1979 170 fuel tank replacement

[alandry100]

Had an unexpected day off due to my 3 year old having pinkeye. He is totally fine - just not able to go to daycare.
So I opened up the can of worms. Actually all things considered everything looks pretty good. A lot of slime on the top of the tank
but some of it looks great. The coffin is dry - there is one drain hole in the stern center. The coffin cover was a little squishy around the clear pie plate over the "fuel gauge"?. I am going to dry it out and see if it is rotten or just wet. If just wet I think if I over drill fill with MarineTex and drill new holes.

There was no foam, interesting wood shims, and fiberglass? padding under the strapping.

 Here are some pictures - I think I am going to use the marinesurvey.com method.













Any hints or advice on how to change out the fill and vent?

Also - what is the goo on the top of the tank? Is it some sort of petroleum precipitate, product of corrosion of the aluminum, or deterioration of the lines?

[kraw2]

The tank has been replaced at some time. Was it leaking? If not I would just clean it up and put it back together. Leave the cover out in the sun if you can and dig out around the pie plate and fill it with thickened epoxy.

I like the way they correctly placed the 2 hose clamps in different directions.

Does the fill and vent need replacing for any reason? If you do the fill line is sometimes a bear to replace. I would remove the fuel pickup anti siphon fitting and repace it with an anodized aluminum barb fitting.

[alandry100]

kraw - there are no leaks that I know of. The tank has not been used since 2005 when the engine was replaced. The new engine has been used on  a remote tank since then. I think the fill and vent need to be replaced. I hope it is not too tricky.
So you think the tank is not original? What makes you think that. I have the surface record for the boat and do not see any tank replacement - will have to look at it again.

[Capt. Bob]

kraw - there are no leaks that I know of. The tank has not been used since 2005 when the engine was replaced. The new engine has been used on  a remote tank since then. I think the fill and vent need to be replaced. I hope it is not too tricky.
So you think the tank is not original? What makes you think that. I have the surface record for the boat and do not see any tank replacement - will have to look at it again.

1. Use a little mineral spirits and clean the "Florida Marine Tank" label off. The build date will be in the left corner as it is shown in your photo. That will give you a good indication as to when that tank was placed in the hull. It's not always 100% for sure but still a fair indicator.

2. You have gone this far, it would be foolish not to pull the tank out completely and inspect.  Corrosion will most likely be under the straps on the side and bottom. Non use does nothing to stop the corrosion. The tank surface must remain dry to slow the inevitable down. Pin hole corrosion will be what you're looking for and I'd bet there is some on that tank.

Good luck.

[alandry100]

Bob - thanks - I am inclined to replace the tank regardless of what I find.
So you think the best thing to clean the goop is mineral spirits?

[seabob4]

Bob - thanks - I am inclined to replace the tank regardless of what I find.
So you think the best thing to clean the goop is mineral spirits?

I've seen that goop before, on an old Mako tank.  That was from foam being broken down to it's petroleum derived base materials.  I'd use paper toweling to get the majority of it off, than any solvent to remove the stubborn stuff.

Like Bob said, pitting type corrosion is what you are going to be looking for, especially in areas where water could have been trapped against the tank.  As it stands, the tanks looks top be a mess.  But pull it, get it cleaned up, and then you know what you are dealing with.  Also gives you the opportunity to clean out the tank compartment and get it set up right to either re-install the old tank, or receive a new one.

If there is any evidence of corrosion, ditch the old tank and replace with a poly tank of similar dimensions...

[Capt. Bob]

So you think the best thing to clean the goop is mineral spirits?

As Bob stated, most solvents will do. I prefer mineral spirits. I like to follow up with Simple Green but "odorless ms" will clean the tank coffin very well and is easier on my nose.

Before


After.


Build date on manufacturer sticker in lower right corner.


Hard to see but reads 11/90. This is the original tank in my 91 WAC.

[gran398]

That was nice work there CB.

A quick way to get that mung off alandry would be a pressure washer, then the solvent, if you decide to reinstall. I'm with the other guys, check the tank build date. A bad or potentially bad tank is dangerous.

[alandry100]

If I decided to keep it I would get it pressure tested - which I imagine would cost $100 at least, if it checked out I would want to get it steam cleaned? which would cost at least $100. Seems like replacement for ~ $300 is the right option. I am really less concerned about replacing the tank than the fill and vent lines.

What should I do with the tank?

[gran398]

Again...what is the tank build date?

If it isn't over say 12 years old, it is most likely worth keeping. If it looks okay...clean it up and pressure test. You can do this yourself with a bicycle pump or a 12V air pump  (save the money).  Plug off the outlets, pump it to 4 psi and see if it holds pressure for 24 hours. That's it. Only 4 psi.

You don't have to pay to have it steam-cleaned either.  If you decide to keep it, it can be cleaned with Varsol.  Good news..the decent drainage/airflow in your tank coffin. Your tank may well be salvageable.

The hoses come later, and are secondary.  Sometimes they can be a bit contrary.  Never seen one that has whupped us yet.

No worries. Get that tank cleaned up and post back.

[alandry100]

Cleaned off the label - build date May 1978. My guess is that it is shot - but no smell of gas and I can't find any holes. I plan to replace but ... I will clean and pressure test out of curiosity. It's a long winter.

[gran398]

Good deal, you have the build date.

The tank is 34 years old.

Don't even bother with a pressure test. It's toast. Rip it out, take measurements, and plan on a new tank.

Nothing lasts forever, and in the case of a questionable gas tank...be concerned for the safety of your fam and crew. A new custom aluminum tank at 9 bucks per gallon on the fab is money well spent.

Any more than 9 bucks per gallon for an aluminum tank locally...you have quality options elsewhere....even with shipping.

A fave tank supplier to our membership is located in NJ.

Will save some bucks on shipping to you...fairly close.

You previously asked about the old tank disposal. Any scrap metal yard will be happy to make money on your delivered aluminum.

[kraw2]

When you get a new tank have them coat it with coal tar epoxy. That will protect it if water does ever get to it. You can use the 4lb. density 2 part foam to set the tank and fill in the sides. Trim the foam off flush with the top of the tank and use epoxy resin and fiberglass tape or cloth and it will give you a watertight installation.

[alandry100]

Pulled the tank today - will post pictures - cleaning out the coffin. Will post pictures of the tank tomorrow, much of it was good, but there were some really bad spots though I don't think there were holes.

I am inclined to use the, no foam/plastic runners 5200'ed to the bottom of the coffin method.

I like the idea of a drain just in case water gets in there somehow. It seems that the tank held up ok without foam, if there weren't pieces of carpet under the tank holding water it may have held up better.

[Blue Agave]

Agreed!  Go the no foam route.