine components are damaged due to the rapid expansion during startup. 

The vehicle’s manual will show the needed viscosity grade of the best engine oil for your car. You can also choose to include engine oil additives in the mix to prevent a lot of heat generation and also help improve the lifespan of engine components.

The oil additives perform other special functions like cleaning engine debris, increasing fuel economy, and preventing engine knock on startup. 

Engine tuning is another great way to improve engine efficiency, reliability, and performance. Engine tunes like adjustments of the spark plug timing will ensure the ignition is done precisely to improve performance and fuel economy. Regular filter changes help reduce sludge and debris buildup.

Another great practice to help prevent engine knock on startup is to ensure you always respond to the check engine light. Early detection of vehicle problems will save you a lot of money and prevent major plus recurrent issues.

The common causes and how to fix these problems

Piston slap

Piston slap is an issue that is common in vehicles with more than 180,000 miles on them. It is when the cylinder wall and the piston are not tightly fitted together as you would expect in newly bought vehicles. The components wear off with age which increases the tolerances between them. This leads to developing a rocky piston that moves side to side instead of just up and down.

The issue may not be due to wear and tear in some rare cases but rather a design flaw. In that case, the pistons and cylinders need to be properly checked and redesigned to fit suitably. Piston slap forms due to friction resulting in physical wear for most situations. Physical wear can be because of age or poor lubrication of these engine components.

Here are the steps to follow to identify and solve this issue:

1. Start by opening up the engine bay to access the pistons. You will need special tools like wrenches and screwdrivers. Arm yourself with a mechanic’s toolbox.
2. Proceed to disassemble the engine to access the pistons and cylinders.
3. Visually inspect the piston and cylinder walls for any side-to-side motion or a slight angle inclination of the piston. The tolerance should be tight and the up and down movement smooth.
4. Take note of any wear and tear of the pistons and the cylinders.
5. If the design is flawed, proceed to replace worn-out components or perform a piston-cylinder rebuild. Remember that engine rebuilds are expensive and need to be done by experts.
6. Reassemble the engine and take note of whether the issue has been resolved.

Sticky engine lifter

Engine/valve lifters are located between the vehicle’s cylinder valves and camshaft. These lifters are other frequent causes of engine knock on startup. The noise caused by sticky engine lifters is usually a loud ticking sound distinct from other engine knocks. 

The most significant cause of sticky valve lifters is insufficient lubrication from the engine oil. Therefore, you can quickly solve the sticky engine lifter problem by regularly changing the car’s engine oil. You can also add in some engine oil additives for further protection and perform engine maintenances regularly. 

Vehicles with hundreds of miles are more likely to develop this issue due to more gaps that the engine oil cannot accommodate. This will lead to less lubrication and the development of mechanical noise. 

Here are the steps to follow to identify and solve this issue:

1. Open the engine bay to inspect the engine lifters visually. 
2. Remember the time it takes for the engine knock on startup to go away, as it will help you determine the cause of the sticky engine lifters. Proceed to take note of the wear and tear of this component since more prolonged noises may mean the part needs to be changed. 
3. Take a look at the associated components such as the springs, valve lifters, and pushrods. Poor attachment and tolerances between these connected parts may also cause the sticky valve lifters. Proceed to connect them correctly to fix the issue. 
4. If all the above are in suitable conditions, you will conclude that the engine oil is the issue. Go ahead and use the proper engine oil with the right viscosity and properties as stated in your vehicle’s manual. 

Worn engine parts

The worn engine parts can cause engine knock/or be mistaken for engine knock during startup, including water pumps, alternators, and steering pumps. The good thing about noise from worn engine parts is that it is normal, and your vehicle will function appropriately till the particular part fails. The check engine light will let you know where the issue lies. 

The noise from worn engine parts is usually harmonic and rhythmical but will disappear after the startup. This is because the engine oil will properly circulate through the parts after the engine has been warmed up for a while and the startup is done. The parts such as bearings will expand due to the heat, and the operations will become smoother regardless of wear and tear. 

Here are the steps to follow to identify and solve this issue:

1. Take a look at the check engine light to help pinpoint the component that may be causing the issue. 
2. Proceed to open up the engine and visually inspect the various parts like the valves, springs, alternators, and exhaust manifold. 
3. Take a look at the lubrication level of the parts since engine oil may be leaking, causing more wear and tear. 
4. Proceed to replace the worn-out components and provide enough lubrication for the engine parts. 

Bearing worn-out

Bearings help shafts and other rotating components to move smoothly. These rotating engine components are critical to how smoothly the engine runs. Once they become worn out, the engine will make noises, including the engine knock on startup. Moreover, worn-out bearings can lead to piston slap which will cause the problem.

The most affected bearing is the crankshaft’s main bearing, which causes the crank not to connect with other components correctly. The problem goes away once the crankshaft is heated enough to expand slightly. However, the issue reoccurs once the temperatures are low and the crank contracts. 

Here are the steps to follow to identify and solve this issue:

1. Open up the engine and take a look at the crankshaft and the center main bearing. 
2. Visually inspect any wear and tear on the components and the tolerances of the connected components. 
3. You can look at any metal shavings on the components and how lubricated the parts are. Pay attention to the oil condition as this is a contributing factor to the deterioration of the bearing. 

Oil drain-back

Oil-drain back is when the engine oil is not well sealed in the engine block and drains from the block through the check valve. A faulty check valve won’t be able to seal the engine block properly, which will allow for oil leaks through the oil filter where the valve is housed.

The consequence is that the oil pump pushes the oil through sensitive components that are not meant to be accessible. The noise will persist for a few seconds when you start up the engine. But it will cease once the oil is fully pumped through and can lubricate the parts. Even though the oil will protect the parts while the engine is running, the issue will still reoccur when you start up the vehicle.

Here are the steps to follow to identify and solve this issue:

1. Start by visually inspecting the oil filter once you have opened up the engine.
2. Proceed to check the check valve to see how well it is fitted.
3. Oil marks on sensitive components that shouldn’t be accessible by the oil will be a clear indicator of oil drain back.
4. Go ahead and replace the oil filter with a high-quality one to keep the oil in the engine block. Avoid cheap oil filters since they come with less efficient check valves or no check valves whatsoever.

Build-up carbon on engine

Older vehicles are more likely to develop carbon buildup than newer vehicles. Carbon buildup in the engine is generally caused by the incomplete combustion of fuel, leading to the creation of black soot. 

The buildup is terrible for your engine since it will cause the components to harden on. Affected parts may include the cylinder walls and intake valves. This will cause motion difficulties and also create noises when the engine starts. The knock will go away once the engine oil circulates appropriately through the engine and lubricates the affected parts. 

Here are the steps to follow to identify and solve this issue:

1. Take note of the quality of your engine oil. Dirty engine oil will indicate there is a lot of dirt and carbon buildup in the engine, causing performance issues. 
2. Proceed to do an oil change and an oil filter change if the oil is dirty. 
3. You can then go ahead to disassemble the engine and physically clean away any carbon on the engine parts with solvent. Steel wool can also help with soaking the disassembled engine parts for about 15 minutes. 
4. Reassemble the engine.

Read more: What Happens If You Don’t Change Your Oil?

How much does it cost to fix the problem?

Several factors affect the cost of fixing an engine knock on startup. Some factors include the need for an oil change if design flaws exist in the engine, the condition of engine components, the price of replacement parts, and labor costs for various fixes.  

On an average basis, you can expect to spend $2,000 – $5,000 for a rebuild or as low as $250 -$500 for carbon buildup cleaning and engine oil/oil filter changes. 

Conclusion

Engine knock on startup is a common issue that is rarely a significant issue that should cause an alarm. The most common causes include piston slap, component wear and tear, sticky lifters, and worn bearings. Most of these causes can be dealt with by regular oil changes and keeping the engine components well lubricated. 

Read more: Car Shakes When AC Is On: Why and How to Fix It