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Low pressure fuel hose size? - K Series

One of my fuel hoses is leaking. Does anyone know the size, my guess is 8mm ID?

It is for an EU3 VVC and is the short (about four inches) section of rubber hose that connects at the front of the plenum to a shiny nylon hose via jubilee clips. It is referred to in the build manual (9.7) as "flexible rubber hose".



Yes 8mm bore. I think you're referring to the fuel return. I replaced the same this year as it had gone very rigid. Got the tank end to do as well.

I used a local hydraulic hose & pipe place who were very reasonable. Remade the fuel inlet hose using my original fittings for under a tenner.


Thanks. I've just removed it and it is clearly marked on the reverse side 5/16" 15082 so 8mm will be fine.

My inlet hose went a few years ago and was also made up for a good price. I think I need to have a ferret around the tank next as there must be something around there that is on borrowed time.

I think a meter should do the tank bits as well. I got an aero cap for my birthday so am changing the main rubber tank connection, the 16mm ID filler neck to tank hose and all the 8mm returns / breathers.

I had to buy a meter of the 16mm stuff so can post a bit if you want some.



I fitted an aero cap a couple of years ago and at the time all looked well. A casual look hasn't highlighted any problems but I'll have a closer look and probably swap out the lot. About time I did the filter as well while I'm about it.

Thanks for the hose offer but I should be okay with sourcing parts it is knowing which part to ask for that usually stumps me.



Do make sure you get the latest spec fuel hose that resists ethanol.

What spec should that be? What markings should we be looking for?


Petrol for road vehicles that's currently available in the UK is up to 10% ethanol. Anything that's sold new for use as a petrol hose should be OK. (IIRC the key date was 1988, but I can't find the recent thread.) 


Recent stuff I bought SAE J30 R9 7.6mm Fuel injection. Avoid the cheap cotton covered hose. Get one with a nice thick wall.

I may have posted this before (from SELOC IIRC....) but it's worth a read.



Results of research

* Petrol has changed significantly over past few years - it now contains more alcohol-based substances, which are very corrosive to normal rubber.
* Hoses in the USA are marked with an SAE code, e.g. SAE J30R9, according to its ability to resist modern fuels. As much of the hose bought in the UK is made (or sold) in the USA then these markings may appear here.
* There are 4 significant groups of SAE codes:
Unmarked hose - will probably be for the original petrol formula, without modern additives (but see later comments).
30R6 - This is the standard for the petrol formula of 5 - 10 years ago, for fuel injection. The bore may or may not be lined with Nitrile.
30R7 - This is the standard for the petrol formula of 2 or 3 years ago, for fuel injection. The bore is lined with Nitrile.
30R9 / 30R10 - This is the current standard. The bore is lined with Fluoroelastomer/Nitrile. 30R9 has Fluoroelastomer/Nitrile on the inside, while 30R10 has it inside and out, which allows it to be used immersed in petrol (e.g. in a fuel tank).
* There is also a marine grade for use in boats - ISO 7480 A1 - that is roughly equivalent to 30R7-and-a-bit, with added fire resistance.
* One of the causes of fuel pipe failure described in the USA literature is stale modern fuel, not so much the fuel itself. These fuels become extra-corrosive when they get old.
* The USA seem to use a higher percentage of alcohol in their regular fuel - but we're not far behind in Europe.

What got me angry...

* Gates in the USA only make and sell fuel pipe of grade 30R9 or better (they even have brand-new super-grades). Gates in the UK distribute unmarked hose to motor factors that, if you are lucky, is only 30R6. Why don't we get the same? Are they dumping their surplus stock on the UK?
* The Gates sales rep for the UK and Europe didn't know that the USA grades were far higher than his offerings - he didn't even know the trade names for the USA products (shown in every USA Gates catalogue).
* 30R9 is freely available on the USA ebay, at sensible prices, made by big-name manufacturers such as Gates and Goodyear. It is never (or maybe rarely) available on the UK ebay. Only the excessive postage stopped me from buying it there.
* One on-line supplier (Think Auto) advertised that their hose is 30R9, but when it turned up it was unmarked. I recognised that it was stuff that I'd used previously and told them so. To their credit they apologised, refunded my money AND paid for the return postage.
* There is a general ignorance about this whole issue - when I asked for a specific grade of hose many suppliers didn't comprehend, while others were almost abusive ("Our stuff is good enough...!).
* The one who did supply the correct hose, Hose World, advertised it as 30R10 on their website, the bloke on the phone didn't think it was any special grade when I asked, and when it turned up it was 30R9, which is what I was after in the first place!
* If you search on any USA car forum about fuel pipe you will see that most people are fully aware of this issue, and the need to use modern hose. There seems to be a general ignorance in the UK.

Last thoughts and recommendations
It was almost certainly stale fuel that rotted my fuel pipe(s).
1. Don't buy general-purpose hose from a motor factor, unless it has at least 30R9 printed on it. Even stuff off the Gates stand isn't good enough.
2. If you are getting it via the internet or mail order, don't be fobbed off by excuses. Only the proper stuff is safe for long-term use.
3. If you are going to leave your car unused for a month or so, consider draining the petrol, especially if you are unsure of your fuel pipe grade.
4. If you really can't get 30R9, consider getting ISO 7480 - this is easily available from marine suppliers in the UK (but see point 3). All proper fuel pipe in this grade has to be marked, to meet regulations.

It might help to add to add the relevant fuel compositions (E10, E50, E85 etc) to that analysis.

* Gates in the USA only make and sell fuel pipe of grade 30R9 or better (they even have brand-new super-grades). Gates in the UK distribute unmarked hose to motor factors that, if you are lucky, is only 30R6. Why don't we get the same? Are they dumping their surplus stock on the UK?

I don't think that there's any reason to suspect malevolence or malpractice. And the lead times for introduction of new fuel compositions have been very long.


But the main points are that problems are very rare with commercially available fuels except with old hoses and non-mainstream products. And that fuel hoses, seals etc should be treated as consumables for vehicles that survive as long as many 7s.