Replacing my fuel system; material and hoses

[JordanH]

Hi folks,
I have a 1983 Contessa 26; It has the original Farymann K34 which still runs well. The steel fuel tank, on the other hand, has rusted, been filled with goo several times over the years I have owned it, and, well, it's gotta go.


I have a beautiful, new, aluminum tank that I designed myself and had Boyd Welding (Florida) build for me. I will be replacing all parts of the very simple fuel system from tank to engine and have a few basic questions.

Q1. New tanks is aluminum and I had 3/8" NPT ports fitted for vent, return and pickup. I now need to buy the actual fittings... What material should I use? My first thought is that brass is "best" but will suffer galvanic corrosion.
What material should I use for the fittings at the tank?

Q2. Secondly, the engine is vacuum fed. At present, I believe the hose is different sizes between the current tank and fuel filter, compared to the fuel filter to the engine. Is there any problem with "upsizing" the hoses so that they are all the same diameter? And if the hose is larger, will that impact the ability to siphon fuel from tank to engine? Larger makes it easier, right?

Q3. The old fuel filter is pretty basic. I'm thinking of adding one or two other components but I'm not sure what effect that will have on the siphon. In theory, nothing, but my experience is any time you add something to a simple system you introduce areas of failure. What would you put in?
- Presently Tank --> Fuel filter --> Engine. (No inline prefilter, no water separator)
+ I'm considering adding a Racor water separator.
+ I'm considering adding an inline prefilter that would handle larger chunks... 3 times burned with algae and rust in the tank has me overly cautious about crap in the tank getting through.

Bonus question... Anyone care to guess what the "right" size of fuel hose should be? (Old engine has had multiple owners who have done many projects. I have no idea what hose size I *should* be using, only what the previous owners have used.) Remember, this is a single cylinder, 7hp diesel that uses about 1.3L/hr (about 1/3 Gallon per hour) so it's not a lot of fuel or pressure.


Cheers,
Jordan.

[Compass790]

I don't know what the right size in theory is but our yanmar 8hp uses 6mm ( 1/4" ) fuel lines with no problem part of the way from the tank then they change to 8mm ( 5/16" ) before primary filter with no problems for the lift pump but upsizing so they are all the same as you wish to do would be ideal.

I would be tempted to see if you can get aluminium fittings for the tank. Agree it's a good idea to have a water seperator type coarse ( maybe 20micron ) primary filter then a finer say 10 micron or less final filter. The other thing I'd suggest is use a filter funnel when doing tank fills as i'm constantly surprised how much crap comes in fuel.
You should have minimal problems with a new tank though

[JordanH]

For what it's worth, here is a picture of the tank... errrr... 'installed' in my front hallway. (No other reason than to show how nice it looks)

The more I think about it, the more I'm convinced aluminum is the way to go too. I guess the only other question is, do I require a different type of sealant for aluminum vs brass fittings... hmmm.

I do have a filler port installed, and I do have a deck-mounted filler. But it has been the cause of my algae problems in the past. And, well, I probably don't even use a tank of fuel every 5 years. I'm considering not installing the filler pipe until I pull out the old filler cap.

I agree with you that a lot of crap comes in from fuel...It's an old boat, an old engine. The benefit to cost ratio might be decreasing with too many extra add-ons.

[Compass790]

Beautiful! Boyd is a good welder.
Any hydraulic pipe sealant will work on your ali fittings should you find any. Some anti-algae treatment would not be a bad plan if a tank of fuel lasts for 5 years.

[rbk]

I would be adding an additional pick up and return line and install a separate simple fuel polishing system, sounds like you need one. No pickup pre filter/screen, keep all filters out of the tank. Last thing you want to do in weather is have to open your tank to clear a blocked screen. Racor 500’s do both water and dirt. Two of them, one on polish duty other on the engine. You could get fancy and make them interchangeable or ability to run in parallel, but like you said more parts. 1/4” A1 should do and keep it all the same, don’t jump up or down sizes.

[dcstrng]

I’m thinking of a similar path – my aluminum-appearing tank is fine, so far as I know, but the look of the elderly fuel lines and filtration doesn’t inspire confidence… My thought was to use aluminum AN fittings and appropriate aluminum tubing for solid portions and then marine grade fuel lines (with AN adapters) for those transition portions requiring flex… I also plan to move to a Racor or similar filer/separator as the tiny filter in my 15hp Yanmar looks like it is what is on my lawn-mower…

Am not sure this is the right approach, but since aircraft and speed-shops are closer to what I know, it is where I’m thinking, at least at the outset… I am concerned of the galvanic issues, but was thinking that aluminum to aluminum should reduce that, and then use marine-rubber to the steel portions which should help maintain some isolation. But, I could be way off base…

[JordanH]

Compass790... yeah, I have combatted the Anti-Algae stuff for a number of yeras. It all started when the fuel attendant didn't completely screw down the filler cap and I washed the deck shortly after. Water ran straight into my old steel tank, but without inspection hatches, there really wasn't anything I could do to get it fully cleaned out where I was. A few weeks later, it was full of gunk. Needless to say, I've cleaned it out, put in algae cleaner, stabilizer, been through uncountable fuel filters since. In addition to this, the steel tank has been flaking rust which were being picked up in the pickup and blocking the hole... the engine would die, and the rust would fall away, allowing me to restart again. Rinse wash repeat.

The whole goal of this is so that I don't have these issues in the future; I went aluminum tank so I (and the next owners of the boat) will never have rust issues, I put an inspection hatch in place so it can be cleaned. Instead of a giant 46 litre tank, I reduced the size... I can't remember, maybe 30L now, to reduce the age of fuel in the tank. (I also changed the horizontal tank to vertical tank for less sloshing and better performance while motorsailing. But I digress.)

RBK, that is a good idea for a second set of ports for fuel polishing... I should have thought of that. Then again, it's only 30L so not a tremendous deal to empty, clean out and replace without polishing.

As for the comment about screen in the tank... no, that's not what I meant. Someone had suggested
Tank --> inline "filter" (screen in hose) --> fuel filter --> Engine
Instead of the cheap inline filter, I have considered a variety of systems including multiple parts... but then I realize that they are generally way over kill for my boat.


dcstrng, a mechanic friend of mine suggested hard lines. I'm not a fan of anything "hard" on a boat, not for plumbing or electrical anyway, so I am skeptical for hard fuel lines when the boat may flex and wear any joints. Also, it's not a straight run from tank (starboard) to intake (port)... the less 90 degree corners I have the better for flow. Maybe that's nothing.


At any rate, I appreciate all these thoughts.

[tkeithlu]

I doubt that brass fittings will pose a problem in that environment; it's oil, not sea water as an electrolyte. Plumber's goo dissolves in diesel, so be careful that you don't use too much. Copper tubes are fine as long as you don't work harden them with fibrations; if it is short runs, go with hydraulic hose. Sounds and looks like a beautiful system.

[dcstrng]

Originally Posted by JordanH

I'm not a fan of anything "hard" on a boat, not for plumbing or electrical anyway, so I am skeptical for hard fuel lines when the boat may flex and wear any joints...

Yes, thanks... I've wondered about that -- metal tubing can last for a very long time even in a high-vibration environment, if properly supported -- but marine fuel hose seems to have a very long life if properly cared for as well -- and generally easier to install. Generally we use metal lines for runs where there is limited access, snce it is p[resumed that fuel hose needs to be redone every 4-7 year (aircraft) but my fuel line runs are generally easy to get at, so I'd think that is another argument for marine hose (FYI real marine fuel hose is thicker and has modest fire resistant properties that are not as apparent with auto/aviation fuel-injection hose... )

Thanks; I may have talked myself into using hose...

[Boatwright]

Aeroquip makes a complete line of aluminum and ss fittings. These are readily available from auto parts suppliers. Most of the aluminum tanks I see are using ss which is not bad electrolitically. Definitely don't use brass.

They also have field assembly fittings to use with stainless braided cover hose. Does anyone know if this aircraft approved stuff is also OK with the Coast Guard for marine use?

[bad.wabbit]

Our aluminum fuel tank has 1/2 female npt threads and the OEM used st. steel bushings to get to 3/8 brass barbs. 40 years an DC no corrosion. I had some stainless tubing welded onto the bushing to create an extra pickup tube when I needed one. A great selection of npt,barb fittings, and Raycor type is https://www.hoseandfittings.com (no affiliation). I just looked and they have AL npt to barb...

[Dougtiff]

You need to use Stainless steel fittings on the tank, then hose to the filters, just did this for a customer, also a Ground / bonding wire to satisfy the surveyor.

[sanibel sailor]

Use aluminum fittings. Anything you can want at McMaster.com
I replaced my tank and all components about 8 years ago and Racor remains pristine. I changed the filter once but didn't need to.
Make sure your fill cap O-ring is good. I believe that is where most water gets in fuel. Keep the water out, no algae. No algae, no need for polishing, etc. 1/4" hose and a small Racor is quite sufficient for your small requirements.

[Dranflydbl]

For what it's worth Jordan, we use aluminum lines and fittings all the time in aircraft fuel systems. Suppliers like Aircraft Spruce can generally provide suitable screw on fittings and suitable olives for aluminium fuel lines.