Toyota 2H / 12H-T / 1HD

Toyota's big diesel straight-six — the 4.0 2H and 12H-T and the 4.2 1HZ and 1HD — in the Land Cruiser and Coaster.

These are the engines that gave the Land Cruiser its reputation in places with no dealer network: iron block, slow-turning, mechanically injected on most versions, and repairable with hand tools far from anywhere. That is the design brief, not an accident.

The 1HZ is naturally aspirated and the 1HD is turbocharged, and the difference matters more than the shared displacement suggests — a turbocharged version of an engine designed without one puts the head and the pistons under loads the naturally aspirated one never sees.

Head cracking on the turbocharged engines is the recurring structural item, usually after an overheat or a raised boost setting. Injection pump timing and injector nozzles account for most running complaints, and both drift gradually rather than failing.

The 1VD-FTV V8 that replaced them is a different world and has its own page here.