Older metal Omc fuel tank question.

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Jmar
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Location: Chesterfield, Michigan

Older metal Omc fuel tank question.

Post by Jmar » 23 Jun 2016, 20:58

So my fuel tank leaks at the gasket when not in use after running and has some pressure in the tank, I just ordered a new gasket for it. My question is do I need to loosen the cap to relieve pressure every time I turn off the motor on the water? The tank is older, has no vent cap, and has the pins on the connector where from what I've read lets air in, but not out. I've forgotten a couple times now only to look back and notice fuel running down the tank. Even when I replace the gasket, that doesn't seem like that will fix the pressure issue. The fuel will just push up into the motor is what I'm thinking. I've searched all over for this and can't find a clear answer. Evinrude connectors. 1979 9.9hp. Thanks.
14ft 1960's Foremost w/ 1979 9.9 Evinrude

http://forum.tinboats.net/viewtopic.php?t=40332

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Johnny
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Older metal Omc fuel tank question.

Post by Johnny » 24 Jun 2016, 08:14

I am not an expert on this matter but I do have 3 or 4 of
these fine metal vintage tanks.
I have heard that when the cap gets rusted or lost, the
boater simply goes down to the auto store and buys a
radiator cap for it - - - - this does NOT work on these tanks.
The original cap has a relief valve in the cap - the radiator
cap does not. So first - check to see what kind of cap you have.
it should have a wire spring type keeper fastened to the cap, #14 & 15
then, come back with your findings.
cap.gif
cap.gif (4.44 KiB) Viewed 450 times
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1959 Crestliner Commodore 14'
1959 Lone Star Malibu 14'
1958 Johnson 35 RDE-19 Sea Horse
1958 Johnson 35 RDS-20 Super Sea Horse

Jmar
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Joined: 24 Mar 2016, 11:14
Location: Chesterfield, Michigan

Older metal Omc fuel tank question.

Post by Jmar » 24 Jun 2016, 08:25

This is the cap. Not sure if it is original. Has no way to relieve pressure.
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14ft 1960's Foremost w/ 1979 9.9 Evinrude

http://forum.tinboats.net/viewtopic.php?t=40332

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perchjerker
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Older metal Omc fuel tank question.

Post by perchjerker » 24 Jun 2016, 08:28

I would loosen the cap

you could ask on a vintage boat forum

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Johnny
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Older metal Omc fuel tank question.

Post by Johnny » 24 Jun 2016, 08:38

you have the correct cap.
the button on the cap is the pressure relief gizmo.

another really good site to visit is http://www.aomci.org/
the "Ask a Member" button can get you some very valuable information.
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http://www.tinboats.net/how-to-build-a-transom/
http://www.tinboats.net/varnish-vs-polyurethane/
All about Primers = http://www.tinboats.net/primer-and-paint-basics/
Paint, Thinners and Applications = http://www.paintingforpainters.com/

1959 Crestliner Commodore 14'
1959 Lone Star Malibu 14'
1958 Johnson 35 RDE-19 Sea Horse
1958 Johnson 35 RDS-20 Super Sea Horse

Jmar
Posts: 48
Joined: 24 Mar 2016, 11:14
Location: Chesterfield, Michigan

Older metal Omc fuel tank question.

Post by Jmar » 24 Jun 2016, 09:45

That little button on top of the cap does not pop up, twist, turn or seem to want to move at all. And there's no mechanism under it to make it pop. It just seems like a rivet that holds the locking mechanism for the cap in place. I looked on that other link you posted, but when I clicked on ask a member I keep getting an error on the website.
14ft 1960's Foremost w/ 1979 9.9 Evinrude

http://forum.tinboats.net/viewtopic.php?t=40332

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Johnny
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Older metal Omc fuel tank question.

Post by Johnny » 24 Jun 2016, 11:34

This is summer - the hottest days on record.
I would loosen the cap until you find out what is going on.

I posted your question on AOMCI and will wait for
someone to reply to your specific issue.
There was one response on how to completely
overhaul the old metal tanks - but, I don't know
if you want to get that involved in saving an old soldier.
http://www.oddjobmotors.com/tt4_singlelinetanks.htm
http://www.tinboats.net/how-to-build-a-transom/
http://www.tinboats.net/varnish-vs-polyurethane/
All about Primers = http://www.tinboats.net/primer-and-paint-basics/
Paint, Thinners and Applications = http://www.paintingforpainters.com/

1959 Crestliner Commodore 14'
1959 Lone Star Malibu 14'
1958 Johnson 35 RDE-19 Sea Horse
1958 Johnson 35 RDS-20 Super Sea Horse

Jmar
Posts: 48
Joined: 24 Mar 2016, 11:14
Location: Chesterfield, Michigan

Older metal Omc fuel tank question.

Post by Jmar » 24 Jun 2016, 12:21

Thank you. I also saw that online and when the gasket shows up and I replace it I will see if the leaking stops. If it does, I think I'll be good. Hopefully it'll vent correctly through the pin if not I'll have to check the O-rings.
14ft 1960's Foremost w/ 1979 9.9 Evinrude

http://forum.tinboats.net/viewtopic.php?t=40332

KMixson
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Older metal Omc fuel tank question.

Post by KMixson » 24 Jun 2016, 14:56

Johnny wrote:I have heard that when the cap gets rusted or lost, the
boater simply goes down to the auto store and buys a
radiator cap for it - - - - this does NOT work on these tanks.
The original cap has a relief valve in the cap - the radiator
cap does not.

A radiator cap does have a relief valve but it would not work in this situation unless you removed the uppermost gasket in the cap. You would also need to have a lip for the main seal to press against to allow pressure to build while under way. I do not see a lip in the picture that would let the main seal do its job. When pressure builds up in a radiator there is a spring that lets the bottom main seal of the cap relieve pressure through an overflow port on the radiator filler neck to your overflow tank. This happens while the upper gasket seals it from coming out of the lip around the cap. As the radiator cools off and a vacuum forms inside there is a little valve in the center of the cap that pulls coolant from your overflow back into the radiator keeping the radiator full at all times. If you just want to seal the whole can and not have a vent at all the radiator cap will do it if you get the right size cap. The only problem with that is that fuel will find the point of least resistance and exit that way. If your needle valves in your float bowl are leaking you will flood your motor. Myself, I would look at getting the correct part for the can if possible.

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Johnny
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Older metal Omc fuel tank question.

Post by Johnny » 24 Jun 2016, 15:24

Post by Chinewalker » AOMCI member
" Fact is, there is NO vent in the cap. The vent is in the fuel fitting on top of the tank. You'll see two pins sticking out of the fitting. One is a fuel valve, allowing fuel to exit the tank into your fuel hose. Other is an air vent that allows air into the tank as fuel leaves. There's a check valve that prevents air from escaping the tank. It is normal for them to pressurize a bit in the sun, warm day, etc. If all your hoses, fittings and carb bits are in good shape, it isn't an issue. If you're worried about pressure forcing fuel through the carb or whatnot, unplug the tank when not in use.
I prefer these tanks as they tend to allow less moisture into them, resulting in less water related fuel problems.
It is fairly easy and inexpensive to rebuild the fitting if needed. "
- Scott
http://www.tinboats.net/how-to-build-a-transom/
http://www.tinboats.net/varnish-vs-polyurethane/
All about Primers = http://www.tinboats.net/primer-and-paint-basics/
Paint, Thinners and Applications = http://www.paintingforpainters.com/

1959 Crestliner Commodore 14'
1959 Lone Star Malibu 14'
1958 Johnson 35 RDE-19 Sea Horse
1958 Johnson 35 RDS-20 Super Sea Horse

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