What causes no compression in a car engine UK?

No compression in a UK car engine is typically caused by valve leakage, excessive piston/ring-to-cylinder clearance, or a blown head gasket. The most common issues affecting popular UK models like the Ford Fiesta, Vauxhall Corsa, or MINI Cooper include:

Valve leakage: Worn, burnt or bent valves lose sealing ability, reducing compression - particularly problematic in high-mileage vehicles.

Excessive clearance: When piston rings or cylinders wear beyond tolerances (common in older petrol/diesel engines), compression drops significantly.

Blown head gasket: A failed gasket between cylinder head and block (frequent in overheating incidents) causes compression loss between cylinders or into coolant passages.

For accurate diagnosis, UK motorists should use a compression tester (available at Halfords) or consult a qualified mechanic, as driving with low compression can cause further engine damage and potentially fail MOT emissions tests.