Many classic cars of the bygone era of the ’60s & ’70s, not just Mustangs were fitted with a fuel filler pipe that was quite big diameter. The fuel back then was Leaded or Four Star fuels to be pumped through a larger nozzle which filled more of the filler pipe, which makes perfect sense. When pumping was complete, the pump would click off and it was job done. However, with the move to the dreaded ethanol based fuels the filler pipe holes were made smaller along with the pump heads themselves. Fuel pumps from today have the much smaller hole which ensure a snug fit and allow the pump to shut off as you would expect. The problem with classic cars owners now have since this change is that the the large diameter filler pipes still take the smaller pumps which fill at similar rates, but at higher pressure. In turn that when the filling is complete, the fuel should stop the nozzle to avoid over filling, but it more often than not doesn’t. The reason is that pumped gas under pressure can splash back around the smaller nozzles, down sides of the filler pipes and out the top. This invariably results with some splash back out of the filler pipe over the paint job, bumper and if I’m unlucky, me if I happened to be standing in the wrong place. With this in mind I tend to go through some performance of getting a microfibre cloth, laying it over the bumper ready to clean up quickly when I top the tank up. I sometimes get strange looks as to what I’m doing before filling up.

This waste of fuel, smell on your clothes and potential damage to the paint work over time has always been an annoyance to me, but it’s part of the ‘joys’ of owning a classic car. I know many other Mustang owners as well as other manufacturers in fact that suffer from this issue. I just happened to be browsing through a Mustang forum where I spotted a link where somebody had modified the 64 – 70 Mustang filler pipes, a totally random link lead me to a discussion. The filler pipe size was exactly the same as the original, but inside is a simple fitted anti splashback valve. The valve is designed for the unleaded fuel pump nozzles sizes of today 13/16″ and should stop the splashback problem.

After a bit more research I got in touch with the guy and ordered one. A couple of weeks later it arrived and got round to fitting it as the sun came out over the weekend. Below shows the inside of the filler pipe with the anti splash back valve.

I have created a full step by step fitting guide for the filler neck here, but I have shown the basics steps of fitting it below.

This is an exact replacement for the standard filler pipe. The only minor difference is the bottom of the filler pipe has a slightly ribbed bottom which should aid in sealing of the hose to the pipe.

The only difference as i mentioned is the internal fuel valve. The definition of fuel ‘valve’ is a piece of sprung metal behind the reduced filler neck size opening. There are a couple of breather holes as well, two at the top and one where the bottom of the flap finishes almost at the bottom of the filler opening. The inner valve is held in place with a few dimples and a bit of JB Weld.

Roll the trunk mat out of the way to expose the top of the fuel tank. I have a a sound deadening mat on top of my polished tank which is semi stuck down. Remove the fuel cap, if you have the security version like mine there is a threaded bolt that goes through the filler panel and held in place by a nylon nut. Undo the nut and remove the security wire and the cap.

There will be four bolts around the outside of the flange which will need to be removed.

Inside the trunk there is a rubber hose clamped in place by two wire fittings. It’s easier to undo both the top and bottom clamps. Either the fuel pipe needs to come out of the rubber hose. Or pull the rubber hose up of the neck of the fuel tank itself. Either way is fine, you just need to remove the pipe from the hose.

In my case the hose came off the tank first. With the fuel pipe now free, remove the hose from the pipe otherwise the filler will not go through the panel as the opening is fairly snug.

Fully remove the pipe along with the cork gasket from the rear panel. Be careful not to let anything full into the open top of the fuel tank, I placed my fuel cap over the opening to prevent anything falling in it.

With the pipe removed I cleaned and applied a long lasting wax to the paint before i added the cork gaskets back on. You only need one gasket, but I like two, as it helps with the alignment of the filler pipe and also gives a little more protection of metal filler pipe flange to the paint.

Add the gasket(s) on the pipe before before feeding the pipe through the rear panel.

With the pipe through the panel it’s easier to fit the hose to the pipe by turning it ninety degrees. Then turn the pipe back round to the correct position and then you can simply press down the hose to the fuel tank opening neck.

With the hose now in place we can add the screws to hold the pipe’s flange to the panel. I started by adding the anti theft bolt through the gaskets and the panel. Add the washer to the front side of the flange, then the second washer inside and finally the nylon lock nut on the inside. Don’t tighten anything up just yet.

Next arrange the clamps how they should be on the rubber hose. When I first fitted the filler pipe and the hose I had the clamps on the inside of the trunk, this mean that things like cloths would catch the bolts. See below right hand photo. I never changed their position until now. The clamps should be between filler pipe and the rear panel so they are out of the way. Left and middle photos below. Lightly tighten the clamps just to hold them in place for now.

Align the gasket(s) up to the holes and add the rest of the screws to the flange and gently tighten up to allow for final adjustments.

With the screws in place start to tighten them up and the bolt for the security wire. Ensure the security wire is aligned with the outer part of the flange, or you won’t be able to fit the cap back back on. Tightening of the bolts or screws will pull the pipe into position on the panel. Now go back to the hose clamps and fully tighten them both up as the rubber will take the difference of alignment up. Recheck all bolts are tight.

The filler pipe was a like for like swap, but now I have little more bling under the trunk with the nickel plating looking great.

From the outside there is no difference to see. But, on the inside there is something (in theory) to stop me getting my regular splashback on fill up. Once I have taken the car for the next fill up I will give the results if the splashback is cured with this little project. It can’t be any worse no matter what happens.

I’m now intrigued to know if any other classic car owners have the same problem, or have hacks that they can share with us.