Strange fuel tank issue
09-26-2013, 06:58 AM
#11
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Could fuel be sloshing around and thrown out the vent
while underway? No other way out
while underway? No other way out
10-15-2013, 11:20 AM
#12
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I agree with can't push more fuel to the motor. The only way that could happen is if the FPR diaphram is ruptured and sucking fuel back up to the intake plenum. But then, I would assume, the motor would run sh**ty or not at all. Have never experienced that data point so I don't know. So the only way it is getting out of the tank is the fuel fill cap or the fuel tank vent. And since the fuel cap is sealed with an "O" ring, it has to be the fuel vent; unless someone installed a "mystery" line between the tanks and that does not seem possible since the tank loosing fuel is not dumping it into the other tank. If you ever find out the cause, please post what it was!
Ed
Ed
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10-15-2013, 12:05 PM
#14
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Was the boat out of your sight at any time between the "top off, run, top off again" test? Maybe someone is stealing gas and that side is easiest to get to?
I see you didn't use the Sonic factory fuel valves, however are you sure that is the only part of the system? Not sure exactly how it works but it seems there may be a crossover line involved somewhere.
My boat always uses more fuel starboard, but I know it is because that engine does work slightly harder, and is usually opposite with boats that spin out. However, your situation is just unexplainable with your tests. Has to be a link somewhere.
If you were losing 15 gallons out the vent in the short time that you burned 30 gallons, you would know. A gallon of gas on the water looks like a tanker spilled.
I see you didn't use the Sonic factory fuel valves, however are you sure that is the only part of the system? Not sure exactly how it works but it seems there may be a crossover line involved somewhere.
My boat always uses more fuel starboard, but I know it is because that engine does work slightly harder, and is usually opposite with boats that spin out. However, your situation is just unexplainable with your tests. Has to be a link somewhere.
If you were losing 15 gallons out the vent in the short time that you burned 30 gallons, you would know. A gallon of gas on the water looks like a tanker spilled.
10-16-2013, 09:48 AM
#15
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Granted I just got my 358 but my Port side uses a fair amount more (according to the guage) than my Starboard side.
Mine is full factory stock 496 HO's but I filled it up a few times and I would say the tanks are about 1/8th tank off from one another when pumping the same amount of fuel into both.
Mine is full factory stock 496 HO's but I filled it up a few times and I would say the tanks are about 1/8th tank off from one another when pumping the same amount of fuel into both.
10-17-2013, 06:02 AM
#16
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Thanks for all the replies and ideas. But so far I've not been able to figure it out. It's still happening and driving my crazy. BTW once the problem is solved the boat is going to be for sale
10-18-2013, 11:28 AM
#17
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Have you had to put more fuel in 1 tank vs the other since you bought the boat? Could it be that 1 tank is larger than the other? ...thus not really burning more, but takes more to fill to top?
10-18-2013, 08:46 PM
#18
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He is either leaking gas, or he is linked and has uneven equalization. I think the tanks are equalized with a hose.
A friend has a trip engine boat with center engine drawing on both tanks and tanks equalized, doesn't work. He always draws more from one tank.
10-18-2013, 10:28 PM
#19
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I have a sonic 35ss, 725's super charged, bravos. The boat has 2 70 gal aluminum tanks which were replaced in 1997. I have only owned the boat for 2 years and bought it as a complete project.
The port side tank uses much more fuel than the starboard . Each engine runs independent on its own tank. There is no fuel valves or crossover that I can see. In fact it is a very simple fuel system . 1/2" line with AN fittings straight from tank to mech fuel pump then to fuel filter and then to carb. Port tank drains 1/3 faster than other.
Here is a list of the tests I have done so far:
Filled both tanks to the top, ran the boat then topped both tanks again, results 45 gal used port . 30 gal used startboard.
I did that test several times with always the save results.
Next I swapped the fuel lines so the port engine now draws from the starboard tank. The problem does not follow the engine it stays with the port tank. Again I filled both tanks to the top, ran the boat for a while and topped the tanks both off again . Port tank took 1/3 more fuel .
There is NO smell of gas at any time and my bilge has no signs of fuel.
Any ideas??????
The port side tank uses much more fuel than the starboard . Each engine runs independent on its own tank. There is no fuel valves or crossover that I can see. In fact it is a very simple fuel system . 1/2" line with AN fittings straight from tank to mech fuel pump then to fuel filter and then to carb. Port tank drains 1/3 faster than other.
Here is a list of the tests I have done so far:
Filled both tanks to the top, ran the boat then topped both tanks again, results 45 gal used port . 30 gal used startboard.
I did that test several times with always the save results.
Next I swapped the fuel lines so the port engine now draws from the starboard tank. The problem does not follow the engine it stays with the port tank. Again I filled both tanks to the top, ran the boat for a while and topped the tanks both off again . Port tank took 1/3 more fuel .
There is NO smell of gas at any time and my bilge has no signs of fuel.
Any ideas??????
10-19-2013, 07:41 AM
#20
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Any pictures of the setup?
It would seem there has to be an equalizer or some sort between the tanks. With that much horsepower, I assume you removed the anti-siphon check valves from the fuel tanks or are they still in place?
With everything you have already done, that's the only other thing I can think of. Perhaps one of the check valves is stronger than the other so you are pulling 66% of the fuel from the weaker sprung valve, and 33% from the other.
It would seem there has to be an equalizer or some sort between the tanks. With that much horsepower, I assume you removed the anti-siphon check valves from the fuel tanks or are they still in place?
With everything you have already done, that's the only other thing I can think of. Perhaps one of the check valves is stronger than the other so you are pulling 66% of the fuel from the weaker sprung valve, and 33% from the other.
