Toyota 2AZ-FE

The 2.4-litre member of Toyota's AZ family — aluminium block with cast-iron liners, aluminium DOHC head, VVT-i on the intake camshaft, and the volume petrol engine in Camry, RAV4 and Highlander through the 2000s.

Oil consumption is the pattern fault, traced to piston-ring design on a defined range of production years, and it matters more here than the same phrase does elsewhere: this engine gives little warning. Owners on long service intervals have run them low enough to cause bearing damage without a low-oil light doing anything useful. On any 2AZ of this era, check the level before believing any other diagnosis — a lean code, a misfire and a knock complaint can all be downstream of it.

The second known issue is stripped cylinder-head bolt threads in the aluminium block, which presents as a head-gasket failure that recurs after a conventional repair. A second gasket failure on the same engine is a thread problem until proven otherwise, and needs thread inserts rather than another gasket.