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How to diagnose a fuel filter

Hello all. How do you know when it’s time to change your fuel filter?

By the service schedule. It will advise based on miles/time when to change each filter.

Some cars do not have any specified period like my old 95 Honda Civic. I changed it for the first time at 190k miles/6 years.

Do you know that it didn’t have a schedule for the fuel filter, or is it that none was listed in the owner’s manual? Sometimes the factory service manual is needed. 190K seems too long, I wouldn’t go more than 50K. There are two possible outcomes with old filters. First, is that they may clog and cause running problems, or stop the car completely. The second is that dirt may start going past the filter and cause problems with the injectors.

My owners manual for my 98 pathfinder says to change it every 60k miles. I change it about every 30 and it’s FILTHY every time I change it.

Fuel filters should be changed every 25-30k miles and even more often if fuel contamination is even suspected.
The problem with allowing a filter to remain in place for eons is that a filter can partially clog, the vehicle will run fine, but the clogged filter is causing the pump to work harder.

This means a shorter pump life and increased electrical current draw by the pump; and that in turn means fuel pump, main relays, or even ignition switches may be more prone to failing.
VW had problems with fuse blocks and wiring failures due to dragging fuel pumps and this is JMHO here, but many of Honda’s main relay problems are likely caused by the same thing.
Dirty fuel filter drags down fuel pump which drags down electrical items all through the chain.

If you change the filter drain the old filter and allow it to sit for a few hours to dry out. After a couple of hours try to blow through the inlet side of the filter.
You should be able to EASILY blow through it if the filter is good. If you feel a slight restriction, any at all, the filter is partially clogged. Compare it to the new filter; you’ll see what I mean.

You look in the owner’s manual. It tells you how often to change that and lots more maintenance stuff. You should never leave home with it.

Just an FYI as to how quick a filter can go bad, I don’t remember exactly how many very low miles vehicles I’ve seen towed in because of fuel filter problems but here’s a few examples.

Right off the top of my head I do remember a salesman’s demonstrator that had a shade over 400 miles on it when a bad load of gas caused it to quit. Another one (less than 1500 miles on the car) belonged to a doctor and it quit him while on vacation the week after he took delivery of it. (fuel filter-bad gas)
Another one left the owner stranded in the OK Panhandle on the weekend. (also fuel filter - 4k miles on the car)

Mileage is irrelevant. Much depends on the gas station filtering system, the amount of sediment involved, and some plain old luck.

If it’s to the point that you’re even bringing it up…change it. Certainly won’t hurt, great regular mintainence, & avoid the big repair bills that come along if you don’t. ( I change mine once a year without wondering or waiting for symtoms. )