Parts for your 2018 Mitsubishi Asx-Thermostat

2018 Mitsubishi ASX Thermostat — Purpose, care, and when to replace

Referencing Mitsubishi technical sources — specifically the Mitsubishi Motors Service Manual (Cooling System, Group 14) for the GA2W/ASX platform and the Mitsubishi ASA/EPC genuine parts catalogue — the 2018 Mitsubishi ASX is fitted with a wax‑pellet engine thermostat located in the water inlet/housing. It regulates coolant flow to the radiator and is absolutely relevant to the ASX’s petrol and diesel engine variants used in 2018.

The thermostat’s job is to help the engine warm up quickly and then hold a steady operating temperature, typically in the low‑to‑mid 80s °C range. That stable temp keeps fuel economy tidy, emissions low, heater performance strong, and engine wear under control. On the ASX, the thermostat works with a bypass circuit so coolant recirculates within the engine while it’s cold, then opens to the radiator as it reaches its designed opening point.

As part of routine servicing, the thermostat isn’t a fixed-interval replacement item, however, it should be assessed whenever coolant is changed or there are temperature irregularities. During a coolant service, a technician will usually:

• Inspect for leaks around the thermostat housing and O‑ring/gasket
• Check warm‑up time and gauge stability, and scan ECT (engine coolant temp) with a scan tool
• Confirm radiator hose temperature changes as the thermostat opens

Tell‑tale signs a thermostat may be on the way out include running too cool on the motorway (stuck open), slow cabin heat, or — at the other extreme — overheating, a hot lower hose staying cold, and pressure build‑up (stuck closed). Any of these warrant prompt attention to protect the alloy head and head gasket.

When replacement is required, using a genuine or high‑quality equivalent thermostat and a new seal is key. Under the bonnet, the thermostat housing is typically at the end of the lower radiator hose. Replacement involves draining enough coolant, swapping the unit, torquing housing bolts to spec, and refilling with Mitsubishi‑approved long‑life coolant at the correct concentration (often a 50/50 premix). Bleeding air properly — heater on hot, engine at fast idle, top up as the thermostat cycles — avoids hot spots. After a road test, recheck the level once it cools. Disposal of old coolant should follow local environmental rules in AU/NZ.

Looked after this way, the ASX’s thermostat tends to be a fit‑and‑forget part until age, kilometres, or contamination give it grief.

Popular questions about the 2018 Mitsubishi ASX thermostat

Where is the thermostat on a 2018 ASX?
It sits in the water inlet/thermostat housing, typically where the lower radiator hose meets the engine. Access may require removing the air intake duct or an undertray, depending on engine and market spec.

What temperature does the ASX thermostat open?
Most ASX engines of this era use a thermostat that begins opening in the low‑to‑mid 80s °C. The radiator fans are ECU‑controlled and may come on later, so the gauge sitting around the middle is normal.

Is it safe to drive with a faulty thermostat?
Not really. A stuck‑open unit can cause poor fuel economy and weak heater output, while a stuck‑closed unit risks quick overheating and head gasket damage. If symptoms appear, it should be checked before more driving.