🔍 Key Concepts

• Piston rings and how they seal between the piston and cylinder wall • The path by which fuel and combustion gases might enter the crankcase • Typical causes of crankcase oil contamination in a healthy, normally operating diesel engine

💭 Think About

• Which of these choices describes something that is produced in the cylinders during normal combustion and has a realistic path into the crankcase? • Which contaminants would be present in only small amounts under normal operation versus being the primary contamination source? • Does normal, expected wear create more contamination than what can pass by the piston rings during every power stroke?

✅ Before You Answer

• Focus on what happens at the piston rings during each stroke of the engine • Consider what portion of combustion products could leak past the rings into the crankcase, even in a properly working engine • Ask yourself which option best represents a continuous, ongoing source of contamination during normal operation, not a rare or abnormal condition