Parts for your 2020 Subaru Impreza-Thermostat housing

2020 Subaru Impreza thermostat-housing — what it does, and how to keep it sorted

Yes, the 2020 Subaru Impreza uses a thermostat housing. Technical references that confirm this include the Subaru Factory Service Manual for the 2017–2021 Impreza (Cooling section: Thermostat and Water Pump), which shows the thermostat fitted at the lower radiator hose position within the water pump cover, and Subaru’s official parts catalogue for the 2020 Impreza (Cooling System – Water Pump/Thermostat illustration), which lists the thermostat with an O-ring and a dedicated cover often described as the water inlet/thermostat cover. Trade databases such as ALLDATA and Mitchell 1 also depict the FB20 engine’s thermostat seated in a dedicated housing on the pump side of the engine.

On the 2020 Impreza’s FB20 engine, the thermostat-housing holds the thermostat in the correct position, directs coolant flow from the lower radiator hose, and seals the system with an O-ring. Its job is simple but crucial: help the engine warm up quickly, then regulate coolant flow so it stays in the sweet spot once up to temperature. A healthy housing keeps things leak-free and ensures the thermostat operates as designed.

There’s no fixed replacement interval for the housing itself, it’s typically serviced if it leaks, cracks, warps, or when the thermostat is being replaced. During routine servicing, it’s smart to check for dried coolant traces around the lower front of the engine, any dampness at the housing seam, and condition of the lower radiator hose and clamps. If the thermostat’s being changed, always fit a fresh O-ring and clean the mating surfaces—no sealant unless the service manual specifically calls for it.

Common signs it’s time to look at the thermostat-housing or thermostat include:

• Overheating or taking ages to reach operating temp
• Heater blowing lukewarm air at the lights but hot on the open road
• Coolant weeping around the housing or a sweet smell under the bonnet
• Temperature gauge wandering up and down

When replacing, use quality OEM-spec parts, orient the thermostat exactly as the manual specifies, refill with the correct Subaru long-life coolant, and bleed the system properly to avoid air pockets. Under the bonnet, take care with brittle plastic fittings and hose clamps—after a few years and kilometres they can nick O-rings or crack the housing if overtightened. Don’t crack the cap when it’s hot, and dispose of old coolant responsibly. Do all that and the Impreza’s cooling system will stay happy for the long haul.

Popular questions about the 2020 Subaru Impreza thermostat-housing

Where is the thermostat-housing on a 2020 Subaru Impreza?
It’s mounted at the front of the engine on the water pump side, inline with the lower radiator hose. Subaru’s service and parts documentation shows the thermostat seated in a cover often called the water inlet or thermostat cover.

Should the thermostat-housing be replaced with the thermostat?
Not always. If the housing is sound and not leaking or warped, a new thermostat and O-ring usually does the trick. Replace the housing if there are cracks, persistent leaks, or damaged hose barbs, or if the sealing face is pitted.

What coolant should be used after thermostat-housing work?
Use Subaru-approved long-life coolant premix and bleed the system thoroughly. Correct coolant chemistry and a proper bleed help prevent corrosion, cavitation, and hot spots that can stress the thermostat and housing.