What is an engine flush, and do you need one?

Ask the Mechanic

As your vehicle accumulates kilometers, your mechanic may recommend an engine flush depending on how you’ve maintained your car, more kilometers may also mean the accumulation of contaminants. While scam products that solve non-existent problems are out there, engine flushes were designed with the more legitimate contaminants in mind.


What is an engine flush?

 An engine oil flush cleans the engine’s internal parts of excess oil, dirt and sludge built up over time. A small amount of oil is removed from the engine. Next, a nonsolvent flush additive chemical, designed to break up carbon deposits in the engine, is added to the system. Then, the car is taken for a test drive to work the chemical through the engine. An engine flush also helps remove corrosion inhibitors to help extend the life of motor oils. This can result in reduced oil changes throughout the vehicle’s lifetime.


How does sludge form in an engine?

Oil sludge is a gel or solid in your engine oil caused by wear and contaminants. How does sludge form? The longer oil stays in your engine, the more it oxidizes and picks up contamination as it cleans and lubricates the engine. Common causes of contamination and oxidation are:

Oil breakdown

Engine oil is subjected to a variety of harsh conditions throughout the life of an engine, resulting in degradation over time.

Thermal degradation

Thermal degradation results from excessive heat caused by friction between metal parts inside an engine.


Oxidation occurs when oxygen chemically reacts with the engine oil the primary purpose for using antioxidants.


Corrosion happens when additives designed to minimize wear within the engine meet water vapor or humid air drawn into the crankcase because of its low boiling point.

Any of these may result in fuel contamination, meaning the oil breaks down into corrosive acidic compounds once inside the combustion chamber. As it further degrades, oil loses viscosity and forms sludge.

Fortunately, you can protect your car from the accumulation of engine sludge by keeping up with factory-recommended maintenance. Ignoring check-ups and oil changes puts your vehicle at risk of developing costly problems such as engine sludge


Engine flush pros


Decreased engine wear

Using an engine flush on a high-mileage engine will clean the engine of accumulated sludge, carbon deposits and contaminates that increase engine wear. A flush can also increase performance and fuel economy.

Cleans internal parts

An engine flush will clean the engine components you can’t see that would otherwise require a complete engine teardown.

Improved fuel economy

When sludge and contaminants increase, so does the engine oil viscosity. This thicker oil can increase wear and resistance, requiring the engine to work harder. Eventually, your fuel economy will be affected, and your engine will feel sluggish.

Better emissions control

Carbon deposits and contaminants can cause piston rings to stick. Deposits can eventually cause damage to the piston rings and combustion chamber walls. As a result, the oil will make its way past these areas and enter the combustion chamber, causing high oil consumption and burned oil in your exhaust emissions.


Engine flush cons


Other motor issues may appear

On the flipside, removing sludge and unwanted deposits may also be the reason not to get an engine flush. For example, older high-mileage engines with built-up sludge may rely on the sludge to cover cracks and openings in worn-out seals. Once the sludge is gone, fresh oil will flow through those cracks and allow oil leaks in or out of the engine.


How often should you do an engine flush?

Suppose you purchase or own a vehicle with a sketchy or unknown oil change regimen. In that case, an engine flush can help remove sludge and contaminants from years of neglect and prepare the engine for new oil and a new filter.

If you don’t fall into that category and have followed recommended oil changes, you probably won’t need an engine flush as part of your vehicle’s regular maintenance even if your mechanic recommends one, you likely won’t need another as long as you take care of the engine.



Nelson Xavier Ssenyange

Team Leader

Germax Auto Spares & Garage

Lukade Road, Naalya



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