PSA - Effect of ethanol blended fuel on fuel hoses

[raueda1]

A year of so ago I discovered that the small, curved fuel hose between the fuel pump and accumulator had pinhole leaks and was spraying fuel.    The hose was just a few years old and had failed in that time.  It turned out that the hose liner was all cracked.  Since then I did some digging into the effect of ethanol fuel blends on fuel hose materials.  The bottom line is this:  modern hoses (say late 80's to present) use several materials.  The inner hose liner is often nylon or a fluorinated elastomer like Viton, etc.  This stuff resists ethanol in the fuel.  Older hoses, such as what we're used to in the W116 era, typically used a nitrile (NBR, Buna-N, etc) liner and neoprene jacket.  Nitrile has excellent resistance to hydrocarbons.  It does NOT have resistance to polar solvents, such as alcohols, ketones, etc.  Immersion in ethanol fuels causes far more softening and swelling than in straight hydocarbon fuels.  There are countless publications on this by hose makers, rubber producers etc.  It is not a secret.  On top of this, the design of the fuel delivery system, with that tightly curved hose,  makes things even worse. Tightly curved hoses like this make a worst case scenario - one side is in constant compression while the other is under constant tension (stretching).  Everything bad that can happen to rubber is aggravated by compression or tension.  The design should really use elbows or steel fittings.

Despite this, many of us assume that a fuel line will last more than a couple years.  And we are forced to use ethanol/petrol blends.  In my area ethanol-free fuel isn't available at all.  This seems strikes me as a perfect recipe for disaster.  What to do?  Well, first of all it seems like common sense to regularly inspect these fuel lines.  Even better would be to fabricate new ones using better materials.  That's my plan.  Happy motoring and cheers,

[Neil4speed]

Thanks for sharing. I have a real fear of having a fire due to a fuel leak.

[daantjie]

Good practice to always keep a fire extinguisher in the car just in case.

[revilla]

Or, you could simply resource to MB original upgraded (and safer) version with rigid tubing instead of elastomers hoses. They figured that problem out on their own and implemented the better design circa ~1978 not just for W116 but also for W107 and perhaps other models.
First 3 pictures: hose design
Last picture: tubing design

[Jan S]

I'm glad we get ethanol-free super 98 RON in Norway 

[Randys01]

91...95...98 Lead free Ethonal free here in Aus ...but some places do a 94 10% Ethenol.

[andrewk]

I'm glad we get ethanol-free super 98 RON in Norway 

The benefit of having a very healthy hydrocarbon industry, and no spare land for growing grain to make fuel ethanol (which is actually less energetically efficient than using hydrocarbons - you need to grow the grain, fertilise the soil, use Diesel to harvest and transport the grain, ferment it then use coal, gas or electricity to distill it - mostly on a smaller scale than oil refining - then you have to transport the ethanol to the blending site, also with Diesel). We have 98 RON here in Australia but it's currently $2.09-2.69/L which is a little spicy.

As for that hose. I installed a replacement, genuine Mercedes Benz hose in my car during my fuel system overhaul. When the air temperature is above 25*C (most of the time here, it seems), the crimped fitting weeps fuel - my guess is the head pressure of vapour in the tank is forcing it out of a damaged area. Something to monitor, even with new hoses. I'll replace it with a new part which just arrived from Classic Center and monitor this regularly over the summer. Long term plan will definitely be to use a hard line, as found on the W126 560 SEL and other models.
Tight bend radius, braided multilayer hose and crimped fittings is not a good combination. Ethanol will rapidly degrade older types of rubber hose to the point where the rubber turns rock hard and cracks. I have seen this a lot.
Thanks for the timely reminder, Raueda1. Fuel is just about the most dangerous thing most people encounter in their day to day life. It's dangerous because it's safe most of the time, but potentially catastrophic when it does go wrong. Complacency is a big issue with automotive fuel systems. "She'll be right mate" (an often uttered Australian saying) no replacement for regular inspection and maintenance.

[mrkozzy]

Thanks to everyone for this very informative piece of information.

Who would've thought?

Can anyone supply a brand, part number or supplier of these "Non Rubber" alternatives mentioned in this article.  I'd love to order one immediately.

I'd be looking at a UK or European supplier as I'm in Ireland.

Thanks

[revilla]

1234702264

[raueda1]

Or, you could simply resource to MB original upgraded (and safer) version with rigid tubing instead of elastomers hoses. They figured that problem out on their own and implemented the better design circa ~1978 not just for W116 but also for W107 and perhaps other models.
First 3 pictures: hose design
Last picture: tubing design

Amazing, thanks much.  I'll be getting one as well.  And yet it's kind of strange that all the vendors out there still supply the lousy rubber hose.  I've never seen the improved versions anyplace.  Cheers,

[revilla]

Or could be this one depending on your fuel package, with or without check valve, one inlet type accumulator.

1264700164

[marku]

That's going to apply to the injector hoses as well isn't it.

[ptashek]

We have 98 RON here in Australia but it's currently $2.09-2.69/L which is a little spicy.

We pay about 40c more per litre of 95-E10 in Ireland. I've seen 98 for as much as AUD 3.85/l in France just a couple months back.

Count your blessings

As for fuel hoses specifically - look for SAE J30 R9, as opposed R6, ones. The R9 are specified for biofuels, and have a much higher resistance to ethanol.

[raueda1]

Or could be this one depending on your fuel package, with or without check valve, one inlet type accumulator.

1264700164

I'm struggling to find the single (i.e., 2-ended) part pictured that replaces the rubber hose. All that I can find from usual suppliers is the rubber hose design.  1234702264 seems to be the 3-ended solid tube version.  Does anybody know the PN for the solid line that replaces the rubber hose version? Thanks and cheers,