Viscosity

What would be the normal viscosity range for an engine oil at operating temperature?

10 to 15 centistokes at normal operating temperature

What would be the normal viscosity range for roller bearing oil at operating temperature?

10 to 300 centistokes at normal operating temperature.

What would be the normal viscosity range for hydraulic oil at operating temperature?

20 to 100 centistokes at normal operating temperature.

What percentage increase in viscosity does each ISO viscosity grade have over the one just below?

50%

What is considered to be the maximum viscosity limit for hydraulic vane pumps at startup temperature?

860 centistokes

Kinematic viscosity is measured using a capillary gravity flow viscometer or a rotating spindle viscometer?

A capillary viscometer

What property of oil measures an oil's internal resistance to flow and shear?

Absolute (or dynamic) viscosity

Name a major factor in determining the correct oil viscosity for a rolling element bearing.

Bearing speed factor (also known as DN factor) where rotational speed (RPM) is multiplied by pitch diameter in millimeters.

List three fluid qualities typically required by hydraulic systems.

Correct viscosity, oxidation stability, antifoam and air separation, high viscosity index, wear protection, rust protection, machine compatibility.

How can heat permanently reduce oil's viscosity?

Cracking

A base number will typically increase or decrease as the oil ages?

Decrease

How can heat permanently increase oil's viscosity?

Evaporative losses, oxidation

Mineral oils cannot have a viscosity index higher than 100. True or False?

False. Highly refined mineral oils may have VI as high as 130.

When two surfaces are separated by a lubricant, what friction, if any, remains?

Fluid or internal friction remains. It is a measure of the fluid's internal resistance to flow or viscosity.

If an automotive engine or gear oil is designed to meet more than one SAE viscosity limit, what is it commonly called?

Multigrade, for example- SAE 10W-40, SAE 15W-40, SAE 5W-50, etc.

If a mineral oil has a viscosity index of 100, will the base oil come from paraffinic or naphthenic crude oils?

Paraffinic

Which mineral oil has the higher natural viscosity index, paraffinic or naphthenic?

Paraffinic oils have higher natural VI than naphthenic oils.

Oils are often quoted as having a "Pour Point". What is this?

Pour point is the lowest temperature at which a liquid lubricant will flow. This is useful when considering lubrication under conditions of low temperature or refrigeration applications.

When a SAE 20 is blended with a SAE 40, will the resulted viscosity be closer to SAE 30 or SAE 60?

SAE 30

Of the following motor oils, which oil is best suited for cold start conditions? -SAE 15W-50 -SAE 40 -SAE 20 -SAE OW-30

SAE OW-30

In selecting lubricating oil for a particular application, what stages would normally be followed?

Selection of base oil, choose oil viscosity, define boundary lubrication requirements, other required properties and additives.

If an automotive engine or gear oil is designed to meet only one SAE viscosity limit, what is it commonly called?

Single or monograde, for example- SAE 30, SAE 40, etc.

What factors influence the choice of viscosity?

Speed (RPM), load, open or closed, oil feed, bearing size.

Compared to an oil with a VI equal to 100, if an oil has a viscosity index of 0, how will its viscosity change with temperature?

Such oil viscosity would change more rapidly with changes in temperature, compared to an oil with a VI equal to 100.

Hydrodynamic lubrication produces greater oil film thickness than EHD. True or False?

True

The viscosity of SAE 50 engine oil is similar to that of SAE 90 gear oil at the same temperature. True or False?

True

The viscosity of SAE 90 gear oil is similar to that of ISO 220 oil at the same temperature. True or False?

True

Abbreviations VHVI and UHVI are often used in connection with lubrication oils. What do they mean?

VHVI= Very High Viscosity Index, such as 130 UHVI=Ultra-High Viscosity Index, such as 150

An oil with a viscosity index of 135 is likely a VI improved mineral oil or a straight grade oil?

VI Improved

What is the term used to define the measure of a fluid's internal resistance to flow?

Viscosity

What properties of oil are used to calculate viscosity index?

Viscosity Index is calculated from an oil's kinematic viscosity at both 40 C and 100 C.

The term "Viscosity Index Improver" (or VII) is often used in connection with lubricating oils. What does this mean?

Viscosity index can be improved by dissolving a polymeric material in the oil. Multigrade oils generally contain this.

If high pressure were applied to a lubricant, what would be its effect on viscosity?

Viscosity would increase

In the SAE crankcase viscosity classification OW-30, what does the W stand for?

Winter

Name two possible causes of viscosity loss.

Fuel dilution in engine oils, top-up with lighter oil, permanent shear of viscosity index improver.

Name three contaminants that can reduce oil viscosity.

Fuel, solvents, refrigerant

Is the viscosity designated by 80W-140 is associated with crankcase oils or driveline gear oils?

Gear oils

When oil is momentarily heated, how will its viscosity change?

Go down

Larger (heavier) oil molecules are associated with high or low viscosity?

High

Theoretically, high viscosity index oils are needed only under what conditions?

High VI oils are generally required where machines are likely to operate over a wide range of temperatures, such as outdoors.

When a full film of lubricant exists between mating surfaces, what is this condition called?

Hydrodynamic lubrication

What is the ISO viscosity grade that sequentially follows ISO VG 320?

ISO VG 460

How does a viscosity index improver work?

In COLD oil, the VII molecules adopt a coiled shape and have little effect on viscosity. In HOT oil, the VII molecules uncoil and have a thickening effect.

What is a common cause of seal swell or seal shrinkage?

Incompatibility with base oils and/or additives

Flash point increases or decreases as oil viscosity increases?

Increases

How does glycol contamination affect oil viscosity?

Increases it

How does soot in diesel engine oil affect oil viscosity?

Increases it

What effect does emulsified water have on oil viscosity?

Increases it

When an oil oxidizes, how does its viscosity typically change?

It goes up

Define Viscosity Index

It is the rate of change in viscosity with respect to the change in temperature.

Viscosity can be measured in a number of different ways. Name three of them.

Kinematic viscosity, dynamic viscosity, Redwood viscosity, Saybolt viscosity, Engler viscosity.

Define viscosity

Measure of the resistance to flow (or shear) of a fluid (internal friction).