Parts for your 2019 Subaru Impreza-Radiator cap

2019 Subaru Impreza radiator cap — what it is, where it lives, and how to look after it

Based on Subaru’s technical documentation (2019MY Impreza Owner’s Manual and the Subaru Service Manual for the FB20 cooling system), the 2019 Subaru Impreza does not have a traditional cap on the radiator neck. Instead, it uses a pressurised cap on the engine-mounted coolant filler tank (sometimes called a header or surge tank). So yes, a “radiator cap” is absolutely relevant and fitted to this vehicle—it’s just not on the radiator itself.

That cap is a small part that does a big job. It seals and pressurises the cooling system so coolant can run hotter without boiling, and it manages expansion and contraction by venting excess coolant to the overflow bottle and drawing it back as things cool down. It also serves as the safe fill point for bleeding and topping up after service. If the cap can’t hold the specified pressure or its valves stick, the Impreza can overheat, push coolant out, or suck hoses flat as it cools.

For servicing, treat the cap like a safety device. Never crack it open hot—wait until the engine is stone cold. Inspect the rubber seals for nicks or flattening, check the spring action, and look for white crust or staining that hints at past leaks. If there’s any doubt, replace it with a genuine or high-quality equivalent with the exact pressure rating shown on the original cap/Subaru specs for the FB20 engine. Avoid “uprating” the pressure, that can stress the radiator, heater core, and hoses.

A good workshop will pressure-test the cap during cooling-system service and coolant changes. As a practical rule, have it checked every service and plan replacement around major cooling work or about every 5 years/100,000 km if condition is unknown. When refitting, clean the filler neck, seat the cap squarely, and twist fully to the second stop so the seal clamps properly.

Watch for classic bad-cap clues:

• Coolant smell, dampness, or dried residue around the filler tank or overflow hose
• Unexplained coolant loss or frequent top-ups
• Overheating in traffic, then cooling at speed
• Upper hose collapsing after shutdown

It’s a cheap, quick fix that protects a very not-cheap engine—well worth keeping in top nick under the bonnet.

FAQ

Where is the radiator cap on a 2019 Subaru Impreza?
It’s on the engine-mounted coolant filler tank, not on the radiator. Look near the top of the engine for the metal or plastic header tank with the pressure cap on top, plus a separate translucent overflow bottle nearby.

What pressure rating cap should be used?
Use the exact rating shown on the original cap and in Subaru’s specs for the FB20 engine. Many caps for this model are around the 1.1 bar range, but the correct choice is the one stamped on the cap or listed for the VIN—don’t up- or down-rate.

How often should the cap be replaced?
Have it inspected at every service and pressure-tested during coolant changes. If its condition is unknown, replacing about every 5 years/100,000 km is sensible, or sooner if there are leaks, weak spring tension, or cooling issues.