Engine Flushing: What Is It and Why Do You Need It

Published on 8 Feb, 2022, 4:50 AM IST

Updated on 28 May, 2025, 6:30 AM IST

Team Ackodrive

10 min read

Interesting Articles

The engine is the heart of your car, keeping it running smoothly and in motion. While regular oil changes and routine maintenance are crucial, proper engine care involves more than just replacing the oil. One critical yet often overlooked process is an engine flush for the car. This procedure becomes particularly important in cases of inconsistent oil changes, prolonged periods of vehicle inactivity, or when facing engine-related issues. This article explains the engine flushing process in detail, highlighting its benefits and the situations in which it should be considered.

Contents

What is Engine Flushing?

Engine flushing is the process of cleaning out sludge, carbon deposits, and other contaminants that accumulate on the internal components of an engine over time. It involves the use of engine flush oil or specialised additives designed to dissolve and remove these impurities. By clearing out built-up residue, engine flushing helps restore engine efficiency and prolong its lifespan.

Carbon deposits or sludge formation inside the engine can result from various factors, including engine ageing, use of low-quality fuel or engine oil, improper fuel composition, and irregular oil changes. This build-up can significantly reduce power output and lead to other performance issues. In such cases, an engine oil flush can help clean the internal components and restore optimal engine function.

Engine Flushing: Why Do You Need It?

The answer to this question depends on various factors such as the vehicle’s age, maintenance history and engine performance. The following points explain the different scenarios where your car may need engine flushing.

If the vehicle is old or has covered more than 40,000 km, then your car needs an engine flushing. With more and more kilometres, the engine's internals are prone to carbon deposits and sludge formation. Hence, the flushing process keeps the engine healthy, and you will not experience any performance drop.
If the car is not maintained correctly or the engine oil is not changed as per the manufacturer's recommendation, the chances of sludge build-up are high. Flushing the engine can clean the internals of the engine.
If you continuously drive your car in stop-and-go traffic or drive only a few kilometres per month, then you should consider engine flushing every 30,000 to 35,000 km. That's because driving under such conditions causes the engine oil to leave deposits, and flushing the engine cleans the sludge buildup.
Your car requires engine flushing if it's parked for a very long time. The engine oil can build up sludge, and it can damage the engine's internals. Hence, it's advisable to clean the internals before driving the car.

How is Engine Flushing Done?

Engine flushing is a simple process which requires a high-grade engine flush additive to remove the sludge and carbon deposits inside the engine.

There are three methods of engine flushing. Your mechanic will determine the best method depending on your car's engine condition.

Method 1: Take Your Car Out For a Short Drive

Here’s how the engine oil flush process is typically carried out:

Drain out a small amount of oil from the engine.
Add the engine flush additive through the oil filler port.
Next, you take the car for a short spin so that the chemical can reach the nooks and crannies of the engine.
The chemical composition removes the sludge and carbon deposits. The impurities get settled in the oil and the oil filter.
Finally, the mechanic changes the oil filter and engine oil.

Method 2: Engine Idling

Engine idling is a key part of this engine oil flush method, and the process typically involves the following steps:

Drain out a small quantity of engine oil and pour the additive via the engine oil filler port.
Start the engine and let it idle for around 5 to 10 minutes. Note that this method does not require you to take the car for a short drive.
The engine flush additive circulates throughout the engine and loosens up the sludge.
The impurities get deposited in the oil filter or settle on the oil sump.
Lastly, the mechanic changes the engine oil and replaces the oil filter.

Method 3: Drain Out the Oil and Flush

This step includes draining the old engine oil and applying engine flush oil to eliminate built-up contaminants. The process involves the following steps:

Drain the engine oil as you would during an oil change.
Pour clean engine oil and the flush additive into the oil filler port.
Start the engine and let it idle for a few minutes. The chemical mixed with the oil circulates to every corner of the engine.
The additive clears the sludge/carbon deposits, and it gets settled in the oil filter or oil sump.
Finally, the mechanic can change the oil and the fuel filter.

Benefits of Engine Flushing

Here are the advantages of engine flushing:

Engine flushing prevents and removes sludge formation. It saves you from hefty repair bills by avoiding the harmful effects of sludge on the internal engine components.
Flushing also removes carbon deposits that form over time.
If the vehicle is parked for an extended period or you don't drive the car as much, the engine is unused. It's a perfect condition for sludge formation. Performing an engine flush in such a scenario can improve the engine's longevity.
If you are purchasing a used car and do not have any documents related to engine maintenance, an engine flush can save you from costly repairs.
An engine flush cleans the internal parts of the engine, and in turn, it results in the efficient functioning of the engine. An efficient engine returns good fuel economy.

How Does Engine Sludge and Deposit Form?

The following points explain how sludge and deposits form inside an engine:

Engine oil circulates throughout the engine and lubricates all the moving components. In other words, engine oil should be in motion inside the engine.
When you don’t drive the car for a very long time, drive in stop-and-go traffic or drive very short distances for a very long time, the engine oil starts leaving deposits on the internal components.
Apart from sludge, carbon deposits also build up over time. They are nothing but the by-product of improper fuel combustion. Similar to sludge, it gets collected on the internals of the engine. It can lead to a performance drop.
The deposits keep building up and forming sludge. The sludge can hamper the oil flow inside the engine.
If ignored, it can lead to severe problems like malfunctioning spark plugs, valves and essential sensors. You may also find soot coming out of the exhaust if there is too much sludge formation inside the engine.
In the worst-case scenario, you may need to replace the engine if it gets seized due to the lack of lubrication.

Engine Oil Sludge Formation: How to Determine

So, how do you determine the formation of sludge inside your car’s engine? It does not require extensive knowledge about the functioning of an engine. All you have to do is keep an eye on some of the symptoms that point towards engine sludge. Below are the symptoms of an engine with excessive sludge formation.

Check engine light: Your car’s check engine light may light up if there’s an issue with the engine components. The sludge/improper oil flow can damage the components and sensors. Hence, the engine check light will warn you about the malfunction. It would be best to immediately visit the service centre when this light comes on.
Check oil light: A check oil light turns on when there’s insufficient oil or low oil pressure. The latter is caused due to sludge inside the engine. The thickened engine oil can also trigger the check engine light. Whatever the reason might be, you should immediately get the engine checked when you see this light on your car’s dashboard.
Low fuel efficiency: The engine is stressed and has to work harder due to the thick and sticky sludge deposited on the engine components. It results in increased fuel consumption. In turn, it will reduce the fuel economy. If the mileage drops without you changing your driving style, it indicates sludge formation.
Engine overheating: As mentioned earlier, the role of engine oil is to lubricate the moving internal components and reduce friction. The sludge does the exact opposite. It increases friction between the moving engine components. The friction causes heat, leading to an engine overheating problem. If your car overheats, it may be due to sludge formation.

Takeaway: Is Engine Flushing Worth It?

Engine flushing is not required for every car, but it can be highly beneficial in certain situations. If your vehicle has been poorly maintained, left unused for long periods, or driven in heavy traffic conditions, engine sludge and carbon deposits may build up. An engine flush helps clean these contaminants, improving performance and fuel efficiency. It's particularly useful for older cars, vehicles over 40,000 km, or when buying a used car with an unclear service history. While not a substitute for regular oil changes, engine flushing can extend engine life when used appropriately and performed by a professional or using the right products.

Frequently Asked Questions

Here are some of the most commonly asked questions about car engine flushing.

What is the purpose of the engine flush?

The primary purpose of an engine flush is to clean out sludge, carbon deposits, and other contaminants that build up inside the engine over time. This helps improve engine efficiency, restore performance, and prolong the engine’s lifespan by removing impurities that regular oil changes may not fully eliminate.

How do I know if my car needs an engine flush?

Signs that your car may need an engine flush include reduced engine performance, rough idling, unusual noises, excessive exhaust smoke, or if the oil appears thick and dirty even after a recent change. If the vehicle has experienced irregular oil changes or has been unused for extended periods, an engine flush could be beneficial.

What happens after an engine flush?

After an engine flush, the loosened sludge and deposits are drained out along with the old engine oil. A new oil filter is usually installed, and fresh engine oil is added. This results in a cleaner engine, smoother operation, and often better fuel efficiency and power delivery.

How to flush engine coolant?

Flushing engine coolant involves draining the old coolant from the radiator and engine block, flushing the system with a cleaning solution or water to remove rust and deposits, and then refilling with fresh coolant. This process helps prevent overheating and corrosion inside the cooling system.

How to remove engine sludge?

Engine sludge can be removed by performing an engine flush using specially formulated additives, engine flush oil, or engine cleaning liquid. These chemicals break down sludge and carbon deposits, allowing them to be drained out with the old oil. In severe cases, manual cleaning or professional service may be required.

What can I use as an engine flush?

Engine flush products typically come in the form of specialised additives or engine flush oil designed to dissolve sludge and contaminants. It’s important to use a product specifically made for engine flushing to ensure effectiveness and avoid damage.

How much does an engine flush cost?

The cost of an engine flush in India typically ranges between ₹4,000 and ₹12,000, depending on the vehicle type and service provider. DIY engine flush products are also available at a lower cost but require careful usage to avoid any engine damage.

What is engine flush cleaner?

An engine flush cleaner is a chemical additive used to break down and remove sludge, carbon deposits, and other contaminants inside the engine. It’s added to the engine oil before draining to clean internal components and improve engine health.

Explore More: