1989 Monaco gas tank acts full and it isn't

[artgamble711]

Hi,
I have a 1989 Monaco. I usually put gas in the tanks by 5 gallon tank. (to save the $1.65 a gallon difference in fuel cost from local pump to on water price)

My port tank was reading less than 1/4 tank....and I believ4ee that is about correct. I added 10 gallons. I always add the same amount to each side.

I then went to add more and it started coming out the over flow vent. I am pretty sure the tank is not full. My starboard side is showing about 1/2 a tank.

I went for a ride for about an hour. Came back to dock and tried to add gas to port tank.

It took about 2 gallons and then goes out overflow again. The gauge shows less than 1/4 full. I think that is correct.

What could it be? I know it could be the gage or sending unit. But I always put the same amount of fuel on each side. I really don't think one side is full.

Thanks

Art

[goodday]

Hi Art, it sure sounds like your sending float unit is off, prob. not floating anymore, hard to say what's in tank with pump gas ? good luck

[WBO Admin]

With counter rotating engines the reversed one will always burn a little more than the other. Could that be the culprit?

[artgamble711]

Hi Art, it sure sounds like your sending float unit is off, prob. not floating anymore, hard to say what's in tank with pump gas ? good luck

That is what I am hoping for, I just don't think it is possible as I usually put in the same amount of gas in each tank. If I remember correctly, they are 60 gallon tanks each, and I think it should be way less than 1/2 full.

How do I check the sender unit?

Art

[artgamble711]

With counter rotating engines the reversed one will always burn a little more than the other. Could that be the culprit?

I have mercruiser 260's. I might be wrong, but I don't think one of the counter rotates.

Thanks

Art

[WBO Admin]

If you have two, one should rotate the other way

[cliffdweller]

Art, I do not have dual tanks but had a similar problem on a 2000 22 walkaround. It has a 99 gallon tank and the gauge would say 1/2 full but the tank would only take a few gallons of gas and fuel would start running out of the overflow. The problem turned out to be the overflow line. It was too long from the factory, this is when the boat was new, and fuel collected in the low point of the hose. When fuel was added the tank the air has to get out and most of it goes out the overflow tube. Well if that has fuel in it bubbles out the overflow making you think the tank is full. The overflow hose was shortened and tied up so it did not have a low spot in it and have not had any problems since. You can check this by blowing out the overflow line with compressed air and then seeing if the tank will fill. If you do this make sure the cap on the gas tank is open so you do not pressurize your tank. Also do not use a vacuum and try to suck the gas out of the line. That could have very explosive side effects. Hope this helps.