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Old 10-28-2018, 05:14 AM   #1
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Default gas tank vent

I just bought a 1988 1700 maxum boat with a built in 12 gallon gas tank. where do I vent the tank? or is it unnecessary
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Old 10-28-2018, 11:58 AM   #2
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Welcome aboard

A factory built in tank should already have a vent. There should be a small chrome thru hull vent on the side of the boat near the back. On my boat it’s about four feet from the transom.
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Old 10-29-2018, 01:28 PM   #3
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All marine fuel tanks are vented, regardless of whether they are onboard or portable. They are only necessary to fill the tank or draw fuel from it.
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Old 10-29-2018, 04:02 PM   #4
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All marine fuel tanks are vented, regardless of whether they are onboard or portable. They are only necessary to fill the tank or draw fuel from it.
In other words totally necessary to use the tank. When filling the vent allows air to escape as it is being displaced by fuel and just the opposite when operating the engine.
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Old 03-30-2021, 09:31 PM   #5
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Sorry to bring this one back up but as a new owner of 89 1700 XR I have a related question.

My gauge reads half or a little more. I have not added fuel but I did just run it the other day for a few moments with water muffs. Anyway, as I just noticed when the evening sun is on the boat I had some fuel come out of the vent on the transom. Enough to soak the cover a little and in the rocks below evidence it wasn't the first time.

Something to be concerned with? As expansion happens is this correct? I read about a loop should be there in the line to the vent? Is there more fuel than I could have know when I got this last week?

Thanks in advance for any thoughts.
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Old 03-31-2021, 01:05 AM   #6
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Quote:
Originally Posted by Pittguy View Post
Sorry to bring this one back up but as a new owner of 89 1700 XR I have a related question.

My gauge reads half or a little more. I have not added fuel but I did just run it the other day for a few moments with water muffs. Anyway, as I just noticed when the evening sun is on the boat I had some fuel come out of the vent on the transom. Enough to soak the cover a little and in the rocks below evidence it wasn't the first time.

Something to be concerned with? As expansion happens is this correct? I read about a loop should be there in the line to the vent? Is there more fuel than I could have know when I got this last week?

Thanks in advance for any thoughts.
With fuel coming out the vent from thermal expansion I would say the fuel tank is full and you sender is off giving a low reading.
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Old 03-31-2021, 01:55 AM   #7
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Thanks. Another thing to look into lol.
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Old 03-31-2021, 02:52 PM   #8
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You might want to try and drain some of the fuel out of the tank to prevent this from occurring. You can install a whistle on the vent line to prevent overfilling. When you're filling the whistle makes noise. When the noise stops.....stop filling.

Ideally, you only want to fill the tank to 90%, to leave room for thermal expansion.
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Old 03-31-2021, 02:59 PM   #9
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Thanks. I literally had no idea how much is in there when I bought it. Was just surprised as it happened some days after getting it home and checking it out. Warmer weather is my guess then. Also maybe I lean it too far back in the drive for rainwater flow off cover?
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Old 04-03-2021, 05:43 PM   #10
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So I went back to the boat today again after it having sat some more days. It is much cooler now also. Remove the cover which was dripping with fuel.

Got in and took off all covers etc. By sight the tank is not full. Don’t have any sort of thing to slip into the tank. All hoses are solid. I squeeze the vent hose and no fuel comes out of vent.

The vent hose is simply a straight rubber hose. I have read before there should be a loop? Or it should loop higher than something else?

At any rate still puzzled and concerned about this and what to try.
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Old 04-03-2021, 08:53 PM   #11
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The vent hose should have a loop the is higher than the vent.
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Old 04-03-2021, 09:23 PM   #12
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Ok I will have to get a longer hose. One more thing I did notice today though as I had a partner to see.

The fuel will come out if I turn the key to the on position to check electrical things but not turn over the motor. I guess the fuel pump pressurized and if the motor doesn’t burn it off it goes out there after a delay.
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Old 04-03-2021, 09:59 PM   #13
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Electric fuel pump will come on when key is turned to Run to build pressure. No fuel should escape overboard (or anywhere else) if the key is left in run without starting.

I’d highly recommend you look at your entire fuel system and find that leak before running the engine or even using anything that may spark.
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Old 04-03-2021, 10:29 PM   #14
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For sure safety is number one but the only place any leaks out is through vent on transom. Perplexing.
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Old 04-03-2021, 10:34 PM   #15
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The fuel pump on the motor should NOT pressurize the tank.
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Old 04-03-2021, 11:07 PM   #16
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The fuel pump should not cause fuel to come out the vent. Do you know you have an electric fuel pump? Is this a carbureted or fuel injected engine? If carbureted and it has an electric fuel pump it should not pump fuel until the engine is cranking as it gets power from the starter solenoid when starting then from an oil pressure switch once running.
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Old 04-03-2021, 11:55 PM   #17
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Not entirely sure. It is a Force 2 stroke 90 HP.
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Old 04-04-2021, 12:30 AM   #18
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Quote:
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Not entirely sure. It is a Force 2 stroke 90 HP.
Not electric but manual pump and carbureted.
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Old 04-04-2021, 12:14 PM   #19
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With it being an outboard, disregard my prior post on fuel pump.
As Mike And Phillbo mentioned, the tank shouldn’t get any pressure from anything on an outboard.

Going out on a limb here, but are you sure the fitting is the vent, not the thruhull for your bilge pump? I ask because of the last post where you stated you were doing electrical checks and it came out.
Can you post a picture?
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Old 04-04-2021, 01:31 PM   #20
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Leaking fuel tank!!
Just my 2c

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