Parts for your 1987 Mitsubishi Pajero-Thermostat housing

1987 Mitsubishi Pajero thermostat housing — what it does and how to look after it

Yes, the 1987 Mitsubishi Pajero does use a thermostat housing. This is confirmed across the Mitsubishi Pajero/Montero Factory Service Manual (1983–1991, Cooling System section), the Mitsubishi ASA electronic parts catalogue for the L040 series, and mainstream repair manuals such as the Haynes Pajero/Montero 1983–1997 guide. Whether it’s the 2.6‑litre 4G54 petrol or the 2.3/2.5‑litre 4D55/4D56 diesels, there’s an alloy thermostat housing (also called the water outlet) bolted to the cylinder head, carrying the upper radiator hose and, in many variants, the temperature sender.

The housing’s job is simple but crucial: it locates the thermostat, directs coolant either through the bypass (while the engine warms up) or out to the radiator (once at operating temp), and provides a leak‑free, rigid connection point for hoses and sensors. A healthy housing helps the Pajero warm up quickly, hold steady temps on long Kiwi or Aussie runs, and keeps the cooling system sealed under pressure.

As part of regular servicing, it’s smart to inspect the housing whenever coolant is changed. Look for white or green crust, dampness around the gasket, and corrosion at the hose neck. If the flange is pitted or the neck is cracked, replace the housing rather than trying to nurse it along. Always fit a new gasket or O‑ring and install the thermostat in the correct orientation (jiggle pin up, as noted in the factory manual). Avoid over‑tightening, the alloy can warp or crack—use the service‑manual torque spec and tighten the bolts evenly.

• Work only on a dead‑cold engine and relieve pressure before opening the system.
• Drain coolant below the housing level, remove the upper hose and any sensors, then lift the housing off.
• Clean both mating faces until spotless, no old sealant or gasket should remain.
• Refit with a fresh gasket/O‑ring, use sealant only if the manual calls for it.
• Refill with quality ethylene‑glycol coolant (typically 50/50 with demineralised water) and bleed with the heater on.

On older Pajeros, galvanic corrosion between steel bolts and the aluminium housing is common—use a light dab of anti‑seize on clean threads and replace tired hose clamps. Conventional green coolant usually wants changing about every two years, sticking to that interval does wonders for the housing, thermostat, and radiator lifespan.

Popular questions about 1987 Mitsubishi Pajero thermostat housing

Where is the thermostat housing located on a 1987 Pajero?
On 4G54 petrol models it sits at the front of the cylinder head, forming the elbow for the upper radiator hose. On 4D55/4D56 diesels it’s on the front/right side of the head in a similar spot. It often carries the coolant temperature sender. If you follow the top radiator hose back to the engine, you’ve found it.

What thermostat temperature should be used?
Most 1987 Pajero engines specify around 82°C for the thermostat, with some markets listing an 88°C option. Choice depends on engine code and climate—both are supported in factory literature. Matching the service‑manual spec and using a quality thermostat with the jiggle valve at the top keeps warm‑up and operating temps on point.

What are common leak points and how are they fixed?
Typical culprits are a flattened gasket/O‑ring, corrosion at the hose neck, and weeping sensor threads. The fix is usually a new gasket or housing, fresh hose and clamp, and proper thread sealant for the sender if specified. Clean faces, even bolt tension, and the right coolant mix prevent repeat leaks.