Boys and Girls,

I recently picked up a spare fuel filter from Advanced Auto and noticed it was too big. This is the stock filter arrangement (351W 2bbl) that threads into the front of the carb, with a rigid line attached. The rigid line makes an S-turn to clear the distributor so it's very tight in this area.

This picture shows the suspect Advance Auto (CarQuest) #86081 on the right. For comparison, a NAPA 3081 is shown on the left. Note how the correct filter is about 1/4" shorter:




I double checked #86081 is "correct" per the Advance Auto website. They also show another number #86933 that looks similarly too big:

https://shop.advanceautoparts.com/c4...upId=-49998334


Normally I recommend Advance Auto as a good source for parts (along with NAPA) but this one is a little bit off. Just a little something to keep in mind when replacing your fuel filter.

 

That is a good catch on the filter differences.

Were it mine, I would gut the filter that screws into the carburetor so that it is nothing more than a decoration on the fuel line; then, I would go somewhere ahead of it and add a much easier to service filter, rerouting lines to a better location if I had to.

When you do so, be sure to choose a filter that is common as hair on a dog's back and therefore readily available anywhere and inexpensive as well.

 

Oh, the stock location is fine. There's just not a surplus of room, that's all. In a pinch I could have made the longer filter work, but the original compact size is preferable.

 

Bumpity bump. Found another potential problem with this type of filter.

The female end of the filter is a reverse flare design, similar to s brake line. Inside the recess is a cone that mates to the flared end of the metal supply line. The threads here only provide the force to clamp the flared tube against the cone.

I discovered the cone's dimensions slightly different on some brands. The cone is slightly shorter. You can apply an ungodly amount of torque and yet the flare never properly seats against the cone.

I've installed different brands of fuel filters for years with no problems. Something must have changed in production as lately I've had several leak. This is at both locations on my truck (I have an extra filter before the electric pump, as recommended by the manufacturer) and on my Jeep. I don't think I've got a damaged flare as all three locations have been problematic recently.

The only brands that didn't leak for me:

Motorcraft
NAPA

Strikes me as odd the NAPA filters have been fine, as I believe they are made by WIX, which has given me lots of trouble.


Leakers:

WIX
Microguard (store brand of an unspecified chain that rhymes with No'Reillys)
Purolator


Haven't tried recently:
Fram
AC Delco

I'm curious if anyone has encountered the same problem recently, and which brands did and did not work

 

So I gets to thinking. I rigged up a test, with a piece of flared 5/16 line and flare nut. This is one of those preformed lines you find at any parts store. I put an 1/8” NPT cap on the other side of the filter, where it threads into the carb.

I pressurized the filter and attached line to about 15 PSI and submerged it in a bucket of water. Sure enough, the WIX and Purolator filters bubbled like crazy at the flared connection. The Motorcraft and NAPA filters sealed perfectly.

I was able to test 4 different filters with the same preformed test line. I wanted to rule out any possible variations with the existing lines on my truck and Jeep. Sure enough, two brands leaked and the other two were fine.

Kinda sad that new parts can be so bad right out of the box.

 

There's Your Problem ...

And you buy by quality, not price.

It is OK to price shop.

Another heart breaking factoid. Cellulose filter media breaks down with ethanol laced gasoline.

 

Tested another brand, a Baldwin BF920.

This one failed the leak test, too. The body was also too long, as noted with some other brands in an earlier post.

 

Are you referring to the country of origin? I’ve found it doesn’t seem to matter with these Leak-O-Matic filters.

With other products, I’ve noticed Taiwan stuff is usually pretty decent. Wasn’t that way 30+ years ago, but they have improved dramatically since then. Nowadays, China has one of the worst reputations. But the only brands that have passed my test are Motorcraft and NAPA, both from China. Go figure…

 

That's surprising that the Wix filter leaked.

 

I wonder if the threads are compatible? Do they seal to a gasket or are they NPT threads? Some other variant? Threads and fittings have to be meant for each other. You know like you and the second wife? I recall you mentioned things didn't go well on the first one...you just didn't mate up.

 

I had the same issue with the flair nut fitting on my new fuel pump.You really need to crank it on to seal. Almost like the seating cone is the wrong shape.

 

The output side of the filter has 1/8" NPT threads, where it threads into the carb housing. These are tapered threads that wedge tighter the further you turn. Just a smidge of Teflon paste and these seal perfectly, no problems there. This is the same as old school household plumbing with iron pipes and threaded connections, only smaller.

The input side of the filter has a flared connection, where the metal fuel line attaches. The style is like a brake line with a B nut, only a little bigger. The threads are straight and free running. The threads do not do any of the sealing. The threads only provide the clamping force to squeeze the flared end of the metal line against the matching cone inside the end of the filter.

The problem seems to be the dimensions of the cone is not consistent from brand to brand. Using the same prefabricated test line (commercially made, not homemade), the good brands sealed perfectly with minimal torque. The leakers never sealed, no matter how hard I reefed on the fitting. For the test, I ate my Wheaties but still no joy. Just to make sure the metal line did not get damaged during testing, I went back to the good brand and the same line sealed again no problem.

I suppose maybe the threads of the leaky filters weren't formed all the way to the bottom. That would let you apply full torque without properly squeezing the metal line against the cone. But even if that were the case, the leaky brands were not properly machined as the same test line sealed perfectly with other brands.




For that analogy to be accurate, the first filter would have had to run off with another fuel line, clean out the bank accounts, and take the house.

 

Maybe the answer to leaks lies here?

https://titanfluid.com/npt-vs-nptf/