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

1.3. 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.