5.2 Engine Lubricating Systems

All internal combustion engines are equipped with an internal lubricating system (Figure 5-14). Without lubrication, an engine quickly overheats and its working parts seize due to excessive friction. All moving parts must be adequately lubricated to assure maximum wear and long engine life.

Figure 5-14 — Engine lubrication system.

Purposes of Lubrication

The functions of an engine lubrication system are as follows:

• Reduces friction and wear between moving parts (Figure 5-15).

Figure 5-15 — How oil lubricates.

• Helps transfer heat and cool engine parts.

• Cleans the inside of the engine by removing contaminants (metal, dirt, plastic, rubber, and other particles).

• Absorbs shocks between moving parts to quiet engine operation and increase engine life.

The properties of engine oil and the design of modern engines allow the lubrication system to accomplish these functions.

Engine Oil

Engine oil, also called motor oil, is used to produce a lubricating film on the moving parts in an engine. The specification for this type of oil prescribes that the oil should be petroleum or a synthetic petroleum product, or a combination thereof.

This oil is intended for lubrication of internal-combustion engines other than aircraft engines or for general-purpose lubrication.

Oil Viscosity and Measurements

Oil viscosity, also called oil weight, is the thickness or fluidity (flow ability) of the oil. High viscosity oil is very thick and resists flow. A low viscosity oil is very thin and flows easily.

Oils are graded according to their viscosity by a series of Society of Automotive Engineers (SAE) numbers. The viscosity of the oil increases progressively with the SAE number. An SAE 4 oil would be very light (low viscosity) and SAE 90 oil would be very heavy (high viscosity). The viscosity of the oil used in internal-combustion engines ranges from SAE 5 (arctic use) to SAE 60 (desert use). It should be noted that the SAE number of the oil has nothing to do with the quality of the oil.

The viscosity number of the oil is determined by heating the oil to a predetermined temperature and allowing it to flow through a precisely sized orifice while measuring the rate of flow. The faster an oil flows, the lower the viscosity. The testing device is called a viscosimeter. The viscosity of the oil is printed on top of the oil can. Oil viscosity is written SAE 10, SAE 20, SAE 30, and so on. The letter W will follow any oil that meets SAE low-temperature requirements. An example would be SAE 10W.

Multi-viscosity oil or multi-weight oil has the operating characteristics of a thin, light oil when cold and a thicker, heavy oil when hot. A multi-weight oil is numbered SAE 10W- 30, 10W-40, 20W-50, and so on. For example, a 10W-30 oil will flow easily (like 10W oil) when starting a cold engine. It will then act as a thicker oil (like 30 weight) when the engine warms to operating temperature. This will make the engine start more easily in cold weather. It will also provide adequate film strength (thickness) when the engine is at full operating temperature.

Normally, you should use the oil viscosity recommended by the manufacturer. However, in a very cold, high mileage, worn engine, higher viscosity may be beneficial. Thicker oil will tend to seal the rings and provide better bearing protection. It may also help cut engine oil consumption and smoking.

Oil Service Rating

The oil service rating is a set of letters printed on the oil can to denote how well the oil will perform under operating conditions. The American Petroleum Institute (API) sets this performance standard.

The API system for rating oil classifies oil according to its performance characteristics. The higher rated oils contain additives that provide maximum protection against rust, wear, oil oxidation, and thickening at high temperatures. Oils designed for gasoline engines fall under the “S” categories as shown in Table 5-1.

Table 5-1 — System rating of oils designed for gasoline engines.

Category Status Service
SA Obsolete Adequate for utility engines subjected to light loads, moderate speeds, and clean conditions. Straight mineral oil. Contains no additives. For older engines, use only when specifically recommended by the manufacturer.


Obsolete Adequate for automotive use under favorable conditions (light loads, low speeds, and moderate temperatures) with relatively short oil change intervals. Generally offers only minimal protection to the engine against bearing scuffing, corrosion, and oil oxidation. Use only when specifically recommended by the manufacturer.
SC Obsolete For 1964 through 1967 automotive gasoline engines.
SD Obsolete For 1968 through 1970 automotive gasoline engines. Offers additional protection over SC oils that are necessary with the introduction of emission controls.
SE Obsolete For 1972 through 1979 automotive gasoline engines. Stricter emission requirements created the need for this detergent oil.
SF Obsolete For 1980 through 1988 automotive gasoline engines. The SF oil is designed to meet the demands of small, high-revving engines.
SG Obsolete For 1989 through 1993 automotive gasoline engines.
SH Obsolete For 1994 through 1996 automotive gasoline engines.
SJ Current For 1997 through 2001 automotive gasoline engines.
SL Current For 2001 through 2003 automotive gasoline engines.
SM Current For 2004 through present automotive gasoline engines. Designed to provide a superior resistance to oxidation and provide better engine wear.

Oils designed for diesel engines fall under the “C” category as shown in Table 5-2.

Table 5-2 — System rating of oils designed for diesel engines.

Category Status Service
CA Obsolete For naturally aspirated diesel engines operated on low sulfur fuel, mainly used in the 1940s and 1950s.
CB Obsolete For naturally aspirated diesel engines operated on high sulfur fuel used in the 1950s.
    CC Obsolete For lightly supercharged diesel engines, introduced in 1961.

CD Obsolete For moderately supercharged diesel engines, introduced in 1955.

CD-II Obsolete For two-stroke cycle diesel engines. Meets requirements of API Service category CD.
CE Obsolete For moderately supercharged diesel engines, introduced in 1983. Typical for high load and high speed, also meets requirements of API Service category CD.
CF Current For indirect-injection diesel engines that use a broad range of diesel fuel, may be used when category CD is recommended.
CF-2 Current For severe duty two-stroke cycle diesel engines, may be used when category CD-II is recommended.
CF-4 Obsolete For high-speed four-stroke cycle naturally aspirated and turbocharged diesel engines, may be used when category CD and CE are recommended.
CG-4 Obsolete For severe duty, high-speed four-stroke cycle with less than 0.5% weight sulfur, may be used when category CD, CE and CF-4 are recommended.
CH-4 Current For high-speed four-stroke cycle with less than 0.5% weight sulfur to meet 1988 emissions, may be used when category CD, CE, CF-4 and CG-4 are recommended.
CI-4 Current For high-speed four-stroke cycle with less than 0.5% weight sulfur to meet 2004 emissions where EGR is used, may be used when category CD, CE, CF-4, CG-4 and CH-4 are recommended. Some CI-4 oils qualify for the PLUS designation by providing a higher level protection soot-related viscosity break down.
CJ-4 Current For high-speed four-stroke cycle with less than 0.05% weight sulfur to meet 2007, may be used when category CD, CE, CF-4, CG-4 and CH-4 are recommended. CJ-4 oils exceed the performance criteria of CI-4, CI-4 PLUS, CF-4, CH-4, and CG-4.

The operator's manual provides the service rating recommended for a specific vehicle. You can use a better service rating than recommended, but NEVER a lower service rating. A high service rating (SM, for example) can withstand higher temperatures and loads while still maintaining a lubricating film. It will have more oil additives to prevent oil oxidation, engine deposits, breakdown, foaming, and other problems.

Lubricating (Oil) System Components

You must remember that the lubricating system is actually an integral part of the engine and the operation of one depends upon the operation of the other. Thus the lubricating system, in actual practice, cannot be considered as a separate and independent system; it is part of the engine. The lubricating system basically consists of the following:

• Oil pump—forces oil throughout the system.

• Oil pickup and strainers—carries oil to the pump and removes large particles.

• Pressure relief valve—limits maximum oil pressure.

• Oil filter—strains out impurities in the oil.

• Oil cooler—provides cooling for the oil system.

• Oil pan—reservoir or storage area for engine oil.

• Oil level gauge—checks the amount of oil in the oil pan.

• Oil galleries—oil passages through the engine.

• Oil pressure indicator—warns the operator of low oil pressure.

• Oil pressure gauge—registers actual oil pressure in the engine.

• Oil temperature regulator—controls engine oil temperature on diesel engines.

Oil Pump

The oil pump is the heart of the lubricating system; it forces oil out of the oil pan, through the oil filter and galleries, and to the engine bearings. Normally, a gear on the engine camshaft drives the oil pump; however, a cogged belt or a direct connection with the end of the camshaft or crankshaft drives the pump in some cases.

There are two basic types of oil pumps— rotary and gear.

The rotary pump has an inner rotor with lobes that match similar shaped depressions in the outer rotor (Figure 5-16). The inner rotor is off center from the outer rotor.As the oil pump shaft turns, the inner rotor causes the outer rotor to spin. The eccentric action of the two rotors forms pockets that change size. A large pocket is formed on the inlet side of the pump. As the rotors turn, the oil-filled pocket becomes smaller as it nears the outlet of the pump. This action squeezes the oil and makes it spurt out under pressure. As the pump spins, this action is repeated over and over to produce a relatively smooth flow of oil.

Figure 5-16 — Rotary oil pump.

The gear pump consists of two pump gears mounted within a close-fitting housing (Figure 5-17). A shaft, usually turned by the distributor, crankshaft, or accessory shaft, rotates one of the pump gears. The gear turns the other pump gear that is supported on a short shaft inside the pump housing.

Figure 5-17 — Rotary oil pump.

Oil on the inlet side of the pump is caught in the gear teeth and carried around the outer wall inside the pump housing. When oil reaches the outlet side of the pump, the gear teeth mesh and seal. Oil caught in each gear tooth is forced into the pocket at the pump outlet and pressure is formed. Oil squirts out of the pump and to the engine bearings.

As a safety factor to assure sufficient oil delivery under extreme operating conditions, the oil pump (gear or rotary) is designed to supply a greater amount of oil than is normally required for adequate lubrication. This requires that an oil pressure relief valve be incorporated in the pump to limit maximum oil pressure.

Oil Pickup and Strainer

The oil pickup is a tube that extends from the oil pump to the bottom of the oil pan. One end of the pickup tube bolts or screws into the oil pump or to the engine block. The other end holds the strainer.

The strainer has a mesh screen suitable for straining large particles from the oil and yet passes a sufficient quantity of oil to the inlet side of the oil pump. The strainer is located so all oil entering the pump from the oil pan must flow through it. Some assemblies also incorporate a safety valve that opens in the event the strainers become clogged, thus bypassing oil to the pump. Strainer assemblies may be either the floating or the fixed type.

The floating strainer has a sealed air chamber, is hinged to the oil pump inlet, and floats just below the top of the oil. As the oil level changes, the floating intake will rise or fall accordingly. This action allows all oil taken into the pump to come from the surface. This design prevents the pump from drawing oil from the bottom of the oil pan where dirt, water, and sludge are likely to collect. The strainer screen is held to the float by a holding clip. The up-and-down movement of the float is limited by stops.

The fixed strainer is simply an inverted funnel-like device placed about 1/2 inch to 1 inch from the bottom of the oil pan (Figure 5-18). This device prevents any sludge or dirt that has accumulated from entering and circulating through the system. The assembly is attached solidly to the oil pump in a fixed position.

Figure 5-18 — Oil pick up and strainer.

Pressure Relief Valve

The pressure relief valve is a spring-loaded bypass valve in the oil pump, engine block, or oil filter housing. The valve consists of a small piston, spring, and cylinder. Under normal pressure conditions, the spring holds the relief valve closed. All the oil from the oil pump flows into the oil galleries and to the bearings.

However, under abnormally high oil pressure conditions (cold, thick oil, for example), the pressure relief valve opens. Oil pressure pushes the small piston back in its cylinder by overcoming spring tension. This allows some oil to bypass the main oil galleries and pour back into the oil pan. Most of the oil still flows to the bearings and a preset pressure is maintained. Some pressure relief valves are adjustable. By turning a bolt or screw or by changing spring shim thickness, you can alter the pressure setting.

Oil Filter

The oil filter removes most of the impurities that have been picked up by the oil as it circulates through the engine. Designed to be replaced readily, the filter is mounted in an accessible location outside the engine. There are two basic filter element configurations—the cartridge type and spin-on type.

The cartridge-type element fits into a permanent metal container (Figure 5-19). Oil is pumped under pressure into the container where it passes from the outside of the filter element to the center. From here, the oil exits the container. The element is changed easily by removing the cover from the container.

The spin-on filter is completely self-contained, consisting of an integral metal container and filter element (Figure 5-19). Oil is pumped into the container on the outside of the filter element. The oil then passes through the filter medium to the center of the element where it exits the container. This type of filter is screwed onto its base and is removed by spinning it off.

Figure 5-19 — Oil filters.

The elements themselves may be either metallic or nonmetallic. Cotton waste and resin-treated paper are the most popular filter mediums. They are held in place by sandwiching them between two perforated metal sheets. Some heavy-duty applications use layers of metal that are thinly spaced apart. Foreign matter is strained out as the oil passes between the metal layers.

There are two filter configurations: the full-flow system and the bypass system. The operations of both systems are as follows:

• The full-flow system is the most common (Figure 5-20). All oil in a full-flow system is circulated through the filter before it reaches the engine. When a full-flow system is used, it is necessary to incorporate a bypass valve in the oil filter to allow the oil to circulate through the system without passing through the element in the event that it becomes clogged. This prevents the oil supply to the engine from being cut off.

• The bypass system diverts only a small quantity of oil each time it is circulated and returns it directly to the oil pan after it is filtered. This type of system does not filter the oil before it is sent to the engine. The oil from the main oil gallery enters the filter and flows through the filter element. It then passes into the collector in the center of the filter. The filtered oil then flows out a restricted outlet, preventing the loss of pressure. The oil then returns directly to the oil pan.

Figure 5-20 — Full flow oil system.

Oil Cooler

Some engines require an additional oil cooler (Figure 5-21) to help lower and control the operating temperature of the engine oil. It consists of a radiator-like device, called a heat exchanger, connected to the lubrication system by the use of an oil cooler adapter. Oil is pumped through the cooler before it flows back into the engine.

Figure 5-21 — Oil cooler.

The heat exchanger looks like a small radiator that is fitted onto the vehicle in front of the radiator. Air flows across the fins of the heat exchanger, cooling the oil before it goes back into the engine.

The oil cooler adapter is a device that fits between the filter and the oil filter housing. It provides hose connections for the oil lines leading to and from the heat exchanger.

Oil Pan

The oil pan is normally made of thin sheet metal or aluminum, and bolts to the bottom of the engine block. It holds a supply of oil for the lubrication system. The oil pan is fitted with a screw-in drain plug for oil changes. Baffles may be used to keep the oil from splashing around in the pan.

The sump is the lowest area in the oil pan where oil collects. As oil drains from the engine, it fills the sump. Then the oil pump can pull oil out of the pan for recirculation.

Oil Level Gauge

The oil level gauge, also known as a dipstick, is usually of the bayonet type (Figure 5-22). It consists of a long rod or blade that extends into the oil pan. It is marked to show the level of oil within the oil pan. Readings are taken by pulling the rod out from its normal place in the crankcase, wiping it clean, replacing it, and again removing and noting the height of the oil on the lower or marked end. This should be done with the engine stopped unless the manufacturer recommends otherwise. It is important that the oil level not drop below the low mark or rise above the full mark.

Figure 5-22— Dipstick.

Oil Galleries

Oil galleries are small passages through the cylinder block and head for lubricating oil. They are cast or machined passages that allow oil to flow to the engine bearings and other moving parts.

The main oil galleries are large passages through the center of the block. They feed oil to the crankshaft bearings, camshaft bearings, and lifters. The main oil galleries also feed oil to smaller passages running up to the cylinder heads.

Oil Pressure Warning Light

The oil pressure warning light is used in place of a gauge on many vehicles. The warning light, although not as accurate, is valuable because of its high visibility in the event of a low oil pressure condition. Because the engine can fail or be damaged in less than a minute of operation without oil pressure, the warning light is used as a backup for a gauge to attract instant attention to a malfunction.

The warning light receives battery power through the ignition switch. The circuit to ground is completed through the oil pressure-sending unit that screws into the engine and is exposed to one of the oil galleries. The sending unit consists of a pressure- sensitive diaphragm that operates a set of contact points. The contact points are calibrated to turn on the warning light anytime oil pressure drops below approximately 15 psi in most vehicles.

Oil Pressure Gauge

The oil pressure gauge is mounted on the instrument panel of a vehicle. Marked off on a dial in pounds per square inch (psi), the gauge indicates how regularly and evenly the oil is being delivered to all vital parts of the engine and warns of any stoppages in this delivery. Pressure gauges may be electrical or mechanical.

In the mechanical type, the gauge on the instrument panel is connected to an oil line tapped into an oil gallery leading from the pump. The pressure of the oil in the system acts on a diaphragm within the gauge, causing the needle to register on the dial.

In the electrical type, oil pressure operates a rheostat connected to the engine that signals electrically to the pressure gauge indicating oil pressure within the system.

Oil Temperature Regulator

The oil temperature regulator must be used in diesel engine lubricating systems. It prevents oil temperature from rising too high in hot weather, and assists in raising the temperature during cold starts in winter weather. It provides a more positive means of controlling oil temperature than does cooling by radiation of heat from the oil pan wells.

The regulator uses engine coolant in the cooling system to regulate the temperature of the oil and is made up of a core and housing. The core, through which the oil circulates, is of cellular or bellows construction and is built to expose as much oil as possible to the coolant that circulates through the housing. The regulator is attached to the engine so that the oil will flow through the regulator after passing through the pump. As the oil passes through the regulator, it is either cooled or heated, depending on the temperature of the coolant, and then is circulated through the engine.

Types of Lubricating (Oil) Systems

Now that you are familiar with the lubricating system components, you are ready to study the different systems that circulate oil through the engine. The systems used to circulate oil are known as splash, combination splash force feed, force feed, full force feed, and dry sump.


The splash system is no longer used in automotive engines. It is widely used in small four-cycle engines for lawn mowers, outboard marine operation, and so on.

In the splash lubricating system, oil is splashed up from the oil pan or oil trays in the lower part of the crankcase (Figure 5-23). The oil is thrown upward as droplets or fine mist and provides adequate lubrication to valve mechanisms, piston pins, cylinder walls, and piston rings.

Figure 5-23— Splash type oil system.

In the engine, dippers on the connecting- rod bearing caps enter the oil pan with each crankshaft revolution to produce the oil splash. A passage is drilled in each connecting rod from the dipper to the bearing to ensure lubrication.

This system is too uncertain for automotive applications. One reason is that the level of oil in the crankcase will greatly vary the amount of lubrication received by the engine. A high level results in excess lubrication and oil consumption, and a slightly low level results in inadequate lubrication and failure of the engine.

Force Fed

A somewhat more complete pressurization of lubrication is achieved in the force feed lubrication system (Figure 5-24). Oil is forced by the oil pump from the crankcase to the main bearings and the camshaft bearings. Unlike the combination system, the connecting-rod bearings are also fed oil under pressure from the pump.

Figure 5-24 — Force fed oil system.

Oil passages are drilled in the crankshaft to lead oil to the connecting-rod bearings. The passages deliver oil from the main bearing journals to the rod bearing journals. In some engines, these opening are holes that line up once for every crankshaft revolution. In other engines, there are annular grooves in the main bearings through which oil can feed constantly into the hole in the crankshaft.

The pressurized oil that lubricates the connecting rod bearings goes on to lubricate the pistons and walls by squirting out through strategically drilled holes. This lubrication system is used in virtually all engines that are equipped with semi-floating piston pins.

Combination Splash and Force Fed

In a combination splash and force feed, oil is delivered to some parts by means of splashing and to other parts through oil passages under pressure from the oil pump (Figure 5-25).

Figure 5-25 — Combination splash and force fed oil system.

The oil from the pump enters the oil galleries. From the oil galleries, it flows to the main bearings and camshaft bearings. The main bearings have oil-feed holes or grooves that feed oil into drilled passages in the crankshaft. The oil flows through these passages to the connecting rod bearings. From there, on some engines, it flows through holes drilled in the connecting rods to the piston-pin bearings.

Cylinder walls are lubricated by splashing oil thrown off from the connecting-rod bearings. Some engines use small troughs under each connecting rod that are kept full by small nozzles which deliver oil under pressure from the oil pump. These oil nozzles deliver an increasingly heavy stream as speed increases. At very high speeds these oil streams are powerful enough to strike the dippers directly. This causes a much heavier splash so that adequate lubrication of the pistons and the connecting-rod bearings is provided at higher speeds.

If a combination system is used on an overhead valve engine, the upper valve train is lubricated by pressure from the pump.

Full Force Fed

In a full force feed lubrication system, the main bearings, rod bearings, camshaft bearings, and the complete valve mechanism are lubricated by oil under pressure. In addition, the full force feed lubrication system provides lubrication under pressure to the pistons and the piston pins. This is accomplished by holes drilled the length of the connecting rod, creating an oil passage from the connecting rod bearing to the piston pin bearing. This passage not only feeds the piston pin bearings but also provides lubrication for the pistons and cylinder walls. This system is used in virtually all engines that are equipped with full-floating piston pins.

Dry Sump

The dry sump lubrication system uses two oil pumps and a separate oil reservoir. No oil is stored in the oil pan itself. The main pump pulls oil from the reservoir and pushes it into the engine bearings and other high-friction points. The second pump, called the scavenge pump, pulls oil out of the pan and sends it to the oil reservoir.

These types of systems are found on exotic high-performance cars. Because there is no oil in the oil pan, engine horsepower and dependability are increased.

Lubricating System Problem Diagnosis

To troubleshoot an engine lubricating system, begin by gathering information on the problem. Ask the operator questions. Analyze the symptoms using your understanding of system operation. You should arrive at a logical deduction about the cause of the problem.

The four problems that most often occur in the lubrication system are as follows:

• High oil consumption (oil must be added frequently)

• Low oil pressure (gauge reads low, indicator light glows, or there are abnormal engine noises)

• High oil pressure (gauge reads high, oil filter swells)

• Indicator or gauge problems (inaccurate operation or readings)

When diagnosing these troubles, make a visual inspection of the engine for obvious problems. Check for oil leakage, a disconnected sending unit wire, low oil level, damaged oil pan, or other troubles that relate to the symptoms.

High Oil Consumption

If the operator must add oil frequently to the engine, this is a symptom of high oil consumption. External oil leakage out of the engine or internal leakage of oil into the combustion chambers causes high oil consumption. A description of each of these problems is as follows:

• External oil leakage—detected as darkened oil wet areas on or around the engine. Oil may also be found in small puddles under the vehicle. Leaking gaskets or seals are usually the source of external engine oil leakage.

• Internal oil leakage—shows up as blue smoke exiting the exhaust system of the vehicle. For example, if the engine piston rings and cylinders are badly worn, oil can enter the combustion chambers and will be burned during combustion.



Do not confuse black smoke (excess fuel in the cylinder) and white smoke (water leakage into the engine cylinder) with blue smoke caused by engine oil.

Low Oil Pressure

Low oil pressure is indicated when the oil indicator light glows, the oil gauge reads low, or the engine lifters or bearings rattle. The most common causes of low oil pressure are as follows:

• Low oil level (oil not high enough in pan to cover oil pickup)

• Worn connecting rod or main bearings (pump cannot provide enough oil volume)

• Thin or diluted oil (low viscosity or fuel in the oil)

• Weak or broken pressure relief valve spring (valve opens too easily)

• Cracked or loose pump pickup tube (air is being pulled into the oil pump)

• Worn oil pump (excess clearance between rotors or gears and housing)

• Clogged oil pickup screen (reduced amount of oil entering pump)

A low oil level is a common cause of low oil pressure. Always check the oil level first when troubleshooting a low oil pressure problem.

High Oil Pressure

High oil pressure is seldom a problem. When it occurs, the oil pressure gauge will read high. The most frequent causes of high oil pressure are as follows:

• Pressure relief valve stuck open (not opening at specified pressure)

• High relief valve spring tension (strong spring or spring has been improperly shimmed)

• High oil viscosity (excessively thick oil or use of oil additive that increases viscosity)

• Restricted oil gallery (defective block casting or debris in oil passage)

Indicator or Gauge Problems

A bad oil pressure indicator or gauge may scare the operator into believing there are major problems. The indicator light may stay on or flicker, pointing to a low oil pressure problem. The gauge may read low or high, also indicating a lubrication system problem.

Inspect the indicator or gauge circuit for problems. The wire going to the sending unit may have fallen off. The sending unit wire may also be shorted to ground (light stays on or gauge always reads high).

To check the action of the indicator or gauge, remove the wire from the sending unit. Touch it on a metal part of the engine. This should make the indicator light glow or the oil pressure gauge read maximum. If it does, the sending unit may be defective. If it does not, then the circuit, indicator, or gauge may be faulty.



Always check the service manual before testing an indicator or gauge circuit. Some manufacturers recommend a special gauge tester. This is especially important with some computer-controlled systems.

Lubricating System Maintenance

There are certain lubricating system service jobs that are more or less done automatically when an engine is repaired. For example, the oil pan is removed and cleaned during such engine overhaul jobs as replacing bearing or rings. When the crankshaft is removed, it is usual procedure to clean out the oil passages in the crankshaft. Also, the oil passages in the cylinder block should be cleaned out as part of the overhaul.

As a Construction Mechanic, you will be required to maintain the lubrication system. This maintenance normally consists of changing the oil and filter(s). Occasionally you will be required to perform such maintenance tasks as replacing lines and fittings, servicing or replacing the oil pump and relief valve, and flushing the system. The following discussion provides information that will aid you in carrying out these duties.

Oil and Filter Change

It is extremely important that the oil and filter(s) (Figure 5-26) of the engine are serviced regularly. Lack of oil and filter maintenance will greatly shorten engine service life.

Figure 5-26 — Oil and filter change.

Manufacturers give a maximum number of miles or hours a vehicle can be operated between oil changes. Newer automotive vehicles can be operated 5,000 miles between changes. Older automotive vehicles should have their oil changed about every 3,000 miles. Most construction equipment averages between 200 and 250 hours of operation between oil changes. However, depending on the climate and working conditions, the miles and hours between oil changes can be greatly reduced. Refer to the service manual for exact intervals.

To change the engine oil, warm the engine to full operating temperature, this will help suspend debris in the oil and make the oil drain more thoroughly. Unscrew the drain plug and allow the oil to flow into a catchment pan. Be careful of hot oil; it can cause painful burns.

Usually the filter elements are replaced at the same time the oil is changed. The most common filters are the spin-on filter or replaceable element type oil filter.

• Spin-on, throwaway oil filters—replaced as a complete unit. Unscrew the filter from the base by hand or a filter wrench and throw the filter away. When replacing, wipe the base clean with a cloth and place a small amount of oil or grease on the gasket to ensure a good seal. Screw on a new filter, tightening at least a half a turn after the gasket contacts the base. Do not use a filter wrench because the filter canister could distort and leak.

• Replaceable element oil filter—removed from the filter housing and replaced. Place a pan underneath the filter to catch oil from the filter. Remove the fastening bolt and lift off the cover or filter housing. Remove the gasket from the cover or housing and throw it away. Take out the old element and throw it away. Clean the inside of the filter housing and cover it. Install a new element and insert a new cover or housing gasket (ensure the gasket is completely seated in the recess). Replace the cover or housing and fasten it to the center bolt securely.

After the oil has been completely drained and the drain plug replaced, fill the crankcase to the full mark on the dipstick with the proper grade and weight of oil. Start and idle the engine. Check the oil pressure immediately. Inspect the filter or filter housing for leaks. Stop the engine and check the crankcase oil level and add to the full mark.


This chapter not only described engine cooling and lubricating systems, it also explained the harsh effects that can occur if they are not routinely cared for. By simply inspecting and replenishing coolant and oil levels, and inspecting a radiator, an operator can prevent major engine problems and extend the life of a piece of equipment.