Parts for your 1999 Mitsubishi Pajero-Thermostat

1999 Mitsubishi Pajero Thermostat — What it does and when to replace

Yes, the 1999 Mitsubishi Pajero uses a thermostat. This is confirmed by Mitsubishi’s factory service manual for the late Gen 2/2.5 Pajero (covering 6G72 3.0L and 6G74 3.5L petrol V6s and the 4M40 2.8L turbo-diesel), the Mitsubishi ASA/CAPS parts catalogue, and common aftermarket catalogues from brands like Gates and Dayco, all of which list an engine coolant thermostat and housing for these variants.

On this Pajero, the thermostat sits in the alloy housing where the lower radiator hose meets the engine—up front on the V6 near the timing cover and on the 4M40 on the front side of the block. Its job is to help the engine warm up quickly and then hold a steady operating temperature (typically in the 82–88°C range depending on engine and market). That stability keeps fuel economy tidy, the heater working well, and emissions in check, while protecting the engine under load.

Owners sometimes wonder about pulling a thermostat to fight overheating—don’t. Deleting it usually leads to over-cooling at speed, sluggish warm-up, higher wear, poor heater output, and even coolant flow issues that can make hot spots worse. If there’s a temperature problem, the thermostat should be tested and replaced if it’s sticking, slow to open, or not sealing.

Good times to fit a new thermostat include any cooling system overhaul, after an overheat event, with a water pump or timing belt job on the V6, or simply as preventative maintenance every few years if history’s unknown. Use a quality OEM-spec unit with the correct temperature rating for your engine code and climate, and always install a new gasket or O‑ring. Many Pajero thermostats have a small jiggle pin or bleed hole—fit it at the top to help purge air.

Replacement pointers under the bonnet: start stone-cold, drain coolant below the housing, remove the housing and old stat, clean mating faces, install the new stat in the correct orientation, and tighten housing bolts to factory spec. Refill with the correct coolant mix (use demineralised water with the right concentrate), run the engine with the heater on hot to bleed air, squeeze hoses, top up the radiator and overflow, then road test and recheck levels. After replacement, they should see steady gauge behaviour and strong heater performance.

• Common signs it needs attention: slow warm-up, fluctuating temp gauge, heater blowing cool, unexplained overheating, or upper hose staying cold then suddenly going very hot.

FAQs

Where is the thermostat on a 1999 Pajero?
The thermostat lives in the alloy housing at the end of the lower radiator hose. On the V6 petrol (6G72/6G74), that’s at the front of the engine by the timing cover. On the 4M40 2.8 turbo-diesel, it’s mounted at the front of the block on the radiator side. Remove the housing to access the thermostat and seal.

What temperature thermostat should be used?
Most 1999 Pajero engines use an OEM-spec thermostat in the low-to-mid 80s °C range. The exact rating depends on engine code and market—commonly around 82°C for the V6, with diesel options varying by climate. Match the factory spec stamped on the original or check a trusted parts catalogue for the engine code.

How often should the thermostat be replaced?
There isn’t a strict kilometre interval. Replace it if there are symptoms or test failures, after overheating, or proactively when doing a cooling system refresh, radiator replacement, or water pump/timing belt service. If service history is unknown, many techs prefer fitting a new stat and seal to avoid surprises.