Ford 2.3 EcoBoost

The largest of Ford's four-cylinder EcoBoost engines — the Mustang's entry engine, the Focus RS's, and the powerplant of the Ranger, Bronco and later Explorer.

In the Focus RS it acquired a specific and instructive reputation: head-gasket failures traced to the use of a Mustang cylinder head with different coolant passage sizing, which Ford eventually addressed. It presents as coolant loss and white exhaust smoke, and it is the reason a coolant complaint on an RS is treated differently from the same complaint on a Mustang.

Across applications the general profile is a strong, heavily boosted direct-injection four: intake-valve carbon at mileage, sensitivity to oil condition given turbocharger duty, and — because these engines are very commonly modified — the standing question of what software and hardware the car is running before any knock, boost or misfire code is taken at face value.