Lubrication, cooling and fuel systems
Lubrication, cooling and fuel systems covers how an engine is lubricated, held at working temperature and supplied with a combustible mixture, and how faults in each system show up.
Lubrication
A gear or rotor pump draws oil from the sump through a strainer, pushes it through the filter and galleries, and a relief valve limits pressure. Multigrade oil such as 10W-40 flows in cold starts and protects when hot; the API or ACEA rating matters as much as viscosity. Low oil pressure shows as a warning lamp or gauge drop and can mean low level, wrong grade, worn pump or worn bearings.
Cooling
Coolant circulates from the water pump through the block and head to the radiator; the thermostat stays closed until about 82–90 °C, then opens. A pressure cap raises the boiling point, and a 50/50 glycol mix gives antifreeze and corrosion protection. Overheating causes include low coolant, a stuck thermostat, a failed fan, a blocked radiator or a slipped belt.
Fuel
Petrol engines need roughly 14.7:1 air–fuel by mass for complete combustion; diesel runs lean, about 14.5:1 stoichiometric but far leaner in practice. Carburettors meter fuel by venturi vacuum; electronic fuel injection times injector pulses from sensor data and runs at high pressure.
Worked example. An engine uses 0.6 kg of petrol per minute. Stoichiometric air = 0.6 × 14.7 = 8.82 kg/min. If the intake actually supplies 8.00 kg/min, AFR = 8.00 ÷ 0.6 = 13.3:1, which is rich.
Traps
Opening a hot radiator cap. Running water only. Overfilling oil. Using the wrong viscosity. Assuming a rich mixture gives more power.