Engine Systems: Lubrication, Cooling, and Fuel
Engine Systems: Lubrication, Cooling, and Fuel
This domain tests lubrication quality and pressure, cooling-system integrity and temperature control, and fuel delivery. The exam expects a sequence: verify the complaint, inspect the simple items, then test with gauges or scan data.
Core rules
- Use the oil grade and specification in the owner or workshop manual; viscosity alone is not enough. Check level with the engine off and the vehicle level, and replace the filter at the specified interval.
- Low oil pressure warning is not cured by a thicker oil. Confirm with a mechanical gauge, check the pickup, filter, and relief valve, and investigate bearing clearance if pressure is low when hot.
- Use the specified coolant type; mixing silicate, OAT, and HOAT chemistries can cause gel or corrosion. Pressure-test cold, inspect the cap, hoses, thermostat, and fan control.
- Fuel leaks are a fire risk. Relieve pressure before opening lines, use flare-nut wrenches, replace seals, and check pressure and delivery against specification.
Worked example
An engine overheats at idle but is normal at road speed. First check cold coolant level and pressure-test the system. If the electric fan does not run at operating temperature but runs when the A/C is switched on, the fault is likely in fan control: fuse, relay, coolant temperature sensor signal, or fan module. At road speed, ram airflow hides the fault, so replacing the thermostat first is a guess. Confirm the temperature signal with scan data before condemning parts.
Traps
Opening a hot radiator cap, mixing coolant types, overfilling oil, using stop-leak as a repair, and diagnosing fuel pressure from a smell rather than a gauge. Also, do not assume a new filter fixes low oil pressure.