Plastic Gas Tank

[Ogden2]

Does anyone know if or how much my plastic gas tank will expand and contract and how much clearance it needs in the compartment? It's a 26 gallon tank and it has about a half inch on either side (not including the rubber bumpers which basically touch the tank) and between the cross boards on top of it and the top of the tank there is about an eighth of an inch (only in two spots, the rest of the top of the tank has about an inch and a half under the floor).

Thanks for your help.

 

[duke33]

Re: Plastic Gas Tank

It should'nt swell if vented.

 

[Ogden2]

Re: Plastic Gas Tank

Very good. Thanks!

 

[Grandad]

Re: Plastic Gas Tank

Moeller's installation instructions state that plastic tanks expand in all directions by about 3%. I believe this is due to hydrocarbon saturation or something or other beyond my knowledge. This is not just thermal or internal pressure expansion. 3% is about 1/2" on an 18" section, so it's worth considering. When I remounted my plastic tank after about 5 years of use, its 16 1/2" width had expanded about 1/4", so I had to oval the mounting holes to suit. - Grandad

 

[Ogden2]

Re: Plastic Gas Tank

Moeller's installation instructions state that plastic tanks expand in all directions by about 3%. I believe this is due to hydrocarbon saturation or something or other beyond my knowledge. This is not just thermal or internal pressure expansion. 3% is about 1/2" on an 18" section, so it's worth considering. When I remounted my plastic tank after about 5 years of use, its 16 1/2" width had expanded about 1/4", so I had to oval the mounting holes to suit. - Grandad

Grandad, does this mean that after the tank has expanded once from this process, it stays that way, and that this is not something that occurs on a regular basis as thermal expansion would, for example? Meaning that when I reinstall my 25 year old tank, it has already gone through it's hydrocarbon saturation (or something) expansion and I don't have to worry about it busting through the floor?

 

[Grandad]

Re: Plastic Gas Tank

Grandad, does this mean that after the tank has expanded once from this process, it stays that way, and that this is not something that occurs on a regular basis as thermal expansion would, for example? Meaning that when I reinstall my 25 year old tank, it has already gone through it's hydrocarbon saturation (or something) expansion and I don't have to worry about it busting through the floor?

Sorry, I really don't know much about it, other than Moeller's direction which doesn't explain much. My logic would be that you're always going to have fuel in the tank, so it'll never "dry out" and shrink again, but I dunno. I tried to attach a copy of the instructions in PFD format last night, but the attachment didn't stick. I'll try again now. OK, I see the problem; the file is 16 kB too large. I'll try pasting the website link below. - Grandad

www.moellermarine.com/.../moellermarine/.../ft1510br-1_7-27-12.p...

 

[Grandad]

Re: Plastic Gas Tank

OK. I found a smaller PDF. See instructions mentioning "hydrocarbon swell". If your tank has had fuel in it for 25 years, I doubt it's going to swell any further. See attachment. - Grandad

 

[oops!]

Re: Plastic Gas Tank

hi... welcome to iboats...

looks like grand dad has you in the right direction....

i just wanted to say welcome to iboats........ AND I LOVE THAT AVATAR.......lol

cheers
oops

 

[Ogden2]

Re: Plastic Gas Tank

Wow, great information Grandad. Thanks for the help, I never would have found that in time!

And thanks Oops!

 

[CaptainKickback]

Re: Plastic Gas Tank

oops! Great to hear from you. Haven't seen many posts from you lately.

Ogden2, I bought a 116 gal poly tank for my project boat. I haven't installed it yet, but where I bought it, they told me just don't foam the area or block the sides from expanding. They said just block it tight at the corners.

I don't know the chemistry, but what everyone has said sounds plausible. I had assumed the expansion was due to the weight of the fuel. Maybe its both.

Sea ya...

 

[Ogden2]

Re: Plastic Gas Tank

Thanks again! Also I noticed in the manual at the link that Grandad sent, they require the use of neoprene strips in holding the tank, but I also noticed that Frisco used strips of rubber from recycled tires. I wonder how those worked because I have the same method in use and I'm just about to glue them down. Maybe I should ask him...