The Mitsubishi 4M40 engine was originally designed for the Mitsubishi Pajero off-road vehicle, with an output of 150 PS. It is an automotive diesel engine, featuring a timing chain drive, single overhead camshaft (SOHC), and shim-type valve clearance adjustment.
The original engine was equipped with a Delphi (U.S.) distributor-type fuel injection pump, a pre-combustion chamber, and single-hole injectors, representing the 1970s–1980s level of diesel technology.

This engine is known for its high fuel consumption and poor cold-start performance, but it runs smoothly and quietly—provided that it is the twin balance shaft version.
With a 2.8-liter displacement, the 4M40 is a low-displacement diesel engine, available in naturally aspirated and low-boost turbocharged variants (with different power outputs).
Besides its original use as an automotive powerplant, it is also widely applied as the prime mover in construction machinery, such as 5–8 ton class excavators from Caterpillar and Sumitomo.

Cold Weather Starting Performance

Under proper operating conditions, the 4M40 engine is designed to start normally at ambient temperatures down to –20°C, provided that all systems are in good condition — battery, glow plugs, starter motor, cylinder compression, and fuel delivery.
Any malfunction in these areas — especially within the electrical preheating circuit — will directly affect cold-start performance.

Many operators complain that the 4M40 is hard to start in cold weather, but this is usually due to poor engine condition, not a design flaw.
Even a Rolls-Royce will fail to start if it’s not maintained properly.
(Our company’s Mercedes-Benz service division also sees similar cases where vehicles have to be towed in.)

So, instead of blaming the engine, the key is to diagnose and solve the actual problem.
Complaints won’t help — this engine model is already obsolete, and “criticizing a retired tiger” doesn’t change that.

Recommendations for Operators Experiencing Cold Start Problems

For users struggling with cold starting, it is strongly recommended to visit an authorized Mitsubishi dealer for diagnostic testing and targeted repair.
A roadside repair shop might fix it by luck, but dealers have trained technicians who know the brand’s systems and are generally more reliable — even if some may complain about the cost.

If you have sufficient technical skill, you may perform basic diagnostic checks yourself before deciding on repairs:

Inspection Steps

1. Electrical System Check:
   Ensure all fuses are intact, wiring connections are secure, and glow plugs show no visible damage.
   Remove the oil filler cap and observe for excessive crankcase blow-by under both hot and cold, full-load conditions.
   (Note: This engine uses a closed crankcase ventilation system, with no external breather tube.)
   If the engine is hard to start both hot and cold, that issue is outside the scope of cold-start discussion.

2. Glow Plug Heating Check:
   With the engine ready for start, turn the ignition switch ON, then lightly touch each glow plug to see if it warms up.
   ⚠️ Caution: Do not grasp the glow plug directly to avoid burns — medical expenses are not covered by this organization.

3. Mixed Heating Response:
   If some plugs heat and others don’t, replace the defective glow plugs and retest.
   (It is advised to have a qualified technician perform this, as broken glow plugs during removal — stuck in the cylinder head — are not uncommon.)

4. No Heating at All:
   If none of the glow plugs heat up, consult a professional technician.
   The glow system is controlled by a microcontroller-based module, and without understanding the circuit, you are more likely to make things worse than better — but you’re welcome to try if you insist.

5. Good Glow Plugs but White Smoke During Cranking:
   If all glow plugs are working but thick white smoke appears during cold starting, this usually indicates low cylinder compression, a typical symptom of engine wear.