Replacing A Fuel Filter On A Pressurized System

I’m not sure when the fuel filter in my 95 Subaru Impreza was last changed (I’d guess maybe at 90,000 miles, if it’s ever been done). I hope it’s been done in the past as it’s a fuel-injected engine. I could probably do it myself, but what worries me is that it’s a pressurized system. It seems like one mistake could do major damage. I’d hate to pay a lot when I can get a new filter for $30, but I’d hate even more to screw something up and pay even more. Is there anything special I should do, or should I just take it to the guys I trust and get them to do it next time I get my oil changed?

Turn the ignition OFF. No problem. No pressure in fuel system until engine is fired up.

That simple, huh? Then why does the manual warn me in big scary terminology that it’s dangerous and I should only have it done by my Subaru dealer?

Oh, wait…

On my Ford Ranger, there is a inertia switch that kills power to the fuel pump in the event of an accident. Changing the fuel filter involves disconnecting this switch with the engine running to turn off the pump. The engine will eventually stall as fuel pressure drops, at which point it’s supposed to be ok to change the fuel filter. EXCEPT that fuel still sprayed all over the place when I removed the old filter. Next time I do it, I’ll bleed off the excess fuel at the fuel pressure gage port on the fuel rail. Get a shop manual for the Subie and I bet it will detail how to change the filter. The owners manual will just tell you to go to a shop since they don’t want everyone playing around with gasoline.

Or, you can consult your manual and pull the fuse that controls your fuel pump, then crank/run the engine a little to get the fuel out of the lines. That should relieve the pressure.

NO, NO, NO. This is 100% incorrect
::: waves arms like the robot on Lost in Space:::
Danger Will Robinson, Danger, Danger.
Look the pump does not run with the key off, but the system holds a residual pressure that could be as high as 50 Lbs.

Because there is an excellent chance that it is not that easy.
Modern fuel filters may be held on with banjo bolts that requre an impact wrench to loosen or tighten, or they may require a special service tool to access. Many modern filters are now located inside the fuel tank and either require removing part of the interior to access or dropping the fuel tank to access. The access hatch on the tank, may require the use of a special wrench to loosen / tighten.
I’m not trying to tell you that you can’t do it, but I am trying to tell you it may not be the walk in the park some people are leading you to believe.
If Gary T stops by we might be able to get a better read on what it takes to change this filter.

Subaru fuel filters are among the easiest to change because they’re located right where you can get to them in the engine compartment. This is as opposed to under the car for most American cars or in the engine compartment but well obscured for many Asian cars.

All of the official instructions for fuel filter replacement on modern cars make a big deal of relieving system pressure (which as Rick correctly points out is maintained even with the ignition off) before replacing the filter. Why? Because otherwise fuel will spray out when the pipes/hoses are disconnected from the filter, and this is a potential fire hazard.

Real world? BFD. The actual chances of having a fire (using reasonable precautions) are about one in a million. I do not relieve pressure before changing fuel filters. Of course, I’m not going to offically recommend that, and neither are the car manufacturers because they don’t want to get sued by some schlub who manages to start a fire.

Whether you relieve pressure or not, there is going to be some fuel dripping out of the pipes/hoses and filter. I prepare for the fuel spillage, and wipe it up before starting the engine.

Make that one in a half a million. I know of a case where a technician (who should have known better) took the banjo bolt off with a cordless electric impact. Fuel sprayed and caught fire from the electrical arc inside the wrench. :eek:

Ouch. He missed the “reasonable precautions” part. That includes making sure there are no ignition sources nearby.

I would never use an impact on a banjo bolt. For one thing, it’s not necessary - regular wrenches can do the job. Some of those bolts are godawful tight, but with enough leverage they will break loose. For another thing, to avoid twisting of the lines one must use a backup wrench on the filter body (which has a hex on it just for that purpose). Holding a backup wrench on a mounted-in-rubber filter against an impact is pretty tough to do. Sorry he had a fire, but I shake my head at his method.

Similar to Dag Otto’s post, the folks at Saabnet told me to remove the fuel pump fuse, start the engine, and let it run until it starves.

Worked well on my Saab, dunno about Subarus. I expect that there is a Suburu forum out there where you can get some good DIY advice.

Ditto that. I changed the fuel filter on my old car ('99 Legacy GT) without difficulty, other than the time it took to figure out where the damn thing was at (driver’s side aft area of the engine compartment, way different from my '83 DL-10 wagon). Letting it sit overnight seemed to reduce the pressure; I got a little bit of spray but nothing scary and dangerous. Subaru’s are mostly a joy to work on, even moreso than most Japanese cars. Compare to changing the fuel filter on, say, a Chevy Corsica: Step 1: Drive off cliff. Step 2: Sigh of relief. Step 3: Purchase new car.


Yes, there’s a lot out there on the internet. I just came here first to get the general idea before I started really searching.

Don’t be complacent about “a little bit of spray.”

I had a rag over the filter and a couple more covering the nearby components in the engine bay and protecting the fender; the rags then went into the bleach-water bucket for a good soaking. Generally speaking, it’s best (and on some cars, absolutely necessary) to bleed down the system, but not a big deal on the Subaru.


Sure brought out a lot of considerations to observe for pressurized fuel systems in general.
My hat’s off to all of you. :slight_smile: