LO 10-5 Identify and describe the types, functions, construction features, and applications of diesel engine lubrication system components

1. Components of Lubrication Systems

Components of Lubrication Systems

In addition to the oil itself, the lubrication system accomplishes its tasks through a number of major components, including:

• Oil pan
• Oil pump
• Pressure-regulating and pressure-relief valve
• Oil cooler
• Oil filter

1.1. Oil Pan

Oil Pan

The function of the oil pan is to store an adequate supply of oil for the lubrication system Figure 25. The deeper portion and larger volume of the pan connected to the oil pump pickup is called the sump . While more than enough oil is available in the oil pan to supply the lubrication requirements of the engine, excess oil is needed to distribute contaminant loading of lubrication oil and to provide a reserve capacity to compensate for oil consumption. Oil volumes pumped by the engine can easily recirculate all the oil sump capacity in under a minute. With increased oil pan capacity, longer intervals between drain periods can be set by the manufacturer. The location of the oil pan provides some cooling of engine oil, which is normally at temperatures above coolant operating temperature. Excess oil capacity allows the oil to remain in the pan longer and cooler. An oil pan may be made of fiberglass, stamped steel, or aluminum Figure 26. Significant engine noise originates from the oil pan, so it may be covered in sound-insulating material.

FIGURE 10-25: The plastic oil pan, or sump, holds in excess of 11 gallons (40 L) of oil. The plastic material helps dampen engine noise.

FIGURE 10-26: The aluminum oil pan of this off-road diesel contains baffles to prevent the sloshing of oil. Aluminum helps reduce engine weight and improves heat transfer from oil.

As mentioned, the sump is the deepest part of the oil pan where the oil pump pickup tube is located. Depending on the chassis configuration, the sump may be located at the rear, front, or middle of the engine to accommodate suspension-of-frame component clearances. Two drain plugs may be used in the sump and at the other end of the oil pan to ensure that as much contaminated oil is drained as possible.

An oil dipstick measures the level of engine oil when the engine is off Figure 27. A windage tray may also be incorporated into the oil pan or just above the pan. Windage trays separate the crankcase from the oil pan reservoir to prevent the crankshaft from whipping engine oil stored in the pan Figure 28. The primary advantage of the tray is that it can increase fuel economy by as much as 1–2%. The tray also prevents customer complaints in LD and MD engines, such as engine thumping and stumbling during cornering or braking, when oil can surge up into the crankcase area. Additionally, the oil-level sensor used in the lower pan warns the driver if oil levels are dangerously low.

FIGURE 10-27: The engine oil dipstick measures the level of oil when the engine is off. The oil level should be between the hash marks. Overfilling will cause seals to leak and aerate the oil.

FIGURE 10-28: The windage tray from a Mack MP7 engine. A windage tray prevents oil from interfering with crankshaft motion and causing oil foam.

1.2. Oil Pump

Oil Pump

The oil pump is used to pressurize the lubrication system of a diesel engine. It is a positive displacement pump, usually constructed with a closed-gear or gerotor design. A gerotor pump is constructed of an inner rotor and an outer rotor. The inner rotor turns inside the outer rotor ring, which also turns. The inner rotor has one less lobe than the outer ring and is positioned off-center from the outer ring. As the lobes slide up and over one another, oil is drawn through a fixed passageway connected to the oil pump pickup tube. Oil is squeezed out into the main oil gallery through the outlet passageway behind the rotors Figure 29. The external gear pump is another common configuration for an engine oil pump. This pump has two opposing gears. A drive shaft turns one gear, which in turn rotates the opposite gear. Oil is trapped and carried around the pump between the gear teeth. A seal is formed between the gear teeth and the oil pump housing Figure 30.

FIGURE 10-29: A gerotor oil pump.

FIGURE 10-30: An internal gear oil pump.

FIGURE 10-31: Oil is drawn into the pickup tube through a screen. The pickup tube is located in the sump of the oil pan.

The lube oil is supplied under pressure to moving parts through drilled passageways in the engine called oil galleries . Most moving parts are supplied pressurized oil for lubrication; however, cylinder walls are lubricated by oil thrown off engine bearings and from oil cooler nozzles. Oil is drawn into the pump through a pickup tube and screen located in the oil pan sump Figure 31. When replacing oil pumps, they should be primed to shorten the time required to develop engine oil pressure. The pickup tube inlet screen should be cleaned and inspected for blockages.

Variable Displacement Oil Pumps
The oil pump is a common target for achieving energy reductions in today’s diesels. Several engines now use flow rate-controlled oil pumps or two-stage pumps that operate at either a high-pressure or a low-pressure setting, depending on operating requirements Figure 32. Data from the oil pressure sensor and the engine ECU calculations are used to electrically switch the oil pump between the two pressure stages, depending on engine load, speed, and oil temperature. Power consumption by the oil pump is reduced when driving in low-speed urban or off-road conditions when high oil pump volume and pressure are not required. A common type of a flow rate-controlled vane pump regulates pump delivery volume by rotating an eccentric adjustable ring that surrounds the pump vanes. The space between the pump vanes is increased or decreased to change pump output volume. A hydraulic control valve rotates the ring against spring pressure to vary the space swept by the pump vanes Figure 33.

FIGURE 10-32: The oil pressure produced from a two-stage pump with an electronically controlled pressure-relief valve.

FIGURE 10-33: A flow rate-controlled pump. Components of a variable displacement oil pump that are used to save energy. The area of the delivery space above the pump vanes is mechanically varied to optimally match engine requirements for oil pressure.

1.3. Video: Oil Pumps

1.4. Anim: Oil Pump Types

1.5. Anim: Variable Displacement Oil Pump

1.6. Pressure-Regulating and Pressure-Relief Valve

Pressure-Regulating and Pressure-Relief Valve

Because the oil pump can pump more oil than the engine can use, an oil pressure-regulating valve is used to control oil pressure. Oil pressure that is too high can blow gaskets on the spin-on oil filter and burst or swell the oil filter into a pumpkin shape. Excessively high oil pressure can also erode engine bearings. Keeping the oil pressure regulated between 20–40 psi (138–276 kPa) when the engine oil is warm can reduce parasitic power loss caused by pumping more oil than is necessary TABLE 10-5.

The oil pressure-regulating valve is usually located in the main oil gallery or at the outlet of an oil pump Figure 34. Using a conventional spring-loaded bypass valve arrangement permits maximum oil pressure control by the valve. When oil pressure reaches a value equal to the spring tension of a pressure-regulating valve, spring pressure is overcome by oil pressure, which moves a spool valve to a bypass position. Oil returns to the sump in quantities proportional to the excess volume produced by the oil pump Figure 35. As long as clearances between engine bearings and other components using oil remain closed, adequate oil pressure is maintained by the oil pump and pressure-regulating valve. If an engine has excessive wear or internal oil leaks, oil pressure will drop as the pump tries to make up for the additional volume required by the leaks and larger operating clearances in the engine lubrication system.

FIGURE 10-34: The oil pressure relief valve of an HD diesel oil pump. Note that there are two points to attach the pump pickup tube. One can be used for either a front sump oil pan or a rear sump.

FIGURE 10-35: Operation of the oil pressure-regulating valve. When oil pressure exceeds a calibrated spring tension of the regulator, the check ball will uncover a passageway, permitting excess oil to return to the sump.

In the event that the pressure-regulating valve cannot relieve oil pressure fast enough, such as when the oil is cold and thick or when the regulator is not properly working, a pressure-relief valve is connected in series with the pressure regulator. This valve will typically open at 100 psi (689 kPa) and return oil to the sump Figure 36.

To electronically regulate oil pump pressure, an electronically controlled pressure-regulating valve can operate to spill or return excess oil back into the oil pump inlet. The pulse- width–modulated control valve will operate in a closed control loop with the oil pressure sensor and open to reduce oil pressure Figure 37.

FIGURE 10-36: A schematic view of typical oil circuits found in a diesel engine. This is a V8 engine.

FIGURE 10-37: An electronically controlled pressure regulator spills pressurized oil back into the oil pump inlet.

1.7. Anim: Engine Oil Pressure Control

1.8. Oil Cooler

Oil Cooler

An oil cooler is a heat exchanger used to remove excess heat from engine oil Figure 38. Virtually all diesel engines use oil coolers because more cooling of pistons and other internal engine parts is performed using lubrication oil. Engine oil can easily become overheated while absorbing heat from pistons, turbochargers, and other internal parts, particularly when the engine is heavily loaded. Oil cooling nozzles or drilled passageways in the connecting rods direct lubricating oil to the underside of the piston crown to prevent heat damage and ring seizure Figure 39. The result is higher heat loads transferred to the lubricating system in a diesel engine. Engine oil should never exceed 250° F (139° C). Many electronic engines use oil temperature sensors to shut down or derate engine power if oil temperatures exceed 250–260° F (139–143° C). When under load, normal engine oil temperature should not exceed the temperature of the coolant by more than 30–40° F (−1.1 to 4.4° C). This means an engine operating at 190–205° F (88–96° C) should have a maximum oil temperature of 220–245° F (122–136° C).

FIGURE 10-38: The lubrication system often uses oil modules incorporating filters, pressure control valves, and oil coolers into a single base.

FIGURE 10-39: The cooling nozzle is aimed at the underside of the piston crown. A notch in the piston prevents contact with the oil cooler nozzle.

Oil coolers are usually thermostatically controlled to prevent either oil or coolant to flow through the cooler until the oil or coolant has warmed up Figure 40. This feature prevents prolonged circulation of poorly lubricating, highly viscous cold oil during warm-up Figure 41. Ideally, oil should warm up quickly and before coolant reaches operating temperature to easily circulate into narrow operating clearances. When the oil or coolant reaches operating temperature, oil diverts into the cooler where it releases excess heat to the cooling system Figure 42. The cooler may also be equipped with a pressure-relief valve that allows oil to bypass the cooler if it becomes plugged with unfiltered oil contaminants. The bypass valve opens if a substantial pressure drop occurs across the cooler.

FIGURE 10-40: Oil circuits of a late-model Mack MP8 engine. Note the location of various control valves, the oil thermostat, the oil galleries, and the number of parts requiring lubrication.

FIGURE 10-41: Engine coolant circulates around the outside of this plate-type cooler.

FIGURE 10-42: Location of an oil temperature thermostat and oil pressure-regulating valve for the lubrication system in an oil cooler-lubrication system module.

Oil Cooler Failures
Engine coolant will usually remove heat from an oil cooler. Plate- and tube-type oil coolers are the most commonly used designs (Figure 43 and Figure 44). Defective coolers or poor maintenance of the cooling system can lead to cooler corrosion, which will cause oil to enter the engine coolant. Oil enters the cooling system because the oil pressure is higher than the pressure in the cooling system. Metal cooler tubes and plates can easily corrode if the pH of the cooling system becomes either too acidic or too alkaline, depending on the plate metal. A suspected leaking cooler can be removed from the engine and pressurized with air to confirm that it is leaking because other engine defects can also push oil into the cooling system. Cooling systems must be drained and flushed after a cooler is replaced if oil has contaminated the coolant.

FIGURE 10-43: A tube-type cooler and oil cooler bundle using internal tubes and plates.

FIGURE 10-44: An oil cooler used on an International diesel truck engine. Oil passes through the bundle tubes and coolant circulates around the cooler bundle.

Another problem with coolers is that they can become contaminated and plugged with crankcase debris. To ensure that high oil flow takes place through the cooler, manufacturers generally send unfiltered oil through a cooler before it enters the oil filters. In that situation, the cooler functions like a primary oil filter. Soot, oil sludge, and debris, such as pieces of gaskets, silicone sealant used as a gasket material, and dirt, can clog cooler passageways. For this reason, a cooler bypass valve is needed to prevent oil starvation if the cooler becomes plugged. Engine bearing failures will also fill the cooler with metal debris, which requires the cooler to be reverse flushed with solvent before the cooler is returned to service after an engine repair or overhaul. One symptom of a plugged cooler is a sudden drop in oil pressure during engine warm-up. Because coolers normally do not allow oil through the core until the oil or coolant is warmed up, oil pressure is normal until the cooler thermostat diverts oil to pass through the cooler. If the cooler is clogged, oil pressure suddenly drops after engine warm-up.

Technicians Tip     Oil coolers are often installed in series with other components dependent on coolant or oil flow Figure 45. Restricted coolant flow due to a partially blocked oil cooler can cause problems for those downstream devices. Unless a technician is vigilant in understanding how the coolant or oil flow circuits are arranged in an engine, failures in downstream components are often difficult to diagnose or have repeat failures after replacement. One common example is EGR cooler failures. Coolant flow through a coolant-restricted oil cooler also restricts coolant flow to an EGR cooler if it is connected in series. In that situation, coolant will boil in the EGR cooler and thermally stress it, quickly causing a failure in the EGR cooler.

FIGURE 10-45: The oil cooler of this Detroit Series 60 engine is located above the oil filters. Note the coolant pipe attached directly to the water pump outlet.

1.9. Video: Oil Coolers

1.10. Oil Filter

Oil Filter

The purpose of lubrication-oil filtration is contamination removal. Oil contamination can allow abrasives to rapidly wear engine components if not properly controlled. Soot, sludge, and dirt are the most common contaminants removed by the filtration system. The choice of filter capacity and type of filter media are determined by the degree of cleanliness desired for the lubrication oil.

Filter Media
The type of filter media used inside the oil filter depends on a number of variables, including particle-removal efficiency, contaminant holding capacity, resistance to flow, and the corresponding pressure drop of a full filter. There are between 50–75 different media grades designed for oil filtration that are available to filter manufacturers Figure 46. Media used for air, coolant, and oil filtration cannot be used interchangeably. Types of oil filter media range from mesh-like screens to thread or chopped paper to 100% natural cellulose and 100% synthetic microfibers.

A	B		FIGURE 10-47: Cutaway of a bypass filter that uses cellulose-microglass filter media. Unfiltered oil enters the case on the outside of the filter and must pass through the filter media to the filter center. The bypass filter has two different types of media supplied with one inlet but two separate outlets.
FIGURE 10-46: Two oil filters. A. Paper filter with yellow media. B. Microglass filter with white media.

When only large particles are to be removed, a cellulose or paper media is used. To remove progressively smaller particles, the type of media changes from complex cellulose to blended media containing cellulose and microfiber materials. Cellulose or paper typically provide filtration of particles larger than 13–20 microns. Glass microfiber, or microglass, provides the most efficient filtration with the least amount of restriction, but it is usually the most expensive to manufacture. Microglass filtration is capable of removing particles as small as 2–5 microns Figure 47. Pleated filters provide more surface area for holding contaminants; however, too many pleats can swell and prevent oil flow.

Because diesel engine oil contains a substantial amount of soot, more than one filter is used, and bypass filters are commonly used in addition to the full-flow filters that supply oil directly to engine bearings Figure 48. Bypass filters supplement regular filtration by filtering oil and returning it to the oil pan. Paper depth filters and spinner or centrifugal bypass filters are commonly used. Centrifugal bypass filters often use a replaceable paper filter that separates soot by spinning a filter core at high speeds, using oil pressure to drive the spinner core Figure 49. The thin paper, which is replaceable in many bypass spinners, traps and separates soot from oil.

FIGURE 10-48: This engine uses two full-flow filters and one bypass filter.

FIGURE 10-48: A centrifugal bypass filter removes soot using a high-speed centrifuge driven by engine oil pressure.

1.11. Anti-Drainback Valve

Anti-Drainback Valve

Cartridge filters and spin-on oil filters, which are filter elements consisting simply of filter media enclosed by metal containers, require an anti-drainback valve. Spin-on filters usually have this valve built into the filter element, but the filter header—the component that the filter threads onto—contains the valve. The purpose of the drainback valve is to prevent the oil in the engine from returning to the crankcase when the engine is shut down. This permits the instantaneous buildup of oil pressure and immediate supply of oil to the engine after start-up. This valve usually consists of a one-way flow control valve in the center tube of a spin-on filter. Many drainback valves in filters are made of nitrile rubber. However, nitrile rubber diaphragms stiffen in extreme cold and may fail to seal in those conditions. Silicone rubber seals or steel valves are not prone to this problem. Detroit Diesel (DD)-series engines and other OEMs use a check valve in the oil pump pickup tube to prevent oil from draining back to the pan when the engine is shut down.

1.12. Oil Filter Bypass Valves

Oil Filter Bypass Valves

The bypass valve features pressure control valves and is incorporated into the filter, filter housing, or lubrication system module. The bypass valve allows oil to pass from the dirty side to the clean side of the filter if resistance or restriction is excessive across the filter media Figure 50. This prevents oil starvation of the engine in the event of a plugged filter. The simplest bypass valve design uses a spring-loaded filter element that causes the spring located beneath the element to compress if the oil pressure differential across the filter element becomes too high Figure 51. Compressing the spring moves the filter away from the base, allowing a direct connection between the filter inlet and the outlet. This condition permits oil to move directly from the dirty filter inlet through to the filtered center of the element without passing through the filter media.

FIGURE 10-50: Types of filter bypass mechanisms. Most HD diesels incorporate an additional bypass valve in the filter header.

FIGURE 10-51: A bypass valve located in the header of the oil filter. The bypass valve opens when filter restriction is too high, and dirty oil is then circulated through the engine.

To supplement the filter bypass valve, an oil filter bypass relief valve is often found in the oil filter header of many engines. Its purpose is identical to the filter bypass valve in a cartridge filter: it allows pressurized oil to bypass a plugged filter. The filter bypass valve operates on principles of pressure differential. Usually, when a new oil filter is installed, very little pressure drop occurs across the filter media. With increasing contamination, however, the filter becomes restrictive and a progressively larger pressure drop occurs across the filter. Typically, when the pressure drop exceeds approximately 3–30 psi (21–207 kPa), the bypass valve opens and allows unfiltered oil to flow into the main oil gallery. Without the bypass valve, the pressure differential across the filter media would burst or internally tear the filter.

1.13. Anim: Engine Oil Filter