![]() ![]() Viscosity index also plays a crucial role when temperatures are known to fluctuate widely. At the highest temperature extreme, the viscosity must not be so low that surfaces are allowed to rub and collide, resulting in excavated working surfaces and failure. At the lowest temperature extreme, the oil must be fluid enough to enable movement and flow. Usually extreme temperatures are considered first and then normal operating temperatures. Starts, stops, coast-downs, slow speeds and reverse-direction part movements are all oil film/viscosity starvation events. This is why it’s often said that each time you start your car or truck, you are causing mechanical wear equivalent to 500 miles of driving. ![]() Without speed, oil films are not producible. These oil films build a clearance between working surfaces to mitigate friction and wear from mechanical contact. Both define the viscosity needed to produce hydrodynamic and elastohydrodynamic oil films. Speed is an important factor, as is load. Lubrication engineers consider numerous factors when matching viscosity selection to the needs of the machine. Viscosity Starvation in Worst-case Scenarios Low viscosity equates to small molecules that are more prone to vaporization at high temperatures along the piston ring belt, cylinder wall and exhaust valves. Too low viscosity can also lead to excessive volatilization and oil consumption in engines, both of which have a negative environmental impact. Excessive wear in the combustion chamber region (rings, cylinder wall, valves and cams/followers) caused by aggressively low viscosity and worst-case scenarios will result in the loss of combustion efficiency, higher fuel consumption and harmful gases being released out the tailpipe. Such scenarios in a car engine may occur due to low coolant levels, heavy loads (pulling a trailer), hot ambient temperatures, low oil levels, driving on dirt roads (high particle ingestion), short-trip driving patterns, water contamination and fuel dilution. However, in worst-case scenarios, dangerously collapsed oil films can accelerate wear and lead to premature failure. ![]() Under ideal conditions, lowering viscosity in an engine may result in no harm. While any effort to decrease energy consumption and protect the environment is a noble cause, you should be wise to how excessive viscosity trimming can backfire. Of course, the primary driver for energy conservation is not to save money on fuel or electricity but rather to reduce the consumption of fossil fuels, which emit harmful gases (carbon dioxide, nitric oxides, hydrocarbons, etc.) into the atmosphere as a byproduct of combustion. These changes are all for the sake of energy conservation. In recent years, we’ve seen automaker-specified viscosity being lowered in crankcase service from 5W40 to 5W30, and now in some cases to 5W20. One of the most famous disadvantages of too much viscosity is high energy consumption. It can also impede lubricant movement and flow to lubricant-hungry surfaces. For instance, too much viscosity can cause churning losses and excessive heat generation from molecular friction. Like most things, the selection of a lubricant’s viscosity must be optimized to enable needed protection and disable the danger from excessive viscosity. There is also a well-known penalty and reliability risk from too much viscosity. Without viscosity, most machines would rapidly self-destruct with mechanical friction and wear. Sometimes that clearance is thick and bountiful, and other times it is deflated or extinct. The oil’s viscosity bears the load and defines the extent of clearance achieved between working surfaces. s 1 cP = 0.Industry rides on a film of oil.Relationship between pascal-second to poise:ġ0 P = 1 kg Once the value of K is known, the viscosity can be determined by measuring the amount of time the test liquid flows between the two graduated marks.ġ Pascal-second (Pa Where \(K\) is the value of a liquid with known viscosity and density such as water. ![]()
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