Adapting Fram G3727 or Dura FF3504DL Fuel Filter to any Lines

The famous Fram G3727 fuel filter is threaded at both ends with female 16 mm x 1.5 pitch, ideally for an O-ring fitting.

They are ubiquitous and useful: Fram G3727, Autozone FF3504DL, WIX 33481, NAPA 2481 fuel filter. Threaded with female metric 16 mm x 1.5 thread at both ends, they’re designed to take O-ring fittings, or can be hacked to work with various other available pieces and parts.

Here are a couple of alternative ways to hook these filters into your resto Corvette, engine swap Jeep, or whatever.

At first glance, I had trouble figuring out how to adapt my modified Jeep fuel system to the G3727. Internet research and hands-on experimentation revealed the following.

1. If you want nice clean -AN fittings on your rig, get yourself a couple of 2 Earl’s 991955 Aluminum -6AN Male to 16mm by 1.5 Power Steering/Fuel-Injection Adapter Fittings.

2. If you’re in a hurry and going to NPT fittings, it just so happens a 3/8 inch flare male (5/8 18 threads) threads into the female filter sockets. Throw a brass washer in there and tighten firm, install with plenty of J-B Weld for insurance (though take care you don’t contaminate gasoline with fragments of hardened J-B on the fuel pump side of the filter. This type of fitting could be used to adapt to NPT threads, or perhaps with flared tubing. While tightening fittings, be aware that the filter housing is thin soft steel so grip the fixed nut with a wrench for counter-force rather than holding the fitting.

3. You can adapt 3/8 NPT male NPT threads (for example, on a connector or adapter that takes you from 3/8 NPT male to 1/8 NPT female) by cutting with a 16 mm x 1.5 die, then install with J-B Weld and a brass washer. Rig up the fitting on a spindle you can chuck into an electric drill, then rotate as you reduce diameter slightly with a disk grinder, allowing you to get the die started. You can do this with either a brass or aluminum fitting. For example, a Russell part # 660460 -6AN x 3/8 NPT can easily be tapped down to 16 mm thread.

Prepping 3/8 NPT threads for threading to 16 mm requires a moderate reduction in diameter. Do so by making a holder for your drill, then spinning the fitting while you touch with a disk grinder.

If you used J-B Weld, remove fittings by heating with a heat gun (for safety dry fuel out of filter by blowing compressed air through it, doesn’t take long).

In my opinion it’s best to use long-cure regular J-B for fuel applications, and cure overnight before wet testing. That said, when in a hurry I’ve used J-B Kwik with continued success.

I’ve tested these mods quite extensively, but only on a low pressure carbureted fuel system (around 5 PSI). My understanding is that Option 1 above, using power steering fittings, is good for higher pressure fuel injection systems. Nonetheless I’d test with fuel injection pressures before trusting.

A few more tips: If you care to grab G3727 compatible fittings from a salvage yard, look for something along the lines of a 2005 Chevy Astro Van and many other gasoline fuel injected GM automobiles. Know that the steel body of these filters is thin and weak. While installing, don’t try to bend lines by shifting the filter body, you’ll only bend the steel at the ends of the filter. Always use two wrenches while tightening fittings, don’t depend on hand-holding the filter as you tighten.

Fram with Autozone equivalent.

With 3/8 flare fitting snugged down firm on brass washer. I tested without J-B Weld and had no problems, but added some for insurance. Probably best for carbureted applications with gravity feed or fuel pressure around 5 PSI.

Brass washer and J-B Weld should be used with anything but the O-ring fittings mentioned above.

All the parts used when I did not have an 0-ring fitting, flare and brass washer.

Filter with Earls 991955 Aluminum -6AN Male to 16mm by 1.5 Power Steering/Fuel-Injection Adapter Fitting.

Hardline fitup between filter and fuel pump using the 3/8 flare and a step-down to 1/8 NPT. Yes, the odd angle of the mount is done to utilize the filter as a sump for steep climbs and angles that sometimes slosh fuel away from my tank outlet.

Fram with Earls AN fitting on one end, 3/8 brass flare on the other that adapts down to 1/8 inch NPT. The Earls fitting is installed with tef-tape so it thread locks better without over-tightening. It appears from measuring the O-ring and corresponding land in the filter that the O-ring could easily be over compressed.