Primary Functions of Motor Oil: Engine Oil Characteristics

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Questions and Answers

What is the primary purpose of using oil cooled pistons in some engines?

To increase power output and reduce oil contamination

To transfer heat from the pistons to the oil (correct)

To act as a sealant between the piston rings and cylinder liner walls

To prevent metal-to-metal contact between bearing surfaces

Which characteristic of engine oil is most important in determining the appropriate oil to use for a specific engine application?

Viscosity (correct)

Additive package

Detergency

Lubricity

How does high viscosity oil affect engine performance compared to low viscosity oil?

High viscosity oil reduces fluid friction, improving engine performance

High viscosity oil has no impact on engine performance

High viscosity oil increases fluid friction, reducing engine performance (correct)

High viscosity oil only affects performance in engines operating at high temperatures

What is the primary function of the oil film between bearing surfaces in an engine?

To reduce friction and wear Signup and view all the answers

Which of the following is the primary reason that engine oil must be matched to the specific engine and operating conditions?

To maintain oil service life Signup and view all the answers

What is the primary purpose of the Society of Automotive Engineers (SAE) viscosity numbering system for engine oils?

To specify the appropriate oil viscosity for different engine applications Signup and view all the answers

How does low viscosity oil affect the oil film between bearing surfaces compared to high viscosity oil?

Low viscosity oil maintains a thinner oil film, which is more easily squeezed out under high loads Signup and view all the answers

What is the primary function of oil cooled pistons in some engines?

To transfer heat from the pistons to the oil Signup and view all the answers

How does the viscosity of engine oil affect engine performance?

Higher viscosity oil reduces engine performance by increasing fluid friction Signup and view all the answers

What is the primary purpose of the oil film between bearing surfaces in an engine?

To reduce friction and wear Signup and view all the answers

Which of the following is NOT a function of engine oil?

Providing compression for combustion Signup and view all the answers

What is the primary reason that engines can operate for long service intervals?

The use of high-quality lubricants Signup and view all the answers

What is the purpose of changing engine oil?

To remove harmful debris collected by the oil Signup and view all the answers

According to the information provided, what is true about engine operating clearances?

They have decreased as advances in manufacturing technology have increased Signup and view all the answers

What is the primary reason for the rough appearance of machined engine surfaces when viewed under a microscope?

No machining process can produce a perfectly smooth surface Signup and view all the answers

Which of the following statements is true about the oil film provided by engine oil?

It reduces both friction and component wear Signup and view all the answers

What is the purpose of CH-4 oils?

To meet 1998 exhaust emission standards Signup and view all the answers

Why are synthetic oils becoming more common according to the text?

To decrease engine drag during cold weather starting Signup and view all the answers

What is a key reason for consulting engine and oil technical service representatives?

To address speed, load, altitude, and temperature-related issues Signup and view all the answers

Why should the vehicle work bay be isolated from other shop work bays during lube, oil, and filter service?

To prevent contamination of the engine oil system by airborne contaminants Signup and view all the answers

What is a primary cause of most bearing failures mentioned in the text?

Dirt contamination in the lubricant Signup and view all the answers

Why should transfer mechanisms like hoses and funnels be kept very clean as per the text?

To prevent dirt and dust contamination during non-service intervals Signup and view all the answers

What is one of the main reasons for containing oil spills and maintaining cleanliness in the service bay?

To reduce airborne contaminants entering the engine system Signup and view all the answers

Why should used oil transfer mechanisms never be used to supply new oil according to the text?

To maintain a clean and uncontaminated supply of new oil Signup and view all the answers

What is the purpose of oxidation inhibitors in engine oil?

To prevent excess oxygen absorption and reduce varnish buildup Signup and view all the answers

Which additive helps to lower the pour point of oil?

Pour point additives Signup and view all the answers

What is the purpose of anti-rust agents in engine oil?

To maintain an oil film on metal surfaces to prevent rust Signup and view all the answers

Which API service category is meant for 2010 and older automotive engines?

SM Signup and view all the answers

What is the purpose of metal deactivators in engine oil?

To prevent metal deterioration as oxidation occurs in the oil Signup and view all the answers

What does the CJ-4 API service category describe?

Oils for high-speed four-stroke cycle diesel engines meeting 2010 standards Signup and view all the answers

'Film strength additives' in engine oil serve to:

Maintain the oil film between bearing surfaces Signup and view all the answers

"What is the main function of foam inhibitors in engine oil?"

"Limit creation of air bubbles in the oil" Signup and view all the answers

"What do anti-rust agents help prevent when an engine is not operating?"

"General corrosion on internal engine parts" Signup and view all the answers

What is the primary function of multi-viscosity oils like 10W/30?

To reduce fluid friction during cold starts and maintain adequate oil film at high temperatures Signup and view all the answers

What does the term 'viscosity index' refer to?

The rate at which oil changes viscosity as temperature changes Signup and view all the answers

What is the primary purpose of pour point testing?

To determine the lowest temperature at which the oil can flow Signup and view all the answers

Why are oil additives added to engine oils?

To address specific problems that oils may encounter during engine operation Signup and view all the answers

What is the primary function of detergents in engine oils?

To prevent deposits from forming on internal engine parts Signup and view all the answers

What is the primary role of dispersants in engine oils?

To keep deposits suspended in the oil Signup and view all the answers

What can happen if piston rings become stuck in the pistons?

Smoky exhaust, power loss, and oil contamination Signup and view all the answers

How do detergents and dispersants work together to keep the engine clean?

Detergents prevent deposits, and dispersants keep particles suspended for removal Signup and view all the answers

What factor must be considered when selecting engine oils for an engine?

The quality and chemical composition of the fuel supply Signup and view all the answers

What can happen if unburned fuel enters the oil as a byproduct of combustion?

It can result in sulfuric acid formation in the oil Signup and view all the answers

Study Notes

Engine Oil Characteristics

Viscosity is a measure of an oil's resistance to flow, with higher viscosity oils flowing more slowly and lower viscosity oils flowing more quickly.
Thicker oils have higher viscosity and are able to maintain an oil film between bearing surfaces, but can also increase fluid friction and reduce engine performance.
Lower viscosity oils flow more easily and can reduce fluid friction, but may not provide an adequate oil film under high loads.

Functions of Engine Oil

Reduces wear between moving parts by providing a consistent oil film between mating surfaces.
Cleans the engine by carrying dirt, water, acids, and combustion by-products away from bearing surfaces.
Absorbs heat generated within the engine.

Oil Classifications

The American Petroleum Institute (API) classifies oils according to their performance characteristics.
There are two main types of oil classifications: SI (spark ignition) for gasoline engines and CI (compression ignition) for diesel engines.
API service categories include SN, SM, SL, and SJ for gasoline engines, and CJ-4 and CI-4 for diesel engines.

Oil Additives

Oxidation inhibitors prevent the oil from absorbing excess oxygen and reduce the buildup of varnish and sludge.
Anti-rust agents help maintain an oil film on internal engine parts when the engine is not operating, preventing rust formation.
Viscosity index improvers reduce the rate of viscosity change with temperature changes.
Film strength additives help maintain the oil film between bearing surfaces under severe operating conditions.
Foam inhibitors limit the creation of air bubbles in the oil.

Storage and Handling

The vehicle work bay used for lube, oil, and filter service should be isolated from the rest of the shop to prevent airborne contaminants from entering the engine oil system.
The service bay environment must be kept clean, and technicians should take precautions to prevent dirt and dust contamination during service.
Oil reservoirs should be positioned to prevent oil spills and ensure containment.
Used oils should be collected in suitable containers and transferred to recycling containers using separate mechanisms to prevent cross-contamination.

Oil Viscosity

Oil viscosity can change with temperature changes.
Multi-viscosity oils, such as 5W/20, 10W/30, or 15W/40, enable a single oil to be used over a wide range of operating temperatures.
Viscosity index (VI) refers to the rate of viscosity change with temperature changes.
Oils with a high viscosity index (e.g. 100) are more stable and maintain their viscosity over a range of temperatures.
Pour point is the lowest temperature at which an oil can be poured under prescribed test conditions.

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Description

Learn about the functions and characteristics of engine oil in maintaining engine components. Explore how engine components are manufactured and the impact of manufacturing technology on engine operating clearances. Understand the importance of engine oil in reducing friction and wear.

Engine Oil Functions and Characteristics

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