Parts for your 2018 Subaru Impreza-Thermostat

2018 Subaru Impreza Thermostat

Based on Subaru’s factory service information (STIS, Cooling System section) and OEM parts catalogue illustrations for the MY2018 Impreza with the 2.0‑litre FB20 engine, this model is fitted with a conventional wax‑pellet engine coolant thermostat. It’s housed in the lower radiator hose inlet at the front of the engine. So yes—there is a thermostat on a 2018 Subaru Impreza, and it plays a key role in keeping the engine right on its ideal operating temperature.

The thermostat’s job is simple but critical: when the engine’s cold, it stays closed to help the motor warm up quickly. Once up to temperature, it opens to let coolant circulate through the radiator, shedding heat and keeping things steady. That sweet spot delivers better fuel economy, lower emissions, a stronger cabin heater, and longer engine life.

For servicing, the thermostat itself isn’t a routine replacement item, it’s typically changed if it fails, shows signs of sticking, or as a preventative swap during major cooling system work. Always use an OEM‑spec thermostat and a new gasket/O‑ring, and refill with the correct long‑life Subaru coolant. Follow the maintenance schedule in the owner’s manual for coolant change intervals, and never mix coolant types.

• Common clues it’s time to check the thermostat: slow warm‑up, overheating, temperature gauge wandering up and down, poor heater performance, or cooling fans cycling oddly.
• Avoid driving without a thermostat—doing so can cause chronic under‑temperature running, higher fuel use, and even engine wear.

Replacement is straightforward for a competent DIYer, though many will prefer a workshop. Expect to drain enough coolant to get below the housing, remove the lower inlet/thermostat housing, swap the thermostat and seal, and reassemble to the correct torque. The cooling system then needs to be refilled and bled properly to remove air. Under the bonnet, access is usually from underneath with the splash shield removed, so axle stands or a hoist make life easier.

After any thermostat or coolant work, a proper bleed, leak check, and a thorough road test with the heater on are essential. Done right, the Impreza will warm up crisply and hold temperature bang on—just as it should.

Popular questions about the 2018 Subaru Impreza thermostat

Where is the thermostat located on a 2018 Subaru Impreza?
On FB20‑equipped 2018 Imprezas, the thermostat sits in the lower radiator hose inlet at the front of the engine, near the water pump area. It’s typically accessed from underneath after removing the engine under‑tray.

What are the symptoms of a failing thermostat on this model?
Drivers might notice slow warm‑up, overheating, fluctuating temperature readings, weak cabin heat, or the radiator fans behaving inconsistently. Any of these warrant a cooling system inspection before bigger issues develop.

Should the thermostat be replaced as preventative maintenance?
It’s not a scheduled item. It’s usually replaced when there are symptoms, during major cooling system service, or if contamination/corrosion is present. Always fit an OEM‑spec thermostat and new seal, and use the correct Subaru long‑life coolant.