Toyota 5AR / 6AR

The later members of Toyota's AR family — the 2.5-litre 5AR-FE and the 2.0-litre direct-injected 6AR-FSE — sitting between the 2AR that preceded them and the Dynamic Force engines that replaced them.

They are transitional engines, and that is the most useful framing: the 5AR is essentially a market-specific 2AR variant with the same undramatic profile, while the 6AR-FSE introduced direct injection with port injection alongside it (D-4S), which is why it does not accumulate the intake-valve carbon that a direct-injection-only engine of the same period would.

Neither has a documented systemic failure. The recurring items at mileage are the water pump, ignition coils and the variable valve timing actuator — the same short list that applies to most of Toyota's naturally aspirated fours, and a reminder that on this manufacturer a fault is usually a component rather than a pattern.