gas tank vent - Maxum Boat Owners Club

jrogahn · 10-28-2018, 06:14 AM

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

mmwjr · 10-28-2018, 12:58 PM

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.

shrew · 10-29-2018, 02:28 PM

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.

mmwjr · 10-29-2018, 05:02 PM

Quote:

Originally Posted by shrew

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.

Pittguy · 03-30-2021, 10:31 PM

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.

mmwjr · 03-31-2021, 02:05 AM

Quote:

Originally Posted by Pittguy

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.

Pittguy · 03-31-2021, 02:55 AM

Thanks. Another thing to look into lol.

shrew · 03-31-2021, 03:52 PM

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.

Pittguy · 03-31-2021, 03:59 PM

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?

Pittguy · 04-03-2021, 06:43 PM

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.

mmwjr · 04-03-2021, 09:53 PM

The vent hose should have a loop the is higher than the vent.

Pittguy · 04-03-2021, 10:23 PM

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.

jparsons121 · 04-03-2021, 10:59 PM

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.

Pittguy · 04-03-2021, 11:29 PM

For sure safety is number one but the only place any leaks out is through vent on transom. Perplexing.

Phillbo · 04-03-2021, 11:34 PM

The fuel pump on the motor should NOT pressurize the tank.

mmwjr · 04-04-2021, 12:07 AM

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.

Pittguy · 04-04-2021, 12:55 AM

Not entirely sure. It is a Force 2 stroke 90 HP.

mmwjr · 04-04-2021, 01:30 AM

Quote:

Originally Posted by Pittguy

Not entirely sure. It is a Force 2 stroke 90 HP.

Not electric but manual pump and carbureted.

jparsons121 · 04-04-2021, 01:14 PM

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?

donald · 04-04-2021, 02:31 PM

Leaking fuel tank!!
Just my 2c

Don