DTC DTC Preventive Maintenance and Service Intervals 2 — Questions and Answers
Question 1: What should a diesel technician check when performing a coolant service to prevent liner cavitation erosion?
- Engine oil viscosity rating
- Supplemental coolant additive (SCA) concentration levels (Correct answer)
- Fuel filter restriction
- Battery cold cranking amps
Correct answer: Supplemental coolant additive (SCA) concentration levels
SCA concentration must be maintained within specification to protect wet cylinder liners from cavitation erosion caused by pressure wave vibration.
Question 2: A diesel truck's serpentine belt shows glazing and minor cracking. What is the correct maintenance action?
- Apply belt dressing and continue service
- Replace the belt before it fails, per manufacturer interval (Correct answer)
- Increase belt tension to compensate for wear
- Clean with solvent and reinstall
Correct answer: Replace the belt before it fails, per manufacturer interval
Glazing and cracking indicate belt degradation; replacement before failure is the correct preventive action to avoid roadside breakdowns.
Question 3: How often should diesel fuel filters (primary and secondary) typically be replaced on a heavy-duty truck?
- Every 500 miles
- According to the manufacturer's maintenance schedule, often every 15,000–25,000 miles (Correct answer)
- Only when black smoke is observed
- Once per year regardless of mileage
Correct answer: According to the manufacturer's maintenance schedule, often every 15,000–25,000 miles
Diesel fuel filter replacement intervals are specified by the manufacturer and typically fall between 15,000 and 25,000 miles to protect injectors from contamination.
Question 4: When lubricating fifth-wheel assemblies during preventive maintenance, which type of lubricant is typically recommended?
- Motor oil SAE 10W-30
- Multi-purpose chassis grease or fifth-wheel grease (Correct answer)
- Automatic transmission fluid
- Penetrating oil spray
Correct answer: Multi-purpose chassis grease or fifth-wheel grease
Fifth-wheel assemblies require heavy-duty multi-purpose grease designed to withstand high loads and resist washout from road conditions.
Question 5: What is the main purpose of checking and adjusting diesel engine drive belt tension during preventive maintenance?
- To reduce turbocharger noise
- To prevent slippage that causes accessory failures and charging system problems (Correct answer)
- To increase fuel economy by 10%
- To prevent exhaust leaks
Correct answer: To prevent slippage that causes accessory failures and charging system problems
Correct belt tension prevents slippage on alternators, water pumps, and air compressors, which would result in component failure or undercharging.
Question 6: A diesel technician notes the engine oil appears milky or foamy on the dipstick during a PM inspection. What does this indicate?
- The engine needs a tune-up
- Coolant contamination of the engine oil, indicating a head gasket or liner O-ring failure (Correct answer)
- Normal condensation in a cold engine
- The oil filter is clogged
Correct answer: Coolant contamination of the engine oil, indicating a head gasket or liner O-ring failure
Milky or foamy oil is a clear sign of coolant mixing with engine oil, which requires immediate investigation of head gaskets, liner O-rings, or oil cooler integrity.
DTC DTC Preventive Maintenance and Service Intervals 2
What should a diesel technician check when performing a coolant service to prevent liner cavitation erosion?