Do You Smell Gas?
By John McLelland
We've had reports from customers who have had the experience of opening their garage door and being assaulted by the strong smell of gasoline. Their first impulse was to check if gas was leaking from the vintage muscle car or street rod parked there.
The gasoline odor seemed strong enough to cause worry about a potential explosion. After opening the hood, checking the carburetor, fuel pump, fuel filter, rubber fuel lines, and then moving back to the gas tank, no leak sources could be found. The next step toward solving the problem involved disconnecting the line from the fuel pump to the carburetor. Again, no obvious leaks. Further examination revealed that the hose appeared to be letting fuel vapors pass right through its walls. The exterior of the hose felt moist and a finger rubbed along its length smelled strongly of gasoline. This phenomenon is called permeation, and its presence absolutely rules out the use of common rubber fuel lines in any modern hot rod application. Vapor permeation, as it is officially termed, happens because today's unleaded pump gas, with myriad additives, creates vapors that can eventually pass right through the walls of rubber fuel hose. Permeation could involve older vintage street rods, muscle cars, and trucks where standard fuel hose or high performance stainless braided rubber hose was installed originally when pump gas was not as unfriendly to rubber as it is today. Many of these hoses have now been on the cars for several years and could cause some severe permeation issues. Most modern, unleaded fuels are blended with 10% ethanol along with countless additives and harsh detergents to keep fuel injectors clean and emission levels down.
There are at least 23 different blends of gasoline being sold in the United States so it's impossible to know what fuel is coming out the pump at any given time, or how it's affecting the fuel hose. One thing is for sure, the pump gas of today is harmful to the old nitrile rubber fuel (SAE30R7) hose, originally rated for low-pressure (up to 50 PSI) and used on every passenger car and truck into the '80's. Even many high performance braided stainless reinforced hoses use nitrile and are subject to the same deterioration and permeation rate (passing 30 times more hydro-carbons than SAE30R9fuel injection hose).This is especially true when the fuel stagnates in the hose for a long period of time (like it does in seldom driven street rods or muscle cars). Availability of replacements for old stock factory nitrile rubber hose is limited. The only hose replacement found is the fuel injection (SAE30R9)hose, readily available, and suitable replacement hose at a modest cost. These hoses retain the "stock factory look", but are chemically engineered for modern unleaded pump gas, and E85fuels. Be careful of lower cost, so-called budget brands. Hoses manufactured "across the pond" can look the same as USA made stainless steel branded hose, but with no Society of Automotive Engineers (SAE)in place to monitor standards, the stainless steel braid may not be bonded or extruded correctly through the rubber, the hose bore may not be concentric or of even thickness which will eventually result in vapor permeation, not to mention ballooning and leakage or failure, especially at the fittings. These days it's difficult to tell just where any aftermarket hoses are really manufactured. There are numerous private label brands on the market. Carefully research each hose product before making any purchases. Most companies have recommended I.D. and 0.0 hose specifications and these are important when purchasing the correct hose ends. Spending less now, might hurt your pocket book later.
Almost all of the manufacturers we contacted are either making permeation proof hose or working on development of same. All highly recommended the use of Teflon" (PTFE) hose to be sure of eliminating the permeation problem. Although not as flexible as rubber hose, Teflon" hose definitely keeps vapors contained. (NOTE: aluminum hard line can also be used in place of rubber or braided hose.)
Keep in mind that once any hose has been installed, preventative maintenance is the key to long term elimination of the vapor problem. Also, it might be wise, if storing a car for long periods of time, to purge the fuel system completely.
*Teflon is a registered trademark of Dupont