Engine Oil Sludge

Engine Sludge


What is engine oil sludge?


Engine Oil Sludge

Engine oil sludge begins to develop when the lube oil starts to break down. Once it succumbs to shearing forces and other factors inside the engine, the lube oil thickens up, begins to solidify, and collects on the engine walls. Oil sludge is a thick gel formed when the engine oil is oxidized and contaminated. It is comprised of partially burnt fuel, metal fragments, and dirt. The motor oil then carries oil sludge, and you can find it sticking to the engine’s various moving parts. Thicker lube oil can no longer lubricate the engine, increasing metal-on-metal friction, which eventually speeds up the wear of the internal engine components. Without proper lubrication, you run the risk of overheating the engine or destroying the internals.

Engine sludge first accumulates on the top of the engine, in the oil pan, and in the valve cover section. Then, the oil sludge becomes thick due to high soot and sludge levels. The restriction causes reduced oil circulation, increases friction, and causes the engine to overheat. Abrasive soot will cause wear in tight tolerance areas such as fuel injector adjuster screws, adversely affecting fuel economy and engine performance. Soot causes oil thickening and increases engine wear, and sludge buildup causes oil filter plugging. A centrifuge for oil cleaning will capture and remove the soot and finer size contaminants from the lube oil. Additionally, bypass engine oil centrifuges can assist in sludge removal. 


What causes oil sludge?

Engine oil sludge is the result of a series of chemical reactions. As the lubricant degrades, it is exposed to oxygen and elevated temperatures. The higher the temperature, the more rapid the rate of degradation. For every 18°F (10°C) increase in temperature doubles the rate of oxidation. Oxidation of the lubricant oil will be accelerated considerably if catalytic particles are present in the oil. Copper wear particles are especially harmful, but ferrous particles and rust are active. The byproducts of this reaction form highly reactive compounds that further degrade the lubricant. Their byproducts react with other contaminants, forming organic acids and high-molecular-weight polymeric products. These products additionally react, forming the insoluble product known more commonly as sludge (organic contamination).

What begins as a thin film of lacquer or varnish builds up on hot or cold metal surfaces and bakes into an expensive mess. Furthermore, the lacquer and varnish oxidation products of the oil itself have an accelerating effect. Therefore, continuous lube oil cleaning is essential to keep the sludge content low.

Engine sludge does not appear out of the blue. Instead, engine sludge forms slowly and builds up over time. 

What causes engine sludge?

What causes engine sludge? Several different reasons cause engine oil sludge. These main causes of engine sludge include:

    • Using poor-quality lube oil
    • Ignoring lube oil service intervals
    • Oil contaminated by unburned fuel (This is more common in diesel engines than gasoline engines.)
    • Oil contaminated by the emissions systems
    • Environmental contaminants in the lube oil, like dust and other air-borne particulate matter and gases
    • Keeping the lube oil at extremely high temperatures for extended periods of time
    • Excessive engine idling time can contribute to excessive water in the crankcase oil, causing corrosion, sludge, and other problems. Excessive engine idling time can lead to injector fouling, piston and combustion chamber deposits, corrosive damage, and increased oil consumption.
    • Coolant contamination
    • Moisture contamination

Signs of Deterioration

If circulating oil of inferior quality is used, and the oxidative influence becomes grave, prompt action is necessary as the last stages in the deterioration will develop surprisingly quickly, within one or two weeks. In a severe case of oil deterioration, the system must be cleaned thoroughly and refilled with new oil.

Even if this seldom happens, it is wise to know the signs of deterioration. These may be some or all of the following:

    • Sludge precipitation in the centrifugal oil filter multiplies
    • The smell of oil becomes acrid or pungent
    • Machined surfaces in the crankcase become coffee-brown with a thin layer of lacquer
    • The paint in the crankcase peels off or blisters
    • Excessive carbon is formed in the piston cooling chamber


engine-sludge-contamination-removalForeign substances can significantly influence the type and rate of lubricant degradation. Metals such as iron and copper are catalysts for the degradation process. Contaminant-free lube oil (clean lubricating oil) is ideal, and monitoring the fluid’s contamination levels provides significant insight into the engine’s health.

It is highly recommended to use a centrifugal oil filter to prolong the lubricating oil lifetime and remove wear elements and contaminants from the lube oil. Centrifugal filters will reduce the carbon residue content and other solid contaminants from the lubricating oil. Centrifugal filters remove micron-size solids from the lube oil, such as engine sludge, wear debris, soot, dirt, carbonous material, and other contaminants. The oil and additives are still being decomposed by oxidation and nitration. The depletion of these additives will ultimately be the reason for the oil change. The IOW Group centrifugal filters can slow down the rate of this depletion, but they cannot eliminate it. Acids, fuel, and coolant are just a few of the contaminants that bypass filtration cannot address. They, too, can shorten the life of the lube oil. 


What are engine oil sludge symptoms?

Knowing the engine oil symptoms is very useful because you can tell if you have engine oil sludge or not. If the check engine light is on, this is a sign that the oil pressure sensor measured the oil pressure and detected abnormal processes. If the engine control panel reads high oil pressure, this is a sign that sludge is present in the engine oil, causing the oil pressure to rise. The oil passages are clogged up, and the engine is not lubricating properly. A common engine oil sludge symptom is thick engine oil. Is there oil sludge on the dipstick? Engine oil should not be sludgy. If the engine is overheating, this is a sign of poor oil flow and obstructions in the oil passageways. The engine oil lubricates the engine and dissipates the heat from the block. If the engine oil is stopped from flowing, the engine will overheat. Additionally, poor fuel economy and a noisy engine are symptoms of engine oil sludge. The engine will be very noisy if there is no proper lubrication. The metal-to-metal contact is imminent, along with the high heat that will be created. Eventually, the engine will either seize or spin a bearing.


How can you prevent engine oil sludge buildup?

The best recommendation we can give is better lube oil filtration and get regular oil changes and oil filter changes. Remove engine sludge before it becomes a problem. The most important thing you can do for your engine is to ensure you always follow the maintenance guidelines laid out in your owner’s manual. This is especially important for lube oil, or you risk serious and expensive engine damage.


Better Lube Oil Filtration

Better Lube Oil Filtration

Centrifugal filters remove organic contaminants and inorganic contaminants. The oil centrifuges reduce wear in the engine and significantly increase the engine’s life. Engine oil centrifuges can assist in sludge removal. Centrifugal filters are considered the most efficient and reliable form of filtration. Centrifugal filters are not disposable filters and are considered to be long-lasting, reliable, and durable products for effective lube oil filtration. They have a fast return on investment.

Not all centrifugal filters are created equal. The centrifugal filters manufactured by IOW Group are the only disc stack centrifuge filter on the market.

IOW Group centrifugal filters utilize centrifugal force to separate solids from a liquid phase. Drawing out solid particles from the lube oil to achieve a smoother operation of the engine by reducing wear on engine components. During the clarification process (liquids/solids separation), the cleaned oil moves toward the centrifuge bowl center and discharges through the outlet. The solid contaminants move toward the bowl periphery and collect on the centrifugal bowl wall. When cleaning the IOW centrifugal filters, you remove sludge deposits from inside the centrifuge bowl using a non-damaging wood spatula. 

When investing in a centrifugal filter, invest in the best on the market at contamination removal — the IOW Group centrifugal filters.


To learn more, visit our IOW Group Oil Centrifuges webpage or the IOW Group Oil Centrifuges website.
To learn more about oil degradation, visit our What is oil degradation? blog.
To learn more, read Machinery Lubrication’s article “Finding the Root Causes of Oil Degradation.”


Looking for a quote? Get started below!