Some 1999-2008 Impreza and Forester, 2000-08 Legacy and Outback, and 2006-08 Tribeca models may lose large amounts of antifreeze from the coolant reservoir.
One likely cause, Subaru said, is a stuck negative pressure valve in the radiator cap.
The valve sticks due to debris at the bottom of the reservoir being sucked up through the coolant hose as the cooling system cools. Cleaning the cap and reservoir and modifying the hose should eliminate the coolant loss.
Begin the fix by removing the radiator cap. Now turn the cap over, open the negative pressure valve with a small flat-bladed screwdriver.
Use a stiff brush and tap water to clean the sealing surface of the valve. Pressure test the cap to be sure it's within specification, then lay the cap aside.
Next, remove the reservoir and flush it several times with clean water. Reinstall the reservoir, then fill with coolant to the full mark.
Now go to the coolant hose and cut about ¾ of an inch from the end at a 45-degree angle. Reinstall the hose and the pressure cap.
To complete the fix, start the engine, let it reach operating temperature, shut it down, let the system cool, then add coolant to the reservoir, as necessary.
"Factory Fixes" is written by Jim DePalma, a 30-year veteran of the auto repair business who has served stints as a service manager, parts manager and ASE-certified technician. His column provides vehicle manufacturers' authentic factory technical service bulletins (TSBs) that have been condensed for easier reading. Mr. DePalma advises that techs always check with a dealer or repair information system for the latest revisions before starting to work on a vehicle. He can be reached via e-mail at [email protected].