LO 10-9 Identify potential causes of high oil consumption, the purpose and function of oil level sensors, and maintenance procedures to correct oil consumption

1. High Oil Consumption

High Oil Consumption

Engines can experience high oil consumption for a multitude of reasons, but ultimately oil is either being burned in the combustion chamber or leaking from the engine. When engine oil is leaking, the common procedure to identify an external leak location is to steam clean or power wash the engine. Then ultraviolet (UV) dye is added to the engine oil, and the engine is run at operating temperature for at least 20 minutes. A black light is then used to pinpoint the source of the leak. Gaskets, rear main seals, and turbochargers are common external leak paths for engine oil. Air compressors are frequently known to pump oil into the engine’s intake when unloaded, which produces unexplained high oil consumption. The air intake pipe to the compressor should be checked as well as the air reservoirs and air dryer for passing excessive amounts of oil.

Worn rings and valve guides are another point where oil can disappear into the engine. Worn rings allow oil into the combustion chamber. Piston rings that are coated in carbon, stuck, or seized can provide little to no oil control as well. These conditions are accompanied by excessive crankcase blowby, and if a road draft tube ventilates the crankcase, the area below and in the tube airstream will show heavy oil contamination. High crankcase pressure can also push more oil from a closed crankcase ventilation system into a turbocharger or engine intake system. Thin oil or oil that does not have the correct viscosity will more easily pass between tight clearances between valve guides, the piston, and the cylinder walls.

Related to high oil consumption is a high oil level. In this situation, the engine appears to “make” oil. Often, the source of this complaint is fuel leakage into the engine. A misfiring injector allows fuel to wash into the crankcase. A low-pressure, fuel-system jumper tube beneath the valve cover or a high- pressure tube for a common rail injector can quickly leak fuel into the engine. Leaking injector O-rings, which are caused by loose injectors or cut injector O-rings, cause fuel to flow from around the injectors and onto the deck of the cylinder head. UV dyes can be used to inspect for fuel system leaks. However, visual inspection of fuel lines when the engine is running is the most common technique used to identify internal fuel system leaks. Remember, a technician should never use their hand to check for leaks because fuel under high pressure can easily penetrate skin and cause blood poisonin

When checking the engine oil level, the acceptable oil level range is stamped on the oil dipstick Figure 61. An excessive oil level will cause the oil to foam when it contacts the crankshaft or simply leak out of the engine through the rear main oil seal located at the end of the crankshaft Figure 62. High oil consumption complaints need to be verified by an actual measurement of oil used for a given distance Figure 63. Usually the technician diagnosing the complaint, and not the customer, will add oil to the engine in order to provide a verifiable and accurate record for oil consumption.

FIGURE 10-61: The oil dipstick measures the engine’s oil level. The acceptable level is between the MAX and MIN markings.

FIGURE 10-62: The rear main seal of the engine prevents oil from leaking out of the crankcase from around the end of the crankshaft.

FIGURE 10-63: High oil consumption diagnosis process.

1.1. Oil Level Sensors

Oil Level Sensors

Oil level sensors are used to alert the operator to low oil levels. One sensor type can use ultrasonic sound waves to monitor the oil level in the oil pan during the brief initial key on, engine off (KOEO) period. The sensor monitors the correct engine oil level to avoid an overfill or a low oil level while driving or at KOEO. Typically, the sensor is mounted on the bottom of the oil pan and has a piezoelectric transducer that sends ultrasonic sound pulses into the oil. Wave reflection at the oil surface and then back to the sensor measures the time the echo is received from the oil level surface to calculate the distance and hence the oil level (Figure 64 and Figure 65) .

FIGURE 10-64: An oil level sensor uses ultrasonic sound waves that reflect back from the surface of the oil level in the oil pan.

FIGURE 10-65: Location of an oil level sensor and connector on a 6.6 L Duramax oil pan.

Locating an Oil Leak

Quickly and accurately pinpointing oil leaks is an important skill a technician needs to develop. Engine oil leaks are an offense under environmental and Federal Motor Carrier Safety Administration (FMCSA) legislation. An oil leak qualifies as an out-of-service criterion and is strictly enforced in many jurisdictions. Leaks can often be identified by the color of the leaking fluid. Diesel lubricating oil is black while transmission fluid, antifreeze, power steering fluid, and washer fluid can be red, green, gold, orange, brown, or blue. Once a leaking fluid is determined to be engine oil, it can be difficult to identify where it is leaking from because of gravity, air blown across the engine, and the creeping of oil along an edge of a component. The best method to use to identify the location of an oil leak is tracing dye, which is easily detected with a UV light. To locate an oil leak, follow the steps in Skill Drill 10-2.

1.2. SKILL DRILL 10-2  Locating an Oil Leak

STEP 1 Obtain the correct type of fluorescent tracing dye. Some dyes are only compatible with oil, fuel, coolant, or refrigerant. Choose the correct type. STEP 2 Bring the engine to operating temperature and add the prescribed amount of dye to the engine oil as recommended by the dye manufacturer. STEP 3 Road test the vehicle with the engine under load. When checking for a leak, it is important to get the engine oil to operating temperature. High oil pressure and hot oil will reveal leaks quicker than low oil pressure and cold oil. STEP 4 After running the engine for 20–40 minutes, shut the engine off and examine the engine using a UV light. Some kits use alligator clips to power compact, 12-volt lights. The newest dyes reflect a bright yellow-green color at a leak path under UV light. The use of glasses with yellow lenses further enhances the appearance of the dye, making even small leaks easier to detect in tight spots. STEP 5 If uncertain about the actual spot leaking, clean the area with an aerosol solvent and recheck the area with the engine running. STEP 6 Record your observations and make a repair recommendation based on your findings.

1.3. Replacing a Rear Main Oil Seal

Replacing a Rear Main Oil Seal

Engine gaskets and seals are designed to keep liquids, such as oil, from leaking between component surfaces. One particularly important seal is the rear main oil seal located at the end of the crankshaft behind the flywheel Figure 66. This dynamic seal, which is a type of seal that prevents leakage around moving parts, blocks oil from leaking from the crankcase. It surrounds the rear snout of the crankshaft and is located in front of the flywheel, pressed into the flywheel housing Figure 67.

FIGURE 10-66: The seal surface for the rear main seal on this DD15 engine is not on the crankshaft, where seals commonly are, but is instead on the flywheel. The seal should be replaced anytime the flywheel is removed.

FIGURE 10-67: A leaking rear main oil seal. The flywheel is removed.

The seal can begin to leak as a result of wear, excessive bearing clearances, abrasive dirt, or even metal filings in the crankcase, which quickly tear up the seal’s soft materials. Because the seal sits just above the crankcase oil level, even a small amount of seal wear can allow a significant amount of oil to leak out into the housing and onto the clutch or torque converter. Oil covers the underside of a vehicle when the seal is leaking and can even allow the engine to lose most of its oil in a single trip.

To replace a rear main oil seal, follow the steps in Skill Drill 10-3. This procedure is generally performed on an as-needed basis and is not a part of any service recommendation or overhaul procedure.

1.4. SKILL DRILL 10-3  Replacing a Rear Main Oil Seal

STEP 1 Verify that the rear main seal is leaking. If it is, oil will originate from inside the flywheel housing. This should not be confused with an oil pan leak or other engine leaks, which end up dripping from outside the flywheel housing. A fluorescent dye can be added to the engine oil to help easily pinpoint the source of any oil leak. STEP 2 Disconnect and remove the transmission, clutch, and flywheel. STEP 3 Ensure that the flywheel and bell housing are centered by performing the “Reinstalling a Flywheel Housing” Skill Drill in Chapter 8: Cylinder Blocks, Crankshafts, and Engine Bearings. An improperly centered flywheel or bell housing will cause premature wear on one side of the seal. Correct any flywheel runout before removing or reinstalling the new rear main seal. STEP 4 Remove the old seal using a heel bar to pry on a self-tapping screw installed in the seal. STEP 5 Remove any seal wear ring installed on the crankshaft, which most manufacturers use on HD diesels. STEP 6 Inspect the crank sealing surface for damage and clean up the seal surface with crocus cloth. STEP 7 Clean the seal bore in the bell housing. STEP 8 Place a pry bar between the crankshaft and the bell housing to gently pry up on the crankshaft to observe whether there is any visible movement of the crankshaft that would indicate excessive bearing wear. There should be no movement detected. Take special precautions to prevent damaging the crankshaft with the pry bar. Any detectable vertical movement of the crankshaft requires a main bearing replacement and further investigation regarding the remaining service life of the engine. Any movement causes the seal to prematurely wear and leak. STEP 9 Mount the seal on the seal driver using the OEM-prescribed seal installation tool and follow any special instructions recommended by the OEM. STEP 10 Center the seal driver on the end of the crankshaft and set the seal to the correct depth required by the OEM. (This is usually achieved as a feature of the installation tool’s design.) Install a wear ring at the same time as the seal. Use special care to drive the seal into the bore squarely because gravity will tilt the driver and seal and cause damage to both if the seal is misaligned while tightening it into the bore. STEP 11 Clean, reinstall, and torque the flywheel. Run the engine and check for oil leakage from the rear main oil seal.