What are Engine oil contaminants


What are engine oil contaminants?

Contaminants! These are those forces of evil that can turn a perfectly untarnished engine into a piece of junk. These include air, water, fuel, soot deposits, metal debris etc., that wreak havoc on the engine. Engine oil is added to the engine to lubricate it and minimise the effect of these contaminants. The engine oil absorbs these contaminants and prevents them from reaching the engine.

Let us understand more about these contaminants, their types and how they affect the engine and engine oil.


Abrasives include dust & dirt particles, and metal pieces from the engine.

  • Dust/dirt –  Dust/dirt enters the engine through leaks in the air intake system, seals, ventilation system, and a contaminated oil supply.
  • Metal pieces – These are wear particles that get generated when the engine parts rub against each other.

Abrasives are the most dangerous and damaging of all the contaminants. If left unchecked, abrasives can cause irreparable engine and component wear resulting in reduced vehicle reliability and increased maintenance cost. But the damage is not limited to the engine alone. These abrasives are harsh enough to deplete and deteriorate engine oil too.

car engine

Combustion By-Products

No matter how good the engine is, it never burns all the fuel completely. This incomplete combustion produces numerous byproducts such as water, acids and soot.

  • Water:  Water ingression is caused by bad seals, system vents, broken cooling lines, environment and condensation. Water deposits on the cylinder walls and enters the crankcase, where it leads to sludge and corrosion. Water contamination reduces the lubrication capacity of the oil and leads to component wear.
  • Acids: When water combines with blowby gases, acids are formed that degrade the pistons, rings and liners.
  • Soot: All engines produced some degree of soot. It is produced when the burning fuel mixes with oil and consists of tiny pieces of elemental carbon. When this soot manages to migrate into your crankcase, it mixes with the oil. This mixing lowers the oil’s viscosity, negatively affects oil pressure and forms sludge and other deposits.

Fuel Dilution 

Fuel dilution occurs when the fuel slips in the crankcase and mixes with engine oil. The most common causes for this slippage include clogged air filters, engine blowby, faulty injectors, rupture of fuel lines and fuel pump failure. When a large quantity of fuel mixes with oil, the oil loses its viscosity and thickness. As a result, the oil loses efficiency and fails to protect/lubricate the engine parts like the cylinder, pistons, and rings.

Engine coolant


Engine coolant often finds its way into oil through cracked cylinder heads, blown head gaskets, defective seals, cracked manifolds, and corrosion-related engine damage. When the coolant mixes with the oil, its viscosity increases, and the oil thickens into a sludge. As a result, the oil filter may clog up, and the oil pump may struggle to maintain ideal oil pressure. The blend of engine oil and coolant also produces an intermediary substance known as ‘oil balls’. These are abrasive substances that erode the delicate metal parts of the engine.

heat sources


Two heat sources affect the engine oil: Internal heat generated by the engine and external heat from the surroundings. When the engine heats up beyond a certain temperature threshold, the oil reacts with heat, i.e., there is a thermal breakdown. In a thermal breakdown, engine oil chemically reacts with the heat and loses its viscosity (thinning of the oil). Heat also causes the depletion of oil additives and creates deposits on the intake valves. All this results in reduced performance of the engine oil and damage to the engine.

The prolonged presence of the contaminants in the oil makes it lose its sheen and effectiveness; it becomes thick, slimy, dark and dry. Effective oil management and maintenance is key to minimising the effect of these contaminants and making your vehicle run its course. Effective oil management includes: selecting the best engine oil with recommended oil grade, maintaining recommended oil change intervals, periodic checking for oil level, choosing the right engine oil filter and timely cleaning/replacement of oil filter.

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