A Must-Have Oil Upgrade for Subaru FA & FB Engine Longevity

Why Subaru FA & FB Engines Suffer From Oil Drain-Back

If you've owned your Subaru for a while, you may have noticed that familiar clack-clack-clack on cold starts, that brief moment before oil pressure builds and everything quiets down. That's not just "Subaru being Subaru." Subaru FA and FB series engines have inverted oil filters mounted on the top of the engine and suffer from a prolonged dry start due to oil draining from the feed and output side of the oil filter following engine shutdown.

The inverted oil filter maintains a pocket of air compressed at the end of the filter when the engine is running. Following engine shutdown, the air in the filter returns to atmospheric pressure and forces oil out of the filter.
The Baxter Performance Anti-Drain Adapter fixes that problem for good.

What the Baxter Performance Anti-Drain Adapter Does

Baxter's patented anti-drain oil filter adapter contains an out-flow check valve that prevents air from migrating into the oil feed galley from the filter. The adapter installs between your block and the oil filter on Subaru FA and FB engines. Its internal check valve prevents oil from draining back into the pan after shutdown, keeping the filter and upper oil passages full.

That means instant oil pressure on startup and far less wear from those "dry starts" that happen every morning or after the car sits for a few days or even just a few hours.

Why the Factory Anti-Drain Back Valve Isn’t Enough

Don't Subaru oil filters already have an anti-drain back valve? Why do I need this?
Yes, Subaru oil filters include a rubber anti-drainback valve, but on FA and FB engines with a top-mount (inverted) oil filter, that valve alone isn’t enough.

Inside the front engine cover, the oil feed galley from the pump and the oil supply galley from the filter are separated by a metal plate with no gasket sealing the two passages. After the engine is shut off, this allows air to migrate between the galleys, which lets oil drain back through the pump. When this happens, the oil filter’s internal anti-drainback valve is effectively bypassed, even though it is functioning as designed.

The Baxter Anti-Drain Adapter addresses this design limitation by working in conjunction with the oil filter’s internal valves. The filter’s anti-drainback valve prevents oil from draining back down the feed side, while the Baxter adapter’s outflow check valve prevents the supply side from draining. With both sides remaining full of oil, air can no longer migrate between the galleys, keeping the oil system flooded between starts.

Installation: Do You Need to Wait Until Your Next Oil Change?

Nope. One positive of Subaru's top-mounted filter design, you can install the Baxter adapter anytime without dumping your oil. Just remove the filter, add the adapter, reinstall the filter, and you're done. It's a 10-minute mod that pays off every time you turn the key.

Will an Anti-Drain Adapter Affect My Subaru Warranty?

No, however, the dealer may choose not to service an oil/filter change due to the adapter having a Schrader valve and deviating from servicing protocol. Here's more info from Baxter Performance about how their adapters do not void your factory warranty: Baxter Performance Factory Warranty Info

Should You Pre-Fill the Oil Filter? How to Prime Your Subaru Oil System

Not if you prime the oil system correctly. Most owners don't realize 2005 and newer Subarus with drive-by wire throttle bodies have a built-in way to do this called "clear flood mode." This allows you to crank your engine over while disabling both the ignition and fuel systems.

How to Do the Clear Flood Procedure on Your Subaru

For Subaru models with a push-button start:

• Make sure the vehicle is in park or neutral and the parking brake is engaged.
• Press the brake pedal all the way down.
• Press the accelerator pedal all the way to the floor and hold it there.
• Press the start button to begin the cranking process.
• The engine will crank for about 5-6 seconds because the fuel and ignition systems are disabled and then stop on its own or press the button again to stop it.
• Release the accelerator pedal.
• Press the start button again to start the engine normally. 

For Subaru models with a keyed ignition

• Ensure the car is in neutral or park and the parking brake is set.
• Press the accelerator pedal all the way to the floor and hold it there.
• While holding the pedal down, turn the key to the "start" or "on" position and let the engine crank for about 3-4 seconds or until you see the low oil pressure light on the dash go out.
• Release the gas pedal and turn the key to the "off" position, then turn it back to the "start" position to start the engine normally.

Your oil system is now primed! Start it normally and you'll avoid that first-start oil starvation.

What If I Don’t Have an Air Compressor to Clear the Filter?

No worries. Anything that can attach to a Schrader valve will work — a portable tire inflator or even a bicycle pump. Aim for at least 30 PSI (up to 100 PSI) to push out the residual oil when performing a change.

Why This Upgrade Is Essential for Subaru FA & FB Engine Longevity

Subaru's FA and FB engines are known for their reliability, but oil starvation on startup is a long-term wear contributor that most owners overlook. The Baxter Anti-Drain Adapter is one of those rare upgrades that's cheap insurance:

• Extends engine life
• Reduces startup noise
• Improves cold-start lubrication
• Takes minutes to install