Blog - Amsoil Dealer - Lowell

Viscosity you say, why does it matter?

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Viscosity is quite important when select the motor oil to use in your vehicle.  If you use a motor oil that has a viscosity that is too low or too high, in your engine may evoke a few problems. Problems such as decreased fuel economy, exaggerated chemical breakdown and increased wear become all too real issues.

What viscosity is and how it works.

As defined by the dictionary, viscosity is the property of a fluid that resists the force inclined to cause the fluid to flow. The higher the viscosity rating of an oil, the least likely it will readily flow from a container when it’s poured. As an example, honey has a higher viscosity than water and would flow much slower than water.


The numbers and letters such as 10W-40 dsecribes how the oil is designed to perform in a certain temperature. The 10W would tell you what its’ flow capacity in cold temperatures would be. The “W” means winter and would describe the oil’s flow capacity in cold weather. The lower the oil’s “W” viscosity, the more readily it will flow when it’s cold. The 40 describes the oil’s flow ability at 212ºF (normal operating temperature). A higher number indicates that it will remain thicker when the engine is hot and translates to better wear protection.


Now for the consequences

If you use an oil that has a viscosity rating that is too thin, it could possibly compromise the oils’ wear protection ability over time. The viscosity of an oil has a direct relationship on its’ ability to create a thin film of lubrication that will be sufficient to keep an engines metal parts from directly touching each other. Heat is an oils enemy and the hotter it gets the the thinner it will be, resulting in decreased wear and lubrication ability.


As the oil gets thinner, the result is insufficient oil pressure, which leads to variable valve timing systems malfunction in todays’ newer engines. Having low oil pressure could also lead to the lifters not contacting with the cam lobes properly, the result will be a knocking noise and increased wear.


If it is too thick the fuel economy will decrease. Thicker oil, makes it harder for the oil pump to distribute the oil properly throughout the engine. That in turn decreases the fuel economy. The oil also won’t be able to get to the engines’ essential sections at startup time as quickly as it is supposed to, initiating faster component wear.


In colder temperatures, if the oil is too it will impede your engine’s ability to start, resulting in a drained battery, and also possibly leaving you stranded. Oil that is too thick also won’t exhibit appropriate heat transfer from engine parts as it should. The increase in viscosity will also cause internal friction, and a higher operating temperature. The higher temperature will result in the oil oxidizing at a faster rate, and or chemically breaking down. What eventually happens is a build up of sludge that, that gets so bad over time, it will block oil passages leading to oil starvation in the engine and eventual engine failure.