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Engine oil background…

Thanks a lot to Jim Elkins of Jackmaster Oil Filters at who provided me with a lot of authoritative information on engine oil for this section based on his depth of experience and expertise in this area.

Engine oil lubricates the engine…

Engine oil is absolutely critical to the health of the engine.  It provides critically important lubrication between moving metal components inside the engine such as between the piston rings and the walls of the cylinders or between the crankshaft and the bearings in which it rotates.  In the context of the insides of an engine, the expression ‘wear and tear’ refers to, among other things, the loss of metal from engine components as a result of friction between them.

By acting as a buffer between the moving metal components, the engine oil ensures that these moving parts don’t readily come into direct contact with each other.  In this way, the engine oil minimises the loss of metal resulting from the friction between them.  This ensures that the exacting tolerances to which the components in the engine are manufactured are preserved and that the engine therefore continues to operate efficiently and quietly.

The wearing away of the exacting tolerances of engine components due to poor lubrication is what causes an engine to become noisy, because the components are allowed more room to move around and generate more noise as they bump against each other.  Engines with a minimum of wear are always quieter.

Engine oil assists in cooling the engine…

The engine oil also assists with the cooling of the engine by being another media in addition to the coolant through which heat can be transferred away from the engine components.  The source of this heat is the combustion of fuel in the combustion chambers above the pistons and also the friction between moving parts inside the engine.  The engine oil continually circulates throughout the engine via the sump (i.e. the lowest part of the engine) which, in turn, is cooled by air passing under the front of the vehicle while it’s being driven.

So, heat is transferred from the combustion chambers to the metal of the engine itself, then to the engine oil and to the sump which the engine oil travels through in a cycle.  This heat is then dissipated from the sump to the outside air which passes over it.  In this way, the engine oil assists in keeping the engine cool.

Engine oil cleans the engine…

An important role of the engine oil is to keep the insides of the engine clean from the contaminants that find their way into the insides of the engine by holding them in suspension within the oil.  It is exactly this necessary role of the engine oil that leads to it becoming depleted and which robs it of its protective lubricating properties because a lot of the contaminants that the oil holds are abrasive (e.g. metal particles).

You’ve probably noticed that the engine oil generally looks clear and clean on the dipstick shortly after it’s first poured into the engine during an oil change.  However, after a couple of months the engine oil darkens as a result of all the contaminants that have found their way into the oil.  Often when it’s drained out during an oil change, it’s pitch black.

Contaminants of engine oil…

The range of contaminants of the engine oil resulting from the operation of the vehicle are considerable and include the following:

Metal particles…

Tiny metal particles are deposited into the engine oil as a result of the friction between moving metal components inside the engine such as between the piston rings and the cylinder walls.  As components move against each other, microscopic metal particles sheer off in spite of the lubrication that the engine oil offers.  This tends to happen more when the engine RPMs (i.e. revolutions per minute) are higher.

If these metal particles are large enough and aren’t filtered out of the oil, they have the potential to cause damage to components such as the bearings in which the crankshaft and the camshaft rotate.  If they get stuck between the bearings and these rotating parts, they can wear grooves into the metal, grinding it away and wrecking the precision clearances between these parts in the process.  They can even become embedded in the surface of the bearings.

The minimum clearance between the bearings and the crankshaft in an engine is about 0.0254 millimetres (1/1000 inch).  This is the equivalent of about 25 microns, since one micron is equal to 1/1000 millimetres or 0.001 millimetres.  (The diameter of a human hair is about 40 to 120 microns.)  Any metal particle larger than about 25 microns that isn’t trapped by the oil filter has the potential to be stuck between a bearing and the crankshaft and cause excessive wear.  Metal particles smaller than about 25 microns remain suspended in the oil and can move between the bearings and the crankshaft without getting trapped between them.

However, other clearances in the engine are even smaller than 25 microns and can be as tiny as 5 microns.  Examples include the clearance between the piston rings and the cylinder walls, the clearance between the camshaft lobes and the valve lifters and the clearances between the components that make up the valve train.  These clearances are susceptible to wear from metal particles floating around in the engine oil that are smaller than 25 microns in size.

Atmospheric dirt or dust…

Atmospheric dirt or dust finds its way into the engine through the air intake.  The air intake allows air to enter the engine so that it can be mixed with fuel and then ignited and burned in the combustion chambers.  These are the particles that have escaped capture by the air filter, which enter the combustion chambers via the air intake and have been blown past the piston rings into the engine oil at the high pressures generated by the combustion of the fuel/air mixture.


Water is a by-product of the combustion of fuel and air.  A simplified chemical equation for the combustion of fuel and air is:

2C8H18 + 25O2 => 16CO2 + 18H2O + e

In words, this is:

Fuel (i.e. Iso-Octane) + Oxygen => Carbon Dioxide + Water + Energy

Water finds its way into the engine oil by being blown past the piston rings from the combustion chambers as a by-product of the combustion of the fuel/air mixture inside the combustion chambers.  Water also forms inside the engine by way of condensation.  When the engine is turned off and eventually cools, humidity in the air inside the engine condenses on the cold metal surfaces of the engine components as droplets of water, provided that the prevailing outside ambient temperature is low enough so that the engine becomes sufficiently cool.  Therefore more condensation occurs during the colder months of the year such as during winter.

Water is a menace to engine oil because it dilutes its ability to lubricate the engine components and because it has the ability to combine with other contaminants in the oil to form acids which are corrode the metal engine components, as well as non-metal seals and gaskets.

Of the air surrounding us that an engine sucks in for combustion, 78% is nitrogen.  During the combustion of the fuel/air mixture, this nitrogen combines with oxygen to form nitrogen dioxide, some of which finds its way into the engine by being blown past the piston rings from the combustion chambers.  Inside the engine, it can combine with water that is already in the oil to form nitric acid, which is a highly corrosive acid.  This acid has the ability to corrode the surfaces of metal engine components and to eat away at non-metal gaskets and seals inside the engine, increasing the likelihood of oil leaks.

Often there is sulphur in the fuel which is a by-product of the production process of fuel.  When this accumulates in the engine oil to any significant degree as a result of being blown past the piston rings, it can combine with water that is already in the oil to form sulphuric acid, which is also highly corrosive.


Carbon is a by-product of the incomplete combustion of fuel when there is insufficient oxygen in the fuel/air mixture to completely burn the fuel.  Carbon finds its way into the engine oil by being blown past the piston rings from the combustion chambers at the high pressures generated by the combustion of the fuel.

Carbon is an extremely absorbent element which depletes the engine oil of its chemical additives by absorbing them and therefore compromises the engine oil’s ability to do the things it was designed to such as providing lubrication and cleaning the insides of the engine.  (Some chemical additives in engine oil have properties which enhance the lubricating ability of the oil whereas others have detergent properties and have specifically been added to the engine oil to enable the engine oil to clean the insides of the engine while it operates.)


‘Sludge’ is the name given to the result of the chemical additives in engine oil decomposing and solidifying due to oxidation of the engine oil over time (i.e. chemical reaction with oxygen) as a result of the high temperatures that exist inside the engine.  These solids contaminate the engine oil and then coat themselves on the moving parts inside the engine as a form of varnish, which reduces the clearances between these parts and increases friction.

Types of engine oil filtration…

All in all, there is a considerable range of contaminants that the engine oil has to contend with.  Obviously the ideal would be to filter all of these contaminants out of the engine oil so that they can’t exacerbate wear inside the engine or impede the ability of the engine oil to protect the engine components.  While conventional engine oil filtration found on most production cars can only filter out a small portion of these contaminants, bypass oil engine filtration can filter out the overwhelming majority of all of them.

Amazingly, bypass engine oil filtration cleanses the engine oil of these contaminants on an ongoing basis so that the engine oil effectively remains as clean as it was when it was poured into the engine.  By removing all particulate contamination of the oil (e.g. metal particles) that causes engine wear, bypass filtration prevents virtually all engine wear from occurring.  Engine oil filtered in this way can then be used for 50,000 kilometres (30,000 miles) before being replacing with fresh oil, resulting in a dramatic saving of time (i.e. the hassle of getting the engine oil changed) and money (i.e. the cost of fresh engine oil and the cost of labour if you normally pay a mechanic to change the oil).

Further information on conventional engine oil filtration and bypass engine oil filtration can be found in the sections titled, Conventional Engine Oil Filtration, and, Bypass Engine Oil Filtration.

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Copyright 2016 Andrew Mackinnon.  All rights reserved.