Why Is Engine Sludge Harmful for Your Vehicle?

Your vehicle’s engine oil can turn into thick oil sludge when it isn’t replaced regularly. When this happens, the lubricating, cooling, and cleaning functions of motor oil will be lost.

What Causes Sludge to Form In the Engine?

Soot, acids, dirt, water, fuel, and other combustion byproducts accumulate in engine oil over time. Engine oil isn’t a stable compound, which means it oxidizes when it’s exposed to the heat generated by your vehicle’s internal combustion engine.

During oxidation, engine oil molecules degrade and mix with dirt, gasoline, metallic particles, water, gases, and coolant. This creates organic acids and high-molecular-weight polymeric products that react further with one another and form sludge.

The sludge builds up on hot or cold metal surfaces like a thin film of lacquer or varnish. However, it eventually bakes into a harder substance that looks like tar. Sludge can be very difficult to remove.

Sludge Formation Due to Frequent Short Drives

Sludge formation is greatly exacerbated by frequent short drives where the engine is started and then shut down before it has the chance to warm up completely. The reason for this is that for every gallon of fuel a gasoline engine burns, it produces a gallon of water as a byproduct, and some of that water vapor always bypasses the piston rings and enters the crankcase.

Sludge formation is greatly exacerbated by frequent short drives where the engine is started and then shut down before it has the chance to warm up completely. The reason for this is that for every gallon of fuel a gasoline engine burns, it produces a gallon of water as a byproduct, and some of that water vapor always bypasses the piston rings and enters the crankcase.

–Richard McCuistian, ASE Certified Master Automobile Technician

When the engine is allowed to warm up sufficiently, the PCV system (if it’s not clogged or disconnected) will totally eliminate the water vapor. If the engine is running too cool or isn’t allowed to warm up because of frequent short trips (a mile or less), the water vapor condenses in the crankcase, mixes with the oil, and forms ugly black sludge that looks like tar. However, there are other factors related to extended oil change intervals.

What Are the Effects of Sludge On an Engine?

Engine sludge retains more heat, resulting in a hotter engine and making the radiator and cooling system work harder. Additionally, engine sludge can block oil passages inside your engine, depriving certain engine components of the oil. As a result, these components won’t receive the oil’s lubricating, cooling, and cleaning effects.

If ignored, engine sludge can cause a wide range of issues, including power loss, excessive fuel consumption, oil pressure problems, hard starting, and engine blow-by. It can also cause your vehicle to overheat, which can worsen and severely damage your engine. Essentially, sludge buildup can damage and even cripple your engine.

Personal experience from Richard McCuistian, ASE Certified Master Automobile Technician: A “mom and pop” car that hasn’t been driven very much or very far might look like a cream puff inside and out, and yet have a lot of sludge in the engine due to short drives. One man bought a 1993 Acura with very low miles that had belonged to an older couple, and the following week, he made a 300 mile round trip. The sludge that caked the inside of the engine melted away, collected in the engine oil pan, clogged the oil pump pickup screen, and destroyed the engine. He couldn’t blame the older couple because they had no idea they had created so much sludge with all those short drives.

How to Prevent Engine Oil From Becoming Sludge

There are several practices that you should do to protect your engine from sludge. These include the following:

Always Warm the Engine Completely Before Turning it Off

In addition to always warming the engine sufficiently, make sure the engine isn’t running too cold because of a bad thermostat that is stuck open or opens too soon.

Regularly Change Oil and Oil Filter

Frequently flushing old oil and replacing your engine’s oil and oil filter is one of the best ways to prevent it from turning into sludge. Make sure to keep an eye on your vehicle’s check engine or oil check light, because they can be signs that your vehicle needs an oil change. Remember that vehicles require oil every five to ten thousand miles, depending on your vehicle and the type of oil used.

Avoid Driving In Harsh Conditions

Driving frequently in stop-and-go conditions and operating in excessively hot or cold weather can increase the likelihood of sludge buildup.

Lessen Short Trips

Again, short commutes cause the engine to operate at lower temperatures, which might result in sludge buildup. Furthermore, shorter trips do not allow the engine enough time to achieve its optimal operating temperature, which can also lead to sludge formation.

Prevent Overheating

When oil is kept at high temperatures for an extended period of time, oxidation can occur more rapidly. In fact, every time the temperature increases by 18°F, the oil’s oxidation rate doubles. So, keeping an eye on your vehicle’s temperature gauge and preventing scenarios where your vehicle runs hot can prevent sludge formation.

Use Synthetic Engine Oil

Conventional engine oil (also known as mineral oil) is more volatile than synthetic engine oil. Synthetic base oils oxidize slower because they’re more thermally stable. Synthetic engine oil also has additives, such as detergents and dispersants, that help reduce the rate of degradation. As a result, an engine filled with synthetic motor oil can drive more miles before needing another oil change.

If your vehicle has sludge in its engine, then an engine flush is the easiest way to get rid of it. This is a method where an engine flush solution is added to the oil and the engine is left to idle for five to ten minutes. Regardless, you shouldn’t wait until your engine reaches the point where it has so much sludge that an engine flush is needed. Keep an eye on your engine’s performance and stay on top of your vehicle’s oil change schedule.