CHAPTER 16 LUBRICATION SYSTEM OPERATION AND DIAGNOSIS
OBJECTIVES After studying Chapter 16, the reader should be able to: • Prepare for ASE Engine Repair (A1) certification test content area “D” (Lubrication and Cooling Systems Diagnosis and Repair). • Explain hydrodynamic lubrication. • Describe how the oil pump and engine lubrication work. • Discuss how oil flows to the valve train components. • Explain how to inspect an oil pump for wear.
Boundary lubrication Cavitate Dry sump Gallery Gerotor Hydrodynamic lubrication Positive displacement pumps Pressure regulating valve Sump Wet sump Windage tray KEY TERMS
INTRODUCTION • Engine oil is the lifeblood of any engine. The purposes of a lubrication system include the following: • Lubricating all moving parts to prevent wear • Helping to cool the engine • Helping to seal piston rings • Cleaning, and holding dirt in suspension in the oil until it can be drained from the engine • Neutralizing acids that are formed as the result of the combustion process • Reducing friction • Preventing rust and corrosion
FIGURE 16–1 Oil molecules cling to metal surfaces but easily slide against each other. LUBRICATION PRINCIPLESPURPOSE AND FUNCTION • Lubrication between two moving surfaces results from an oil film that separates the surfaces and supports the load.
FIGURE 16–2 Wedge-shaped oil film developed below a moving block. LUBRICATION PRINCIPLESPURPOSE AND FUNCTION
FIGURE 16–3 Wedge-shaped oil film curved around a bearing journal. LUBRICATION PRINCIPLESHYDRODYNAMIC LUBRICATION • This wedging action is called hydrodynamic lubrication, and depends on the force applied to the rate of speed between the objects and the thickness of the oil.
FIGURE 16–4 The dash oil pressure gauge may be a good indicator of engine oil pressure. If there is any concern about the oil pressure, always use a mechanical gauge to be sure. ENGINE LUBRICATION SYSTEMS • PURPOSE AND FUNCTION • NORMAL OIL PRESSURE • OIL TEMPERATURE
OIL PUMPS • PURPOSE AND FUNCTION • PARTS AND OPERATION • TYPES OF OIL PUMPS • External gear type • Internal/external gear type • Rotor type • Gerotor type
FIGURE 16–6 In an external gear-type oil pump, the oil flows through the pump around the outside of each gear. This is an example of a positive displacement pump, wherein everything entering the pump must leave the pump. OIL PUMPS
FIGURE 16–7 A typical internal/external oil pump mounted in the front cover of the engine that is driven by the crankshaft. OIL PUMPS
FIGURE 16–9 Gerotor-type oil pump driven by the crankshaft. OIL PUMPS
OIL PUMPS • OIL PRESSURE REGULATION • FACTORS AFFECTING OIL PRESSURE • Leaks • Oil pump capacity • Viscosity of the engine oil • OIL PUMP CHECKS • Visual inspection • Measurements
FIGURE 16–10 Oil pressure relief valves are spring loaded. The stronger the spring tension, the higher the oil pressure. OIL PUMPS
FIGURE 16–11 A typical engine design that uses both pressure and splash lubrication. Oil travels under pressure through the galleries (passages) to reach the top of the engine. Other parts are lubricated as the oil flows back down into the oil pan or is splashed onto parts. OIL PUMPS
FIGURE 16–12 (a) A visual inspection indicated that this pump cover was worn. (b) An embedded particle of something was found on one of the gears, making this pump worthless except for scrap metal. OIL PUMPS
FIGURE 16–13 (a) The oil pump is the only part in an engine that gets unfiltered engine oil. The oil is drawn up from the bottom of the oil pan and is pressurized before flowing to the oil filter. (b) If debris gets into an oil pump, the drive or distributor shaft can twist and/or break. When this occurs, the engine will lose all oil pressure. OIL PUMPS
Is a High-Pressure or High-Volume Oil Pump Needed? • No. Engine parts need pressure after the oil reaches the parts that are to be lubricated. The oil film between the parts is developed and maintained by hydrodynamic lubrication. Excessive oil pressure requires more horsepower and provides no better lubrication than the minimum effective pressure. A high-volume pump is physically larger and pumps more oil with each revolution. A high-volume pump is used mostly in race engines where the main and rod bearing clearances are much greater than normal and therefore would need a great volume of oil to make up for the oil leaking from the wide clearances.
OIL PASSAGESPURPOSE AND FUNCTION • Oil from the oil pump first flows through the oil filter then goes through a drilled hole that intersects with a drilled main oil gallery, or longitudinal header. • This is a long hole drilled from the front of the block to the back. • Inline engines use one oil gallery. • V-type engines may use two or three galleries.
FIGURE 16–14 An intermediate shaft drives the oil pump on this overhead camshaft engine. Note the main gallery and other drilled passages in the block and cylinder head. OIL PASSAGESPURPOSE AND FUNCTION
FIGURE 16–15 Oil is sent to the rocker arms on this Chevrolet V-8 engine through the hollow pushrods. The oil returns to the oil pan through the oil drainback holes in the cylinder head. OIL PASSAGESVALVE TRAIN LUBRICATION
The New Hemi Engine Oiling System • The Chrysler Hemi V-8 engine uses a unique oiling system because the valve lifters are fed oil from the top of the cylinder heads and through the pushrods. While it is normal to have oil flowing through hollow pushrods, it is unique that in the Hemi V-8 the oil flows backward from normal and from the head down the hollow pushrods to the lifters. Be sure to use the specified viscosity of oil, as this is critical for proper lubrication of the valve lifters.
FIGURE 16–16 A typical oil pan with a built-in windage tray used to keep oil from being churned up by the rotating crankshaft. OIL PANSPURPOSE AND FUNCTION • The oil pan is where engine oil is used for lubricating the engine. • Another name for the oil pan is a sump.
Why Is It Called a Windage Tray? • A windage tray is a plate or baffle installed under the crankshaft and is used to help prevent aeration of the oil. Where does the wind come from? Pistons push air down into the crankcase as they move from top dead center to bottom dead center. The pistons also draw air and oil upward when moving from bottom dead center to top dead center. At high engine speeds, this causes a great deal of airflow, which can easily aerate the oil. Therefore, a windage tray is used to help prevent this movement of air (wind) from affecting the oil in the pan. Try the following: • Take an oil pan and add a few quarts (liters) of oil. • Then take an electric hair dryer and use it to blow air into the oil pan. • Oil will be thrown everywhere, which helps illustrate why windage trays are used in all newer engines.
FIGURE 16–17 A dry sump system as used in a Chevrolet Corvette. DRY SUMP SYSTEM • CONSTRUCTION AND OPERATION • ADVANTAGES • DISADVANTAGES
OIL COOLERS • Coolant flows through the oil cooler to help warm the oil when the engine is cold and cool the oil when the engine is hot. • Oil temperature should be: • Above 212°F (100°C) to boil off any accumulated moisture • Below 280°F to 300°F (138°C to 148°C)
FIGURE 16–18 Oil is cooled by the flow of coolant through the oil filter adaptor. OIL COOLERS
What Is Acceptable Oil Consumption? • There are a number of opinions regarding what is acceptable oil consumption. Most vehicle owners do not want their engine to use any oil between oil changes even if they do not change it more often than every 7,500 miles (12,000 km). Engineers have improved machining operations and piston ring designs to help eliminate oil consumption. • Many stationary or industrial engines are not driven on the road, so they do not accumulate miles but still may consume excessive oil. • A general rule for “acceptable” oil consumption is that it should be about 0.002 to 0.004 pound per horsepower per hour. • Generally, oil consumption that is greater than 1 quart for every 600 miles (1 liter per 1,000 km) is considered to be excessive with a motor vehicle.
SUMMARY • Viscosity is the oil’s thickness or resistance to flow. • Normal engine oil pump pressure ranges from 10 to 60 PSI (200 to 400 kPa) or 10 PSI for every 1000 engine RPM. • Hydrodynamic oil pressure around engine bearings is usually over 1,000 PSI (6,900 kPa). • The oil pump is driven directly by the crankshaft or by a gear or shaft from the camshaft.
REVIEW QUESTIONS • What causes a wedge-shaped film to form in the oil? • What is hydrodynamic lubrication? • Explain why internal engine leakage affects oil pressure. • Describe how the oil flows from the oil pump, through the filter and main engine bearings, to the valve train. • What is the purpose of a windage tray?
CHAPTER QUIZ 1. Normal oil pump pressure in an engine is ________ PSI. • 3 to 7 • 10 to 60 • 100 to 150 • 180 to 210
CHAPTER QUIZ 2. Two technicians are discussing oil pumps. Technician A says that many oil pumps are driven directly off the front of the crankshaft. Technician B says that some are driven from the distributor if the engine uses a distributor-type ignition system. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B
CHAPTER QUIZ 3. A typical oil pump can pump how many gallons per minute? • 3 to 6 gallons • 6 to 10 gallons • 10 to 60 gallons • 50 to 100 gallons
CHAPTER QUIZ 4. In typical engine lubrication systems, what components are the last to receive oil and the first to suffer from a lack of oil or oil pressure? • Main bearings • Rod bearings • Valve train components • Oil filters
CHAPTER QUIZ 5. Hydrodynamic lubricants, created by the wedging action of oil between the crankshaft journal and the bearing, can be as high as ________ PSI. • 60 • 120 • 500 • 1,000
CHAPTER QUIZ 6. What type of oil pump is driven by the crankshaft? • Gerotor • Internal/external gear • External gear • Both a and b
CHAPTER QUIZ 7. Lower than specified oil pressure is measured on a high mileage engine. Technician A says that worn main or rod bearings could be the cause. Technician B says that a clogged oil pump pickup screen could be the cause. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B
CHAPTER QUIZ 8. Oil passages in an engine block are usually called ________. • Galleries • Holes • Runners • Pathways
CHAPTER QUIZ 9. Why is a dry sump system used in some high-performance vehicles? • It allows the vehicle to corner or brake for long periods • It allows the engine to develop more power • It allows for a greater oil capacity so that oil temperatures can be controlled • All of the above
CHAPTER QUIZ 10. Engine oil cooler uses what to cool the oil? • Coolant • Air • Air-conditioning evaporator output • Automatic transmission fluid after it flows through the radiator