4N15 Cylinder Head Failure — Symptoms, Causes & Replacement Options (Mitsubishi Triton & Pajero Sport 2.4L)

4N15 Cylinder Head Problems — What Mitsubishi Triton & Pajero Sport Owners Need to Know

The 4N15 is Mitsubishi's 2.4-litre four-cylinder turbo diesel, fitted to the Mitsubishi Triton MQ and MR (2015–present) and Pajero Sport QE and QF (2016–present). It's a modern, capable engine — but as these vehicles accumulate kilometres, cylinder head failures are becoming increasingly common. If you're seeing the warning signs, this guide will help you understand what's happening and what your options are.

Common Symptoms of 4N15 Cylinder Head Failure

  • White smoke from the exhaust — coolant entering the combustion chamber is the most common sign of a blown head gasket or cracked head. Often worse on cold starts and at idle.
  • Coolant loss with no visible external leak — regularly topping up the overflow bottle with no puddle under the vehicle usually means coolant is being burned internally.
  • Overheating — a warped or cracked head disrupts coolant flow. If the temperature gauge climbs, pull over immediately — continued driving will cause catastrophic engine damage.
  • Milky or frothy oil — coolant mixing with engine oil produces a creamy residue on the dipstick or under the oil cap. This is serious and requires immediate attention.
  • Loss of power or rough running — a compression leak across a failed gasket reduces cylinder pressure, causing misfires and sluggish performance under load.
  • Bubbling in the coolant reservoir — combustion gases entering the cooling system cause visible bubbling when the engine is warm.
  • Rough idle or vibration — a failed cylinder is often noticeable as an uneven idle, particularly at low RPM or when the engine is cold.

Why Does the 4N15 Head Fail?

  • Head gasket failure — the 4N15 has developed a reputation for head gasket issues, particularly on higher-kilometre examples and vehicles used for towing or heavy work. The aluminium head is susceptible to warping if the engine overheats.
  • Overheating events — a single overheating event can warp the aluminium head. Even a brief overheat that doesn't result in a breakdown can cause enough distortion to fail the gasket later.
  • Age and kilometres — failures are increasingly common on MQ Tritons and QE Pajero Sports as they pass the 150,000–200,000km mark, particularly those used for towing or off-road work.
  • Coolant neglect — degraded coolant loses its corrosion inhibitors, leading to internal corrosion and pitting on the head surface over time.
  • Timing chain wear — the 4N15 uses a timing chain, and chain stretch on high-kilometre engines can affect valve timing and put additional stress on the head.

Replacement Options

When your 4N15 head fails, you have several paths depending on your budget and how quickly you need the vehicle back:

  • Complete cylinder head — a new head, fully assembled with valves, springs, camshafts and seals fitted, supplied with VRS gasket set and head bolts. Everything needed for a complete replacement in one order.
  • Reconditioning your original head — if the casting is not cracked, a machine shop can reface and recondition your original head. However, given the cost of labour on the 4N15, a new complete head is often the more cost-effective long-term option.

What You'll Need for a 4N15 Head Replacement

A complete 4N15 cylinder head replacement typically requires:

  • Complete cylinder head (assembled with valves, camshafts and seals)
  • VRS head gasket set with new head bolts
  • Timing chain kit — strongly recommended while the front of the engine is accessible
  • Water pump with housing — replace at the same time
  • Timing cover and oil pump — inspect and replace if worn or leaking

The 4N15 has a complex front-end layout with the timing chain, water pump, and oil pump all accessible during a head replacement. Replacing these components at the same time is strongly recommended — the labour overlap makes it cost-effective, and these components are often due at the same interval on high-kilometre engines.

Shop 4N15 Parts

We stock a comprehensive range of 4N15 cylinder head parts, dispatched Australia-wide with free delivery.

All parts come with a 12-month unlimited-kilometre warranty. Pickup available in Bellevue, Perth (6 Edward Street) or fast dispatch from Melbourne. Call us on 0406 611 288 if you need help identifying the right parts for your vehicle.

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