I am a long time Amsoil filter user and now a dealer. The oil filter part # is SDF20 for ALL models and engines of Subaru from 1997 to 2000 (at least, since that is what my wife and I have). If you have different years, you can call or e-mail them (or me) for confirmation. The bi-pass valve needs to activate at the correct pressure to avoid engine damage. Amsoil's does. Amsoil filters exceed the capacity AND filtration cababilities of Mobil 1, WIX, FRAM, AC, Purolator, NAPA and the now discontinued HardDriver. The micron bi-pass filter (used in addition to a SDF filter) is in a class by itself.
The AMSOIL Super Duty Oil Filter (SDF) is designed to provide maximum filtration while meeting the high flow demands of modern automobiles. The AMSOIL SDF contains a special cellulose, synthetic and glass blend media that offers the best possible balance of long life, high capacity and overall efficiency.
Traps Dirt Throughout Media Thickness
The AMSOIL SDF has a lofted fiber depth-type media that traps dirt throughout its entire thickness for exceptional filtering efficiency. It keeps oil clean and free of wear-causing contaminants. The AMSOIL SDF Oil Filter provides up to 100 percent more capacity and up to 20 percent greater efficiency than other filters provide. It is ideal for use with extended oil drain intervals.
Built for Rugged Performance
The AMSOIL SDF has a heavy-duty case of drawn steel. The case is double-crimped at the base with rolled-under seaming to withstand extreme pressure surges and road shocks.
Assures Oil Flow with Relief Valve
On most filters a relief valve is provided to assure ample oil flow. It prevents oil starvation in the engine in the event the media becomes saturated.
Prevents Oil Drainage During Engine Shutdown
On filter installations where the mounting is sideways or upright, dirty oil could drain out of the filter when the engine is shut off. The AMSOIL SDF has an anti-drainback valve that keeps trapped contaminants in the filter when the engine is not running.
AMSOIL INC. recommends changing the AMSOIL SDF according to the following guidelines.
In gasoline-fueled engines using any AMSOIL motor oil except AMSOIL XL-7500 Synthetic Motor Oil, change the filter at 12,500-mile or six-month intervals. In gasoline-fueled engines using AMSOIL XL-7500 Synthetic Motor Oil, change the filter at 7,500-mile or six-month intervals. If a Hastings or other filter is used, filter should be changed at manufacturer recommendations.
When using an AMSOIL Oil Filter with conventional motor oils, refer to the owner's manual for the recommended oil filter change interval.