Parts for your 1999 Subaru Forester-Radiator cap

1999 Subaru Forester radiator cap — purpose, fitment, and servicing tips

Yes, a radiator cap is used on the 1999 Subaru Forester. Technical sources that confirm this include the Subaru Forester (SF) Factory Service Manual cooling system section, which specifies “Radiator Cap: Inspection” with an opening pressure of approximately 108 kPa (1.1 bar), and Subaru’s parts catalogue listing a pressure cap (commonly P/N 45137AE000, 108 kPa) for SF-series Foresters. General service guides such as Haynes also include radiator cap testing procedures for late-1990s Subaru boxers. On naturally aspirated models, the cap sits on the radiator neck, on turbo GT variants, the pressure cap is fitted to the high-mounted alloy header/filler tank rather than the radiator itself—but it serves the same role.

On a 1999 Forester, the radiator cap does more than just seal the top. It controls cooling system pressure so coolant can run hotter without boiling, helps move coolant between the radiator and overflow bottle as things heat and cool, and keeps air out of the system. When the cap’s spring and seals get tired, it can cause tricky issues—think random overheating on hills, coolant loss with no visible leak, or hoses going rock-hard or oddly soft under the bonnet.

Servicing is straightforward and worth doing as part of regular cooling system care. Stick with the correct pressure rating (around 108 kPa/1.1 bar as per Subaru spec). A quality OEM-equivalent cap is recommended. The cap should only ever be opened when the engine is stone cold. If a pressure tester is available, the cap can be checked for holding pressure and proper vacuum return, otherwise, inspect the rubber seals for cracks, swelling, or flattening, and the valve for smooth movement.

Practical tips owners appreciate:

• Replace the cap every 4–5 years or ~80,000–100,000 km, or sooner if there are cooling quirks.
• Match the cap type to the vehicle layout: radiator neck on non-turbo, header/filler tank on Forester GT.
• After fitting a new cap, monitor coolant level and hose feel over a few heat cycles.
• Use the correct coolant mix and bleed air properly to support the cap’s pressure control.

Getting the humble cap right protects the head gaskets, keeps temps stable in Aussie and Kiwi summers, and saves litres of drama down the track.

FAQs

What pressure radiator cap does a 1999 Subaru Forester use?
Most 1999 Foresters specify a pressure cap of about 108 kPa (1.1 bar, roughly 15–16 psi) as outlined in Subaru’s service info. Sticking with the OEM rating helps keep boiling margins and coolant flow spot on.

Where is the radiator cap on a 1999 Forester?
On non‑turbo models it’s on the radiator neck, visible when the bonnet is up. On turbo GT models, the pressurised cap is on the alloy header/filler tank mounted high in the engine bay, the radiator itself may not have a cap.

How often should the radiator cap be replaced?
As a rule of thumb, replace every 4–5 years or around 80,000–100,000 km. If there’s unexplained coolant loss, overheating under load, or tired seals on inspection, replace sooner and recheck system behaviour.