Parts for your 1998 Mitsubishi Pajero-Thermostat housing

1998 Mitsubishi Pajero Thermostat Housing — what it does and how to look after it

Technical confirmation: The 1998 Mitsubishi Pajero is fitted with a thermostat housing (also called the water outlet or thermostat case). This is shown in Mitsubishi’s Factory Service Manual for 1997–1999 Pajero/Montero models in the Cooling System section, and listed in Mitsubishi’s ASA/CAPS electronic parts catalogue under Engine > Cooling for both petrol (6G72/6G74) and diesel (4M40) engines. Gregory’s and Haynes Pajero manuals for these years also illustrate the housing and gasket in the removal/refit procedures.

The thermostat housing on a ’98 Pajero does more than just hold a thermostat. It forms the gateway between the engine and the top radiator hose, directs coolant flow, and commonly provides mounting for temperature sensors. Built from aluminium, it needs to seal perfectly to the engine with a gasket or O‑ring so the cooling system can pressurise properly. When it’s healthy, the thermostat inside opens at the correct temperature and the housing keeps everything leak-free and flowing the right way.

Owners usually notice housing issues as drips or pink/green crust around the outlet, a sweet coolant smell after shutdown, slow warm-up, or creeping temps under load. Corrosion, pitting where the gasket sits, hairline cracks from overtightened bolts, and warped flanges are the usual culprits—especially on high‑kilometre vehicles or where plain water has been used instead of proper coolant.

As part of regular servicing, it’s smart to give the housing a quick once‑over whenever the coolant is changed (typically every two to four years):

• Check for seepage, staining, or white/green scale around the join and hose neck.
• Run a fingertip over the flange for pitting, any grooves can compromise sealing.
• Inspect hose barbs for nicks and out‑of‑round that can cause weeping under pressure.

If replacing the thermostat or upper hose, consider refreshing the housing gasket/O‑ring at the same time. Clean both mating faces carefully, use a light smear of non‑hardening sealant only if the service info calls for it, and tighten bolts evenly to the specified torque. Always refill with the correct coolant mix and bleed air from the system—watch the heater performance and the temp gauge on the first test drive.

For Pajero engines, stick with the thermostat temperature rating specified for the engine code (common ranges are mid‑70s to low‑80s °C). If the housing is cracked, heavily pitted, or distorted, replacing the unit is cheap insurance against roadside dramas and head‑gasket headaches. Done right, the cooling system will stabilise quickly, warm‑up will be crisp, and the fan won’t have to work overtime on hot Aussie or Kiwi summer climbs.

FAQs

Where is the thermostat housing on a 1998 Pajero?
On most V6 models (6G72/6G74), it sits at the front of the engine where the upper radiator hose connects, near the timing cover. On the 4M40 diesel it’s mounted at the engine side where the top hose meets the head/water outlet casting. If you follow the upper radiator hose back to the engine, you’ll land on the housing.

Do I need sealant when refitting the housing?
Many Pajero housings use a paper gasket or an O‑ring. If it’s an O‑ring style, fit it dry with a touch of coolant-safe lubricant. If it’s a paper gasket, a thin smear of non‑hardening sealant can help—only if recommended for your engine. Clean faces, correct torque, and proper coolant bleeding matter more than goop.

What thermostat temperature should I use?
Use the rating specified for your engine code. Pajero engines of this era typically run thermostats in the mid‑70s to low‑80s °C range. Matching the factory spec helps the ECU and fan strategy behave correctly and keeps fuel economy and heater performance where they should be.