Fuel, Lubrication and Cooling Systems
This domain covers fuel delivery, lubrication, and temperature control. The exam expects you to distinguish carburettor, MPFI, and CRDI systems, read oil grades, and explain thermostat and coolant operation.
Core rules
- Petrol engines may use carburettor, port fuel injection (MPFI), or direct injection. Diesel engines commonly use common-rail direct injection (CRDI).
- BS-VI emission control uses precise fuel metering plus catalytic converters, diesel particulate filters, and selective catalytic reduction where applicable.
- Oil grade has two parts: SAE viscosity (for example 15W-40) and API service category. Viscosity describes flow; API category describes performance level.
- Lubrication reduces friction, cools, cleans, and seals. The oil pump, filter, and galleries must maintain pressure.
- Cooling uses coolant circulation, radiator, thermostat, and fan. The thermostat blocks flow until the engine warms up.
Worked example
A thermostat sticks open. The engine warms slowly, heater output is weak, and fuel consumption may rise because the ECU keeps enriching the mixture. Reasoning: coolant flows through the radiator continuously, so the engine cannot reach normal operating temperature. The test is to compare upper-hose temperature with the gauge reading; a thermostat that never closes is confirmed by slow warm-up and low heater performance.
Traps that cost marks
- Confusing SAE viscosity with API service category.
- Mixing different coolant chemistries, which can form sludge.
- Overfilling engine oil and causing aeration or seal leakage.
- Diagnosing overheating without checking thermostat, fan, coolant level, and pressure cap.
- Assuming fuel injection needs no filter service.