Fuel, Lubrication and Cooling Systems
Fuel systems
Petrol engines mix fuel and air at a stoichiometric ratio of about 14.7:1 by mass; diesel engines run lean and control power by injected quantity. Carburettors use venturi depression and jets; fuel injection uses sensors and an ECU for precise delivery. Common rail diesel uses very high injection pressure. Traps: confusing rich and lean symptoms, and forgetting that a clogged air filter enriches the mixture.
Lubrication
Engine oil reduces friction, cools, cleans and seals. Viscosity grades such as 10W-40 indicate cold (W) and hot behaviour; lower W means better cold flow. Oil pumps are usually gear or rotor type; the filter bypass valve maintains flow when the filter clogs. Low oil pressure can result from low level, worn pump, blocked pickup or excessive clearance. Traps: overfilling (aeration and seal damage) and using the wrong grade.
Cooling
Pressurised systems raise the boiling point; the thermostat regulates flow; the radiator dissipates heat; the water pump circulates coolant. Overheating causes include low coolant, failed thermostat, blocked radiator, faulty fan or slipping belt. Never open a hot pressurised cap.
Worked example: coolant at 50 percent glycol boils near 106 degrees Celsius at atmospheric pressure and higher under a 1 bar cap. Rule of thumb: diagnose overheating by checking coolant level, belt tension, thermostat operation and fan operation in that order.