Modern Gray Fuel Hose: friend or foe?

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
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Modern Gray Fuel Hose: friend or foe?

Postby GoldenDaze » Fri Jun 28, 2019 10:20 am

There's certainly been plenty written about the evils of gray fuel line, how it disintegrates, and how it causes all sorts of problems. Some say that's still the case, while others contend that modern gray fuel line doesn't have these problems. Here's a look from my own experience with my 2003 160 Dauntless, which has a 45-gallon internal tank and a below-deck canister fuel filter.

Every year I replace my primer bulb with an OEM Mercury replacement. About every five years I also replace the fuel line from the primer bulb into the engine. Finally, every eight years—when I'm in the mood for a particularly difficult job and have an urge to get covered in gasoline—I replace the entire fuel line from the tank through the below-deck canister filter to the engine.

This year I had that urge.

For the fuel line from the tank to the canister filter and from there to the primer bulb I have always used Shields Series 368 3/8" ID hose. This is a heavy-weight, thick-walled hose that's not particularly flexible but it has always stood up very well to use including 10% ethanol fuel. It has a thick rubber wall with nylon reinforcement and a very thin inner liner. The inner liner has never shown any sign of degradation or delamination, and while the photos below are of a new piece of fuel line, the 8-year-old fuel line looked exactly the same. I think it could go for years and years with no problems.

Fig. 1. Shields Series 338 fuel line (new).

Fig. 2. Shields Series 338 fuel line end (new). Note the nylon reinforcement embedded in the rubber and the thin inner liner.

Fig. 3. Shields Series 338 fuel line section (new). The inner liner seems strongly bonded to the outer hose.

Unfortunately the Series 338 fuel line has an OD of about 17mm or 11/16", which is too large to pass through the rubber grommet into the engine. So from the primer bulb to the engine I have in the past used Sierra Silverado 3000 3/8" ID fuel line, which is termed "above deck" fuel line by the manufacturer. Silverado 3000 has a shiny gray outer later and much thinner walls than Series 338 with an OD of about 13.5mm or 17/32", making it much more flexible. In fact it will kink if you're not careful about the run. The fuel line has no visible nylon or other reinforcement, but it does have a fairly thick clear plastic inner layer. This year when I disconnected the line from the primer bulb, I found that about 1/4" of the inner liner had delaminated from the outer hose and was pushed up into the fuel line, mostly blocking it. It's a testament to the Mercury 115 EFI four-stroke's stingy use of fuel that it was able to run happily with such a restricted fuel flow. Unfortunately I threw that section of hose away before I thought to write this article, so I don't have a photo of it. The liner did remain in one piece however, and there were absolutely no fragments or plastic goo in the on-engine fuel filter bowl. Still I have to conclude that this is pretty terrible stuff and should certainly be avoided. Silverado 3000 -- definitely FOE.

Fig. 4. Shields Silverado 3000 fuel line (about 5 years of use). Note the glossy outer surface.

Fig. 5. Shields Silverado 3000 fuel line end (about 5 years of use). Simply cutting through the fuel line was enough to start the liner peeling from the outer tubing.

Fig. 6. Shields Silverado 3000 fuel line section (about 5 years of use). The inner liner eagerly peels away from the hose.

This year I was able to get some different "above deck" fuel line, Shields Silverado 4000, also in 3/8" ID. This hose has a matte gray finish and is easily distinguished from Silverado 3000. It is slightly thicker with an OD of about 16mm or 5/8". While that's not a lot narrower than the Series 338, it still fits through the hole in the outboard grommet. Silverado 4000 is much more flexible than Series 338, but not so flexible or prone to kinks as Silverado 3000.

Fig. 7. Shields Silverado 4000 (new). Note the matte surface. Lighting conditions make the hose look darker than it really is.

Fig. 8. Shields Silverado 4000 end (new). Note the thick black rubber liner that is interlocked with the outer hose using jigsaw-puzzle-like protrusions.

Fig. 9. Shields Silverado 4000 section (new). It appears that the interlocking protrusions between the liner and the outer hose are both radial and lengthwise. I don't think that inner liner will be separating any time soon.

Of course, I'm just installing the this new fuel line now, so I won't know for a few years yet how it holds up, but it does look like a substantial improvement over the previous version. Silverado 4000 -- maybe friend?

2003 160 Dauntless Golden Daze

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Re: Modern Gray Fuel Hose: friend or foe?

Postby jimh » Wed Jul 03, 2019 2:59 pm

BOB--your article is a masterpiece. You have my deepest appreciation for the time and effort to discover this information and to present the information in an outstanding manner.

The separation of the inner line from the outer jacket that you show in Fig. 6 above is the best evidence if the inferiority of that type of fuel hose for use with modern gasoline blends. My local outboard engine dealer has shown me similar silver-metallic fuel hose with the the identical problem.

The general caution to be suspicious of fuel hose with a silver-metallic cover is well-founded and nicely demonstrated in your article.

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Re: Modern Gray Fuel Hose: friend or foe?

Postby dtmackey » Sat Jul 06, 2019 9:50 pm

Not all gray fuel line is created the same and over the years it's varied from manufacturers. I've been using the Shields gray fuel line in two boats with no problems. It's not the same as the junk that had the liner that collapsed and caused people to classify all gray fuel line as garbage.

The cutaway pics are great.


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Re: Modern Gray Fuel Hose: friend or foe?

Postby FL21WAC » Mon Dec 30, 2019 9:31 am

I second the appreciation for the effort and quality of the original post. I am undertaking fuel line replacement and this thread is very helpful to me.

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Re: Modern Gray Fuel Hose: friend or foe?

Postby VKR » Mon Jan 06, 2020 10:25 pm

The Silverado 4000 fuel line exterior matte color, interior appearance, cross and longitudinal section appearance is very similar to the appearance of the Trident B1-15, SAE J1527 hose. Given the similarities, I thought for sure the Silverado 4000 hose was made by Trident Marine, but a quick search shows the Silverado 4000 being manufactured by SeaStar Solutions.

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Re: Modern Gray Fuel Hose: friend or foe?

Postby L78steve » Wed Jan 15, 2020 12:44 pm

Thank you for this info. Checked all my hoses and they are all the 4000-series.
1988 15' Sport, 89 Johnson 70HP
1998 22' Progression Merc 300XP
1961 12' Allstar FG 73 Evinrude 25