1HZ engine problems: what wears out, and what an aftermarket turbo changes

Is the 1HZ a reliable engine?

By reputation, yes. It is a 4.2 litre six-cylinder diesel with no factory turbo, a mechanical injection pump and a simple layout, and it was used in the LandCruiser 70 Series, 80 Series, 105 Series and some Coaster buses. Many are now well past 400,000 km, so the problems you see are mostly wear and how the vehicle has been treated.

What problems are reported with the 1HZ?

• Cracked heads, in small numbers. A few heads crack near the pre-combustion chambers.
• Head gaskets after overheating. The gasket is generally fine unless the engine has been overheated.
• Timing belt. Trouble-free if it is changed about every 100,000 km. A belt that is skipped or forgotten is a risk on any belt engine.
• Injection pump. It may need an overhaul at high kilometres, around 400,000 km.
• Big-end bearings. Noted as a weak point on the older LandCruiser diesels, often made worse by poor maintenance.

Does an aftermarket turbo hurt a 1HZ?

It can. The 1HZ is often called slow, especially when towing, so many owners fit a turbo. A well set-up kit with sensible boost and fuelling can work. A poorly set-up one can push exhaust temperatures up, overheat the engine and damage pistons.

If you are buying a turbo 1HZ vehicle, or yours has one, find out who fitted it and how it was tuned. If the old engine died with a turbo on it, that set-up needs checking before a new engine goes in.

What are the warning signs?

The sources we checked do not list symptoms that are special to the 1HZ, so watch for the general ones: the temperature gauge climbing, coolant loss, a new knock, heavy smoke, low oil pressure and a loss of power on hills. If the oil light comes on or a knock starts, stop.

Repair, rebuild or replace?

• Repair for an injection pump, injectors, a belt or a cooling fault caught before it did damage.
• Rebuild your own 1HZ if it is serviceable. We strip it, inspect it and quote a fixed price; if it is not serviceable, there is a teardown fee.
• Replace it with a new long motor when the head, bores or bearings are badly damaged.

What should be fixed before a new 1HZ goes in?

The cooling system, the air intake and filter (dust kills bearings), and the injection pump and injectors, which come across from your old engine. If there is a turbo, its set-up and oil supply. See fitting a new engine and is a new 1HZ engine worth it.

What 1HZ engine does Reco list?

A new 1HZ timed long bare motor for the LandCruiser 75, 78, 79, 80 and 100 Series, listed at $7,950 on 15 October 2026. See the 1HZ engine page.

Ask us about your 1HZ

Use the enquiry form with the LandCruiser's series, year, rego and VIN, and say whether it runs a turbo. Or call 02 9737 0105.