Parts for your 1991 Mitsubishi Pajero-Thermostat housing

1991 Mitsubishi Pajero thermostat housing: what it does and how to look after it

Technical sources confirm that a thermostat housing is absolutely fitted to the 1991 Mitsubishi Pajero. The Mitsubishi Motors Workshop Manual for Pajero/Montero (Group 14 – Cooling System) and period repair guides such as Gregory’s and Haynes manuals describe the thermostat and its housing (often called the water outlet/inlet) on both the 2.5-litre 4D56 turbo‑diesel and the 3.0‑litre 6G72 V6. The Mitsubishi ASA electronic parts catalogue for the V10/V20 series likewise lists the thermostat housing and associated gasket/O‑ring for these engines.

On a 1991 Pajero, the thermostat housing is the metal elbow or cover that clamps the thermostat in place and routes coolant between the engine and radiator. Beyond simply holding the thermostat, it also forms part of the bypass circuit and often carries the coolant temperature sender. On the 4D56 diesel the housing sits at the front of the cylinder head where the top radiator hose attaches, on the 6G72 V6 it’s mounted at the front of the engine at the hose connection to the water pump side.

As part of routine servicing, it’s smart to inspect the housing whenever coolant is changed (typically every 2 years or 40,000–50,000 km, or per the workshop manual). Look for crusty white/green deposits, dried coolant tracks, staining, or a weep around the gasket or O‑ring. Corrosion or pitting on the hose neck, a warped flange, or perished rubber are all cues for replacement. Temperature swings, slow heater performance, or a coolant smell under the bonnet can also point to issues around the housing or thermostat.

Replacement is a straightforward DIY for a competent home mechanic. Allow the engine to cool fully, drain enough coolant to drop the level below the housing, then remove the radiator hose and the housing bolts. Clean both mating faces carefully without gouging the alloy. Fit a new thermostat and the correct gasket or O‑ring, using only the sealant specified by the manual if any. Refit the housing and tighten the fasteners evenly to factory torque. Reconnect the hose, refill with the correct Mitsubishi‑approved coolant mix (check your climate, many owners in Australia and New Zealand run a 33–50% ethylene glycol mix), then bleed the system to purge air.

Preventative tips that pay off off‑road and on the open road:

• Refresh coolant on schedule, old coolant accelerates corrosion in alloy housings.
• Replace the radiator cap if it’s tired, poor pressure control encourages leaks.
• Check hoses and clamps so they don’t chew the housing neck or weep under load.

Done right, a fresh thermostat and sound housing keep the Pajero running at the right temperature, whether it’s towing up the Kaimais or cruising the Stuart Highway.

FAQs

Where is the thermostat housing on a 1991 Pajero?
On the 4D56 turbo‑diesel it’s at the front of the cylinder head where the upper radiator hose meets the engine. On the 6G72 V6 it’s at the front of the engine where the radiator hose connects near the water pump. Following the relevant hose from the radiator will lead straight to the housing.

What are common signs the housing or thermostat needs attention?
Look for coolant seepage, chalky deposits, or staining around the housing, fluctuating temperature gauge readings, a heater that’s slow to warm, or an overheating episode. Any corrosion on the hose neck or a warped sealing face is a good reason to replace the housing with the thermostat and gasket/O‑ring.

Do I need sealant when refitting the housing?
Most Pajero engines use a dedicated paper gasket or an O‑ring. If a gasket is specified, fit a new one dry or with the recommended non‑hardening sealant only if the workshop manual calls for it. Avoid excess sealant, as squeeze‑out can break loose and circulate through the cooling system.