I believe that, unless the filter is seriously clogged, the actual "botlleneck" which determines the load on the pump is the pressure regulator, except maybe at very high RPM.

 

Agreed! The bottleneck is the regulator, but it's important that the bottleneck is downstream of the injectors. A 50% clog in the fuel filter (speculation alert) may not allow the injectors to have full flow, since it may take some time to build back up to regulator pressure through a restrictive filter, leading to a potential lean burn condition. The down side of a clogged fuel filter, to me, does not warrant letting it go for over 100k without changing, especially since it is such a small filter.

 

Subaru recommends changing it every 30k for cold or severe duty and 120k for normal service, so maybe I'm a bit anal, but I've gotten dirty gas before and clogging up a filter is not fun. Conversely, Saab recommended 30k intervals and that car had a filter that was about 6 inches long and about 4 inches in diameter. That's a huge increase of the Subie filter size, probably well over four times the volume.

 

Again, for a $15 part that takes 5 minutes to change, why risk stressing a fuel pump or the associated potential for a lean condition in your engine?

 

Jack

My reply was about what restricts the flow in the system. Replacing the filter is still a good practice.

Nope, I agree with you, but i'd rather replace a $15 part every 50k or so than take the time and effort to monitor the fuel pressures up and down stream of the filter.

 

OTOH - in my home I have a magnehelic differential pressure gage across the furnace filter so I know when to replace the $20 filter element.

 

Jack

 

The double gauge project is just an experiment. I would'nt propose this as normal practice. I like mechanical work. I like to take good care of my car and save some money in the process. I also like to learn about things and am ready to do some experiments.

Everybody seems to agree that it's not a good thing to keep a dirty filter, but there are differences of opinions on how long it takes to make a filter dirty enough so it causes a restriction of the fuel flow to the injectors. I just would like to find an answer to this question.

Take care.