Change often comes with compromise, and that is certainly the case when it comes to today's gasoline. It's not the sweet-smelling, pseudo-solvent fuel we all grew up with--well, most of us anyway.
Modern gasoline is an aggressive-smelling chemical with plenty of additives. It burns cleaner, which is great for performance and emissions, but its composition permeates rubber, including fuel hoses. In fact, it can actually seep through rubber hose, drying it out prematurely and causing it to crack, weep, and possibly even fail.
This is an increasingly common problem these days and one you may have noticed, as it manifests itself as the smell of leaking gas. Typically, the smell is caused by the fuel "boiling" through the rubber hose as the vehicle sits in a garage. Beyond the safety issues of having gasoline vapors in your garage, this eye-watering odor is an early warning sign that a rubber fuel hose is on its way out.
While you can't change the gasoline that feeds your engine, you can make a change to the hoses that carry it, eliminating the problem--and smell--altogether. The solution is swapping out the conventional rubber fuel hoses with PTFE-core replacements. PTFE is the abbreviation for PolyTetraFluoroEthylene, but you know it more by its common trade name, Teflon.
PTFE hoses have been around for a long time, used mostly for brake- and hydraulic-fluid transfer applications. The big advancement in PTFE fuel hoses is that they now are available with a "conductive core" inside. This a carbon lining added during manufacturing that, when combined with the fittings that install on each end of a hose assembly, provides a path for any static charge in the line.
If you're wondering where a static charge would come from in the fuel line, it's a quirk of the PTFE material. When a non-conductive fluid, such as gasoline, diesel, ethanol, methanol, or a similar product passes through it at high velocities, stray electrons--in the form of static electricity--are generated. That's obviously a condition you don't want with gasoline, so the conductive core of the PTFE fuel hose eliminates the chance that the static charge will find a ground and flame-broil your Vette like a Labor Day barbeque.
Conductive-core PTFE lines are a specialty of Michigan-based TechAFX. The company agreed to guide us through a tutorial on the subject and even demonstrate the process of building new AN-type fuel lines/fittings for a Corvette. TechAFX is a leading developer of aftermarket PTFE components, with products built not only to OE vehicle engineering standards, but military specifications.
As you might imagine, PTFE hoses are more expensive than conventional rubber fuel hoses, but not prohibitively so. It's definitely an affordable upgrade--and one you should only need to perform once in the life of your car. By comparison, rubber hoses may require more than one replacement to keep the odor of leaking gas at bay.
The accompanying photos illustrate the basic steps in building PTFE hoses and fittings for use on a Corvette, but there are few tips and tricks to keep in mind:
To prevent the Corvette flambé situation described previously, it's imperative that only conductive-core PTFE hose be used for fuel lines. These are easy to spot, however, because the inside diameter of the hose is black.
PTFE hose is too stiff for hose clamps. It won't "crush" onto a fitting to create a good seal, so unique aluminum AN fittings (developed by TechAFX) must be used to secure it.
PTFE is stiffer than rubber hose material, even though it has a much smaller outside diameter (about one-third the size, to be precise). That means the new hose can easily match the bend requirements of most applications.
Cutting PTFE hose is no different than cutting rubber hose, but AN fittings use a brass ferrule, or "olive," that crushes to provide the seal at the fitting/hose mating point. Because most PTFE AN fittings are a non-swivel type, it's difficult to create complete hose assemblies. Fortunately TechAFX has a semi-swivel fitting that can be rotated on the hose to make it easier to build an assembly at home.
Although there are a few very-expensive, crimp-fitting PTFE AN hose/fitting products on the market, TechAFX is the only supplier we've found with aluminum fittings designed to work with the more common -6, -8, and -10-diameter hoses for do-it-yourself projects.
A couple of other notes: TechAFX stainless-steel-wrapped, conductive-core, PTFE hose is called BlackWrap, which is what is shown in the our photos. This hose features a black rubber coating that looks great, minimizes abrasion issues, and aids in hose assembly. And like the basic PTFE hoses, it's offered in -6, -8, and -10 sizes.
Also, one of the longstanding problems with PTFE fittings and hose has been non-swivel designs, which made "clocking" the fittings very difficult. Our project features a semi-swivel AN-fitting design that pretty much solves the problem, but some trial-and-error test-fitting is still required.
We found the job to be very straightforward and easy. And after building the hoses, it was simply a matter of swapping them for the lines on the car. Keep in mind, however, that this project requires you to carefully relieve the pressure in the fuel system. It's best to let your car sit overnight before attempting it--and even then, wear eye protection and make sure the area is clear of any source that might ignite spilled fuel.
Your hands will smell like gas for the rest of the day, but after that, your Corvette won't.
Why Gasoline?
Gasoline has been the automotive fuel of choice for about a century because of one thing: energy density. It delivers more bang for the buck than any other competing material.
In the early days of the automobile, all types of petroleum- and alcohol-based fuels were used. It was a brave new world, and there were no standards. Henry Ford liked ethanol because of its agrarian source, but alcohol-based fuels corroded aluminum, rubber, and other engine and fuel-system parts. Sure, alcohol burned cleaner than petroleum, but back then, nobody cared about emissions.
Besides offering beneficial engine-lubricating properties, petroleum-based fuels' greater energy density meant drivers could go farther on a tank than they could with the same amount of alcohol-based fuel. Gasoline was also a light petroleum product that was easy to ignite in the engine using a spark plug. The other petroleum fuels, including diesel, were heavier, harder to ignite, and much dirtier when burned.
Diesel actually has greater energy density than gasoline, but until recently it was a non-starter with American motorists because of its dirty, sooty emissions and a few terrible examples of diesel-based production cars. Cleaner diesel fuel and more-elaborate emissions systems are helping change opinions, but gallon for gallon, diesel still produces more emissions than gas. On the flipside, that gallon of diesel takes you about 20 percent farther. A gallon of gas, meanwhile, takes you about 20 percent farther than a gallon of cleaner-burning ethanol-based E85.
So, it was gasoline's balance of energy density and relatively clean-burning properties that made it the fuel of choice in the early days of automobiles. The crude oil from which it was made was an afterthought, too, because the United States produced every drop it needed. Oil imports didn't start in earnest until the 1960s, and even then, they represented a comparatively small percentage of the oil used in America. As late as 1973, the U.S. imported only about 35 percent of its oil. Today, it's more like 75 percent.
The political and environmental issues that have grown up around the gasoline pump have more people than ever questioning its viability. But the detracting features of the other fuels haven't really changed in the past 100 years. Gasoline may not be perfect, but it will likely remain the fuel of choice for the foreseeable future.
1 Here’s a closeup of TechAFX’s...
1 Here’s a closeup of TechAFX’s BlackWrap PTFE AN hose and black-anodized aluminum fitting. While installing a fitting on the BlackWrap is a little different than doing so on an old-style rubber AN hose, it can still be performed pretty easily in your garage. You’ll need a sturdy vice.
2 All TechAFX PTFE fuel hose...
2 All TechAFX PTFE fuel hose is “conductive core,” which means it has carbon black added to the inside diameter to conduct static electricity away from the fuel passing through it. The fittings use a brass “olive” to seal the hose to the fitting.
3 Cutting the PTFE hose can...
3 Cutting the PTFE hose can be accomplished with the same tools employed on traditional stainless-steel-wrapped AN hose, such as a chop saw (used here), handheld cut-off wheel, hacksaw, and so on. This project started with a measurement of the desired length before cutting. Hold the “cut” end while sawing to ensure a straight cut.
4 After the hose has been...
4 After the hose has been cut, it should be cleaned out with solvent and pressurized air to remove debris. The importance of this step can’t be overstated, for obvious reasons.
5 The next step is to remove...
5 The next step is to remove 7⁄16-inch of the black sheathing to install the fitting on the end of the hose. By the way, the BlackWrap hose looks absolutely great under the hood, but without the high cost and complexity of black PTFE hose. Very cool.
6 A utility knife is used...
6 A utility knife is used to cut around the circumference of the hose. After that, a slit is made in the section to the end of the hose.
7 The BlackWrap coating is...
7 The BlackWrap coating is then peeled off to reveal the stainless steel underneath.
8 Next, the collar for the...
8 Next, the collar for the fitting is pushed on from the other end of the hose (a neat trick that makes the install very easy), in preparation for assembling the fitting.
9 Using a small, flat screwdriver,...
9 Using a small, flat screwdriver, the outer stainless-steel braid is peeled back from the PTFE core. Note the black color on the inside diameter. That’s the giveaway that it’s the crucial conductive part of the hose.
10 The brass “olive” is then...
10 The brass “olive” is then pushed between the braided steel and the PTFE core.
11 To fully seat the olive,...
11 To fully seat the olive, TechAFX recommends pushing the hose/olive assembly into the bench top (or something similarly firm) until the hose core bottoms out.
12 TechAFX offers these aluminum...
12 TechAFX offers these aluminum awls to push the PTFE core into the walls of the olive. Failure to do this might result in the PTFE core getting folded over when the male end of the fitting is pushed into the hose/olive assembly.
13 The hose/olive combination...
13 The hose/olive combination should look like this when you push the male end of the fitting into it. TechAFX suggests wetting the male end of the fitting with some water before installing it; this provides lubrication that makes the task easier.
14 The male end should seat...
14 The male end should seat fully into the PTFE hose/olive combination as shown. And, as also demonstrated here, an inexpensive set of aluminum vise jaws makes this job much easier.
15 The fitting must be relocated...
15 The fitting must be relocated into the aluminum vise jaws so that the collar can be pushed up to the fitting; the threads between the collar and base of the fitting can then be started by hand.
16 A high-quality wrench...
16 A high-quality wrench should be used to tighten the collar onto the fitting. The collar should be torqued to 37 lb-ft (slightly past hand tight), but not until after the other hose fitting has been attached and the assembly test-fitted on the vehicle. This way, the TechAFX “semi swivel” feature (see main text) will allow precise “clocking” of the fittings before final torquing. And that’s it. The project is complete.