Engine Oil

Engine Oil Analysis

Oil analysis was originally used to predict engine failures. However, it is still widely used today to ensure the reliability of engine systems. The majority of mobile equipment around the world, including locomotives, cars and mining equipment, trucks and agricultural equipment, oil and gas exploration and rigs, backup power generators and pipeline compression stations, are powered by reciprocating internal combustion engines.

Engine oil must be changed before it fails to perform the intended functions. However, frequent or early oil changes can have a high cost and impact the environment. The oil gradually becomes contaminated in rotating internal combustion engines. This can vary depending on age, load factor and environment. Engine oils contain additive packages that include alkaline components and detergents that neutralize the acids created by fuel combustion. The engine will not be protected adequately if the additive and oil combination is depleted. It is important to identify the type of oil contamination. This will allow you to make a better decision and take the necessary corrective actions. High levels of glycol contamination could indicate a cooling system leak.

Oil analysis provides information about the level of contamination and soil degradation status. This allows oil to change according to its condition, not when used. But what causes engine oil contamination?

Most Common Contaminants

A wide range of contaminants can be introduced to the oil during normal engine operation. Below are some of the most prevalent contaminants.

Combustion By-Products

Exhaust gases, or blowby gas, that leak through the valve guides, piston rings and turbocharger seals to the crankcase contain particles that can contaminate the oil with acids, carbon and partially burned fuels. Sulfur dioxides (SOx), which are common gases that react with sulfurous fuels like diesel, liquid fuel distillates, and heavy fuel oil, are also known as sulfur oxides. Natural gas-powered engines (LNG/CNG, propane) have more nitrous oxides (NO x). There will be different amounts of hydrocarbon oxidation (HCO x).

Acids and Varnish

If the lubricating oils come in contact with hot components of an engine, or if heated oils touch the entrapped oil, oxidation and degradation occur, creating contaminants like acids, sludge, and varnish.


These contaminants are generally caused by engine failure. An engine malfunction can cause fuel dilution. The stop-and-go operation, excessive engine idle, and other factors can cause viscosity losses. This can lead to severe wear and possible seizure. Fuel dilution can be caused by clogged filters, faulty injectors and fuel pump failure. However, it is possible for fuel lines to rupture, which could cause oil contamination.


Water vapour is a byproduct of combustion and reaches oil. The oil is not heated enough to boil the water off quickly with backup generators and low load engines. Acids are formed when water reacts with blowby gas. These acids degrade oil and corrode engine surfaces. Water ingress from the environment or broken cooling lines can cause rapid oil degradation and engine failure.


A large number of glycol-based engine coolants are used. Mixing coolant and oil can lead to leakage of head gasket seals, corrosion of cooling systems, or loss of integrity of cooling line fittings. Glycol is particularly corrosive to nonferrous bearing surfaces. Engine seizure can be caused by excessive coolant.


The mixture of oil and burning fuel on the cylinder liner(s) or delayed injection timing can cause soot to form. Injector and valve train wear can be caused by excessive soot. This can lead to an abnormal emission control system overload, resulting in fines.

What tests should be used to monitor engine oil? Every engine test must include tests to identify common contaminants and determine oil viscosity and wear metals.



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