Diesel Fuel Tank Replacement Advice

[Concordia]

Folks - Replacing one of three rusted-through diesel fuel tanks in my cutter. It is on the starboard rail and holds approximately 28 gallons. Debating replacing with epoxy coated steel, aluminum or stainless steel. For those that have done this, what material did you use. How thick and grade of material? Did you stick with a traditional sight tube or go with a mechanical fuel gage?
Thanks in advance.

[Jammer]

Mine is aluminum but my advice would be to use whatever's cheapest. Any material will outlast your likely use of the boat.


I have an electromechanical gauge for my diesel tank but may switch to using the more trustworthy tank tender that is presently set up for measuring water and waste only.

[coopec43]

I have aluminum tanks.

I've bought glass tube and fittings (including tap) to plumb into the tank but haven't done so at this stage.

If you use a bit of clear plastic tube as a "sight glass" many marinas will ban entry to your yacht as it would be considered a fire risk. Others would require a tap to turn off the flow of fuel if the glass sight glass broke.

I'm sure the Johnson site glass has approval but last time I checked they were around $A120

[Pete7]

If you can find a suitable sized roto molded plastic tank that may be the cheapest. More over you can see through translucent white plastic even if it quite thick to see the fuel level.

Pete

[Tupaia]

Originally Posted by Pete7

If you can find a suitable sized roto molded plastic tank that may be the cheapest. More over you can see through translucent white plastic even if it quite thick to see the fuel level.

Pete

I vote for this also, even custom made they are reasonably priced and allow for proper cleaning if you experience "bug" quite common these days with bio content in diesel.

[GrowleyMonster]

Translucent polyethylene doesn't need a sight glass, as indicated by posts above. All you need is good lighting.

If you go for an opaque material, my vote is to keep it simple. If there is any way possible to install a deck fill fitting right over or nearly right over the tank, you can just sound the tank periodically with a bamboo pole, yardstick, sounding tape, whatever. If that is not physically possible or practical, I would go for a mechanical gauge before any electric thingamabob. It's not a dealbreaker or anything, just my preference.

Sight glasses definitely need an isolation petcock top and bottom and they should be left closed except when you want to read the level in the tank when it has changed.

[coopec43]

Originally Posted by Pete7

If you can find a suitable sized roto molded plastic tank that may be the cheapest. More over you can see through translucent white plastic even if it quite thick to see the fuel level.

Pete

I don't know whether this is relevant.

But before you start filling plastic drums with fuel, you need to check that the drum is designated as suitable for use as a plastic oil drum, and that it was manufactured from HDPE. Not all plastic will hold diesel fuel effectively, without contaminating the fuel or being rapidly broken down.
Once you have an industrial standard plastic oil drum, you still need to consider how long you can safely store the fuel for. Unfortunately, you can’t store diesel fuel in plastic drums forever. The diesel will react with the plastic polymers over time, even if the drum is produced from HDPE. The plastic will then break down, eventually leading to leakages. The diesel fuel can also start to break down and become no longer fit for purpose.
Government guidelines recommend that diesel fuel be stored for no longer than six months. After this, you need to change your drum and dispose of your diesel fuel. Other factors can also affect this limit. For instance, extreme heat or temperature changes will degrade the fuel faster

https://itppackaging.com/is-polyethy...l-fuel-storage

[GILow]

Originally Posted by Pete7

If you can find a suitable sized roto molded plastic tank that may be the cheapest. More over you can see through translucent white plastic even if it quite thick to see the fuel level.



Pete

One more vote for this approach. So many shapes and sizes to choose from, plus many manufacturers allow you to choose the number and position of fittings for fillers and pickups.

[GILow]

Originally Posted by coopec43

I don't know whether this is relevant.

But before you start filling plastic drums with fuel, you need to check that the drum is designated as suitable for use as a plastic oil drum, and that it was manufactured from HDPE. Not all plastic will hold diesel fuel effectively, without contaminating the fuel or being rapidly broken down.
Once you have an industrial standard plastic oil drum, you still need to consider how long you can safely store the fuel for. Unfortunately, you can’t store diesel fuel in plastic drums forever. The diesel will react with the plastic polymers over time, even if the drum is produced from HDPE. The plastic will then break down, eventually leading to leakages. The diesel fuel can also start to break down and become no longer fit for purpose.
Government guidelines recommend that diesel fuel be stored for no longer than six months. After this, you need to change your drum and dispose of your diesel fuel. Other factors can also affect this limit. For instance, extreme heat or temperature changes will degrade the fuel faster

https://itppackaging.com/is-polyethy...l-fuel-storage

No, it’s not.

[coopec43]

I'd like to think HDPE tanks last indefinitely but:

"Plastic fuel tanks usually last for approximately 10-15 years – but can last up to 20 years when properly maintained. This longevity is commonly backed up by a 10-year warranty in the case of many major fuel and oil tank manufacturers."

https://rpm-fuels.co.uk/helpie_faq/w...tic-fuel-tank/

If that is true then HDPE are not a proposition. But then how long will an aluminum or SS tank last?

Marine Fuel Tanks - Plastic Vs Aluminum
https://www.reviewwarehouse.com/mari...nd-cons-debate

[Jammer]

Until corrosion gets them. Not forever. Stainless probably longer than aluminum of the same thickness. In either case you want to keep them properly supported and dry on the outside, and keep the diesel clean and free of water.

[boatpoker]

Originally Posted by coopec43

I'd like to think HDPE tanks last indefinitely but:

"Plastic fuel tanks usually last for approximately 10-15 years – but can last up to 20 years when properly maintained. This longevity is commonly backed up by a 10-year warranty in the case of many major fuel and oil tank manufacturers."

https://rpm-fuels.co.uk/helpie_faq/w...tic-fuel-tank/

If that is true then HDPE are not a proposition. But then how long will an aluminum or SS tank last?

Marine Fuel Tanks - Plastic Vs Aluminum
https://www.reviewwarehouse.com/mari...nd-cons-debate

Either will last indefinitly if maintained, designed and installed properly. My first boat is still out there with 51 year old ss tanks. My second boat is still out there with 41 yr. old aluminum tanks. Both had fuel feed from the bottom so that water never sat in the tanks but went to the fuel filter. When I replaced my rusty steel tanks 2yrs ago with aluminum, I had them built with feed from the bottom.

[coopec43]

Originally Posted by Jammer

Until corrosion gets them. Not forever. Stainless probably longer than aluminum of the same thickness. In either case you want to keep them properly supported and dry on the outside, and keep the diesel clean and free of water.

Yes! "want to keep them properly supported".

If you place an aluminum tank straight onto timber condensation between the tank and the timber will cause corrosion. I'm hoping I have avoided that possibility as I sikaflexed plastic strips onto the tank where they are mounted on timber.

[boatpoker]

Originally Posted by coopec43

Yes! "want to keep them properly supported".

If you place an aluminum tank straight onto timber condensation between the tank and the timber will cause corrosion. I'm hoping I have avoided that possibility as I sikaflexed plastic strips onto the tank where they are mounted on timber.

A smart move to avoid poultice corrosion and something the builders often overlooked.

[PUDDLE JUMPER II]

Just had two SS 316L made for the boat as my original tanks were 42 years old, and were made from thin 20ga stainless steel.

I had the exact replicas made from 16ga SS... They will outlive and outlast my lifetime and the boat. After welding-- I had them pickled old school style.

My advice-- bring the tank to two Fuel Tank shops that MAKE them--- and NOT to a welder around the corner. There are too many tricks of the trade in welding something that you expect to function 100% + outlast your lifetime that plain old welders just do not have experience that a fuel tank welder would have. You get what you pay for -- this also relates to the experience of who you hire. The right resource for a skilled job...

Good luck!