My brother and I have been working worth and restoring vehicles and combustion engines for over 35 years. We both have degrees and experience developing systems for air, sea and land vehicles in that time and have specialized in restoring vintage vehicles that are still in light through to heavy use today. In that tasks we use newer technology hoses, gasket materials and clips / fasteners - I've copied this treatise from the Volksbolts website hosted by Alan:
Technical Terminology UK / US
Petrol = Gasoline
4star = traditional British petrol rating = "premium" in the US
Aluminium - Aluminum
Fuel Composition Changes Over Time
Petrol has changed over the years : We remember filling up with BS4040 Leaded Four-Star.? (4* = Approx 98 RON) We now have 95 RON (3* equivalent) un-Leaded with there being some 97/98 RON (4Star equivalent) 'Super' Petrols.
The majority of modern (year 2015 onwards) Petrols are blends of classical oil Industry derived Petrols and Bio-Ethanols. In the U.K. up to 5% Of Petrol is Bio-Ethanol - As mandated by environmental Laws. This is referred to as "E5" blend (Typically 95RON).In the United States the content is up to 10% Bio-Ethanol in places (E10 blend) with Laws now being in place to permit the use of 15% Bio-Ethanol (E15 Blend).E85 and E100 are available in some places Globally.
As Of Sept 2021 E5 in the UK is being phased out and replaced by E10 blend fuel (10% Ethanol).
There are other additives in modern Petrols such as Oxygenators to promote cleaner burning; MTBE (Methyl-Tertiary-Butyl-Ether) being a well known additive in the USA.
Ethanol free Petrol (Zero Ethanol "E0") can still be found in the U.K. if you know where to look for it : These are exclusively Premium grades of 98/99 RON. 100LL "AvGas" is Ethanol free but at risk of discontinuance.
Why Use Ethanol?
The molecular structure of Ethanol allows the fuel to burn more completely and therefore give cleaner emissions; So its use in fuel has benefits for air quality. NOx, CO, HC and particulates are reduced by up to 30% which is great for reducing SMOG.
Tail-pipe emissions of CO2 decrease due to the lower Carbon-to-Hydrogen ratio of Ethanols : This makes Ethanol a great option for Governments to cut CO2 emissions nationally and hit Globally agreed targets.
Ethanol has a high Octane value (109 RON) but a low Energy value. This makes it compatible with classic Petrol but means you have to burn more fuel for the same output effect from an engine. You can increase compression ratio (CR) a little to help offset the loss in MPG due to the higher Octane rating of Ethanol. The ideal Air/Fuel ratio for old fashioned 4star Petrol is 15:1 (14.7:1 Stoichiometry) whilst with Bio-Ethanol it is 10:1 by weight - So some jetting adjustments may be needed to get the best results if you have Carburetors set up from the factory to run 4star.
Modern computer controlled Fuel Injection Systems will automatically adjust based on their own sensor readings. Older fuel injection systems such as Bosch K-Jet may require electronics hardware changes to cater for the use of E5 / E10 fuels. E5 has 5% Ethanol content and E10 has 10%. As the majority of cars on the road today are equipped with modern fuel injection computers and are generally designed with E5/ E10 in mind then Governments are happy to roll out E5 and E10 as there are no deleterious or unexpected side effects as such.
However, older (vintage / classic) cars designed and made in the "4star" era may encounter problems.
Problems with Ethanol
Unfortunately, these Ethanol & Oxygenator additions to Petrol are chemically aggressive and have a tendency to infiltrate and attack the Rubber compounds historically used to make fuel hosing, 'O' rings and accelerator pump diaphragms. These rubber components perish, swell and crack under the influence of Ethanol and ultimately fail in their function.
Weeping fuel lines can cause FIRES.!
There is a lot of anecdotal evidence on Internet Forums and increasing quantities of formal Technical Reports supporting this viewpoint; In both Automotive and Light Aviation user groups. A report from QinetiQ (The old Defence Evaluation & Research Agency, DERA) has been published highlighting these concerns in relation to Light Aviation where MoGas (ordinary Petrol Station Petrol) is used.
In terms of selecting an appropriate fuel hose for our classic cars we need to understand where the competing Standards of commercial fuel hose come from:
DIN - Deutsches Institut Fur Normung (German Institute For Standardisation)
Mil-Std - American Military Standards
FAR - Federal Aviation Regulations
As an Automotive specific standards body exists then we automatically have to make sure products conform to their standards for sale into the Automotive sector - this cover issues of liability. Though we could later cross-reference the other Standards to cross-sell into other fields such as Marine and General Aviation (MoGas Users). There is usually a high degree of overlap between Standards from these differing sectors as they do feed off each other somewhat.
The specific SAE Standard for fuel conveying hoses is SAE J30, which can be broken down into its individual sub-regulations as follows; The full SAE J30 specification can be downloaded by clicking here
The general evolution of the hose Standard can be seen; Higher numbers representing the latest generation of Standard. Though the gradings are not entirely linear; R12 is not necessarily better than an R10 grade as the two hose standards cover different application zones. The R6/7/8 Standards represent the drive to cut vapor emissions on carbureted cars in the 1980s & 1990s, with the R9 Standard building on this to cater for the introduction of fuel injection and bio-enhanced fuels.
It can be seen that R9 fuel hose that has been DESIGNED to work with modern fuels has less than 3% of the permittivity of 1980s & 1990s fuel hose. It even out performs the "A1" (ISO 7840) hosing mandated for use in the MARINE environment, where they are hugely stringent about fire-safety.! (See graph below)
The R6 & R12 data-points being from a reputable manufacturers data sheets; This shows that manufacturers try to EXCEED the Standard where possible.
The fuel injection grades of fuel hose (R9 & R12) are backward compatible with low-pressure carbureted cars. This and the exceptionally resistance to chemical attack, swelling and permeation of the R9 grade makes this grade ideal for use in the classic car sector.
The high permittivity of older fuel hoses means that as the bio-Ethanol content of Petrol rises that the older grades of fuel hosing will rot/perish/crack/weep at an increasingly quickening rate from the point of installation. This is because the escaping vapors 'wash out' the synthetic rubber compounds that help keep the fuel hose supple - the ensuing brittleness enables cracks to develop in the hose.
The Civil Aviation Authority (CAA) in the United Kingdom has issued a Mandatory Permit Directive (MPD) on Trelleborg "Hydro K" fuel hoses, mandating an elevated level of service checks on this type of fuel hose due to evidence of perishing in the above manner.
Is it worth putting your (expensive) vintage vehicle at risk of catching fire for the sake of some fuel hosing..? The SAE J30 R9 hosing is WELL WORTH the investment for the peace of mind it gives.
Fuel Hose Construction
Fuel hoses are usually constructed in layers rather than being single homogonous pieces of extruded rubber stock. This is because the inside of the fuel hose does a very different job to the outside; The inside being for the conveyance of liquid fuel and the outside being exposed to the air, heat and other chemicals found inside engine bays (oil and anti-freeze residues etc.)
The inside "fuel conveyance" layer of R9 fuel hose is FPM / FKM / Viton / Nitrile family rubber. A synthetic Fluoroelastomer rubber that has excellent chemical resistance with fuels and oils including Ethanol. The only material with better compatibility is PTFE / Teflon. However, PTFE is a lot more rigid and does not lend itself to being bent into radiuses in the same way that FKM / FPM rubber does.
A quick note here : "Teflon" and "Viton" are protected brand names held by DuPont of France and you are only allowed to use these brand names in sales and marketing material if you pay a license fee. This is reinforced by their lawyers whom scour online market places looking for infringements. Hence you will often see these materials marketed by their ISO / ASTM assigned chemical names FPM / FKM and PTFE. We use these words here for completeness of public information.
Fuel hoses will also have a middle layer that contains a reinforcement layer of fibers. These range from Cotton (in "Codan" brand hose) to Aramid (in "Cohline" brand hose). The reinforcement is sometimes encapsulated in a third rubber type.
This layering is visualized in the below graphic.
With the "Codan" R9 hose we see the construction goes (from inside out):
FKM = Fluoroelastomer for Ethanol tolerance
NBR = Nitrile Butyl Rubber to contain the Cotton reinforcement
CPE = Chlorinated Polyethylene Rubber for the engine bay environment.
CPE is used a lot to encase electrical wires as it has good heat and chemical resistance: so it makes sense to encase fuel hosing in this material.
With The "Cohline" DIN 73379 type 3E hose we see the construction goes (from inside out):
FKM = Fluoroelastomer for Ethanol tolerance
ECO = Epichlorohydrin Rubber
ECO = Epichlorohydrin Rubber
ECO is a more modern version of PVC / NBR that us used extensively to make waterproof roofing - good chemical resistance but can promote corrosion in metals so some caution is needed.
Fuel Hose Manufacturer Selection
In recent years concern over quality of R9 fuel hosing has been developing in user circles. There have been suggestions that R7 hose has been re-labelled as R9. Our experience with Codan is that fuel hose labelling can be washed so fresh labelling can be applied to custom order as they have done this for us. In our case it was removing a leading car manufactures labels and applying a standard "Codan SAE J30 R9" scheme of labelling in its place. Classic car owners also generally seem to be becoming wary of Chinese manufactured goods. A quick trip into Google will yield plenty of examples of this concern.
The independently researched and concluding advice on the V8Register Web-Site is To buy branded fuel hose from recognized manufacturers and AVOID unbranded "generic" hosing. The downloadable slideshows on this link are well worth a read through. The same sentiments are expressed on The Hot Rod Web Site where they observe "inferior Chinese hose and fittings have seriously "contaminated the supply chain" and where they suggest "buy name brand parts from a reputable manufacturer or distributor"
"Branded" fuel hose will have the makers name printed down its side-wall - in addition to the specification it conforms to and it's inner diameter. For example:
This makes perfect sense in-so-far that if you have made a great product then you would be more than willing to brand your name in to it. Reputable companies such as Gates, Goodrich, Codan, Goodyear etc., all brand their original goods. (This company list is not exhaustive)
Your chosen fuel hose supplier, shop or distributor should be able to provide a data sheet or a link to one on-line for your fuel hose, such as this one from Codan of Denmark - or this one from Goodyear
Fuel Hose Overlapping Standards
From 2014 onwards we have been aware of more "bio safe" fuel hoses, in addition to SAE J30 R9, being made available on the open market to classic car owners.
Gates "Barricade" being one such prominently talked about hose variety; though reputably difficult to find in the U.K and non-existent in the 5.6mm I.D size desired for air cooled Volkswagens. We have obtained a datasheet from Gates here
Looking at the datasheet we can see it is designed to meet SAE J30 R9 and R14 permittivity of 15gms/m²/day, Gates are reluctant to publish the exact material make up of "Barricade" hose so its construction may vary to that of competing products. (i.e. the inner liner may or may not be FKM. Or PTFE. The liner/outer configuration is followed as per normal fuel hose construction.
Interestingly the catalogue entry lists the Gates Barricade hosing as "Marine" but the datasheet does not explicitly state any conformance with ISO7840 Marine Hose Standards. The advice we have to give here is to only use hose clearly marked as compliant with ISO7840 if you are fitting the hose to a Marine Craft as Boat Safety Inspectors will be looking for clearly marked Marine compliance.
Cohline DIN 73379 Type 3E (Rev. 11/97) is being supplied by a few companies as "bio safe" hose. We have a datasheet from Cohline here. It is of standard inner/outer construction as per tradition for fuel hoses. The inner is FKM and the outer is ECO. Based on this construction we can assume it is to a similar standard as the Codan SAE J30 R9 hose that we currently sell at Volksbolts which also uses the FKM liner material. The Cohline data sheet also states that the DIN 733979-3E hose is conformant with SAE J30 R9.
What is becoming apparent from our research around the subject is that the SAE J30 R9 and R14 standards are becoming dominant, with competing national and industrial standards becoming subservient to SAE for setting the de-facto for qualitative expectations.
Fuel Hose Size (Bore) Selection
It is of EQUAL importance to select a fuel hose of the correct inner bore diameter (ID) as it is to select the correct fuel hose grading.
One of the properties of Rubber materials is its elasticity; The ability to be stretched and to recoil back to its original shape. The material essentially behaves like a spring. This 'elastic' spring force acts with the natural friction generated between the fuel hose and the metal stand-pipes when the rubber fuel hose is stretched over the metal pipes (Inlet banjos on fuel pumps, filters carburetors etc.). This generated 'grip' under normal operations will hold the fuel hose in position on the pipes (Similar to the way a rubber tire grips the road).
This is shown in the picture below - based on the Vintage vehicle application of 5.5mm/5.6mm modern ID fuel hosing onto the 6mm / 7/32" OD metal stand pipes of the fuel delivery system. The magic number for the amount a hose should stretch is 10% max (increase circumferentially) - confirmed in our conversations with Codan Rubber and and other elastomer experts, represented in the diagrams below with 7% nominal circumferential expansion:-
And for DellOrto carburetor 8mm "bulge" hose inlet connections :
Fuel Hose Clip Selection
An ideal clamp will generate a UNIFORM clamping Force around the fuel hose, with this evenly applied Force helping the fuel hose to form a nice tight seal.
It is important to choose and use hose clamps properly. Hose clamps are sized to fit specific diameters of fuel hose and should only be used for those fuel hose sizes. Inappropriately sized clamps will not perform as specified and will apply Force around the fuel hose unevenly.
There is a popular myth of worm and band clamps (Jubilee brand clips) ovalising when tightening and therefore they should not be used on fuel hosing. This myth is almost certainly fueled by people using inappropriately sized clamps; Though it is in part true
We can support this by comparing the 'Spider' diagrams of clamping Force below : To the left is an IDEAL distribution : To the right is a MEASURED distribution (Worm and band clamp...data courtesy of Norma Group).
As can be seen, tightened clamps provide a slightly ovalised clamping Force by design. This applies to all clamps with a single tightening mechanism. The Force is lower on the rear side of the clamp due to frictional loses between the rubber hose and metal clamp as the clamp is tightened.
This effect is not problematic; These clamp styles are used in safety conscious Marine applications throughout the World. They are manufactured to BS5315, have BSI KITEMARK & N.A.T.O. approvals & hold Lloyd's Shipping Register approval.
SELECT THE MOST APPROPRIATE DIAMETER OF CLAMP FOR THE HOSE YOU ARE SECURING
Clamps should be Torqued properly to assure a good quality seal - for captive nut and screw (Such as the ABA fuel hose clamps in the picture above) & worm and band clamps (Jubilee or JCS Hi-Grip)
Check the metal fuel connection on carburetor, fuel pump and fuel tank
With the increasing age and wear & tear taking its toll on Air-Cooled VW designs, people are encountering age related issues at an increased rate.
One issue of specific concern is the wear & tear on the press fit metal stand pipes on the VW fuel pumps & carburetors.
As can be seen in the below photograph : these press fit parts can work loose and pull out of the Aluminium castings.
If this happens on a running engine the results could be catastrophic : regardless of whether you have used the correct fuel hose & clips.
To check simply give the pipes a 'wriggle' : any looseness should be obvious.
The best repair advice we have Can be summarised as below :
Replace the entire fuel pump or carburetor with a new unit.
Refit the pipe using a strong Loctite compound.
Tap the casting and use a threaded fuel hose fitting of appropriate size.
Other Useful Resources and Articles:
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