Toyota 1AZ-FE / 1AZ-FSE

Toyota's 2.0 AZ four — in the Camry, RAV4 and Avensis.

It is the 2.4 2AZ-FE's smaller sibling and shares its architecture, which is the most useful thing to carry into a diagnosis — including the part that is bad news.

⚑ The stripped head-bolt threads that made the 2AZ famous are an AZ-family pattern. The aluminium block's threads pull, the head gasket then leaks, and the repair is a thread insert rather than a gasket. A coolant loss with no external leak on an AZ engine is this until proven otherwise, and diagnosing it as a gasket alone produces a repair that fails again.

Oil consumption at high mileage is the other family trait, from the piston rings, and it is common enough to be expected rather than alarming.

The 1AZ-FSE is direct-injected and behaves differently: intake valve carbon accumulates because no fuel washes over them, and a rough idle or a misfire at mileage is a cleaning question before it is anything else. The extra letter is the only place that is written down.