Parts for your 2009 Subaru Exiga-Thermostat

2009 Subaru Exiga thermostat — what it does, where it is, and when to replace it

Yes, the 2009 Subaru Exiga uses a conventional engine coolant thermostat. This is confirmed by Subaru’s factory service information for the Exiga YA series (Cooling System section) and the Subaru FAST parts catalogue for YA5 models, both of which show a wax‑pellet thermostat and gasket fitted at the engine’s water outlet/thermostat housing on EJ‑series petrol engines used in the Exiga. Those references specify the thermostat’s role in regulating coolant flow and identify it as a replaceable service part.

On a 2009 Exiga, the thermostat is essentially the traffic controller for engine temperature. When the engine is cold, it stays shut so the coolant circulates within the block, helping the engine warm up quickly and efficiently. Once operating temperature is reached, it opens to let coolant flow through the radiator, keeping temps stable while you’re cruising, towing, or idling in traffic. That steady temperature protects head gaskets, maintains good cabin heater performance, and keeps fuel economy on song.

While the thermostat isn’t a scheduled replacement item, it’s smart to treat it as preventative maintenance when doing bigger cooling system jobs. Many workshops in Australia and New Zealand will replace it proactively during a timing belt and water pump service on EJ‑powered Exigas, or any time there’s been overheating, sludge contamination, or a radiator replacement. Always use a genuine‑spec thermostat and a new gasket or O‑ring, and refill with the correct Subaru coolant blend. Air bleeding is crucial on Subarus—fill via the header tank and burp the system properly to avoid trapped air that can cause erratic temps.

• Typical warning signs: slow warm‑up or temp gauge wandering, cabin heater blowing cold at idle, fans running constantly, or overheating under load.
• Good service habits: inspect hoses and clamps, check for leaks at the thermostat housing, keep the radiator cap in good nick, and replace coolant at the intervals in the service schedule.
• When replacing: note the thermostat’s orientation (jiggle pin position if applicable), clean the mating surfaces, torque housing bolts evenly, and verify fan operation after bleeding.

If the Exiga’s been running hot or oddly cool, or if the heater’s inconsistent, a sticky thermostat is high on the list. Given the low cost of the part versus the risk of overheating, replacing it during related cooling work is a fair bit of cheap insurance.

FAQs

Where is the thermostat on a 2009 Subaru Exiga?
It’s mounted in the thermostat housing at the front of the engine, where the lower radiator hose connects to the water pump area. Access is from underneath or from the front once the engine under‑tray is off. The housing contains the thermostat and a sealing gasket or O‑ring.

What are the symptoms of a failing thermostat on an Exiga?
Common clues include the temperature gauge creeping higher than normal, fluctuating temps on hills or in traffic, very slow warm‑up, poor heater output, or coolant being pushed into the overflow bottle. A stuck‑closed thermostat tends to cause overheating, while a stuck‑open one causes the engine to run too cool.

Should the thermostat be replaced with the timing belt and water pump?
It’s not mandatory, but it’s widely recommended. On EJ‑engine Exigas, many techs replace the thermostat as part of the timing belt/water pump service to reset the whole cooling system at once. It’s inexpensive, reduces the chance of future cooling issues, and saves doubling up on labour later.