Is my tank pressurized?

[Robert16star]

Today was my first on-water test since I rebuilt my fuel pump. I started with a full tank of gas that I had added a pint of oil to just to be sure I was getting oil from my auxiliary oil tank. I had made a mark on the oil tank and sure enough I did use oil during the day.

I ran most of the time at WOT and all was good until I switched tanks.

About 15 minutes after switching to my second tank (also full, but without oil) (half at slower speeds, half at WOT) the engine sut down. I squeezed the ball and it was soft / empty. I opened the tank for a moment, re-closed it tight, squeezed the ball till it was hard and the engine started and ran. I ran for a few minutes and the engine shut down again. After this I ran the rest of the way in with the tank cap on but not as tight as I usually do and I made it all the way in (both at WOT and at lower speeds) without and problems.

Questions:
1. Should I leave my tank cap something less then max tight while running?

2. Could I have a problem with the seal on the tank cap and need to look at replacing it?

Thanks for you time,
Robert

 

[iwombat]

Re: Is my tank pressurized?

If you're using portable tanks, your fill cap should have a vent in it - sort of a cap within a cap. That vent needs to be open or you'll get a vacuum in the tank preventing the fuel pump from doing it's job. Whatever volume of gas goes out, needs to be replaced by the same volume of air at atmospheric pressure.

 

[Robert16star]

Re: Is my tank pressurized?

After this I ran the rest of the way in with the tank cap on but not as tight as I usually do and I made it all the way in (both at WOT and at lower speeds) without and problems.


Sorry............this should have read "without any problems"

 

[iwombat]

Re: Is my tank pressurized?

Find where your tank vents and use that instead. It's a bit safer than a loose fill cap.

 

[Robert16star]

Re: Is my tank pressurized?

If you're using portable tanks, your fill cap should have a vent in it - sort of a cap within a cap. That vent needs to be open or you'll get a vacuum in the tank preventing the fuel pump from doing it's job. Whatever volume of gas goes out, needs to be replaced by the same volume of air at atmospheric pressure.

Thanks.........I tried to attach a photo of my tank and it's caps. Unlike the older tanks that I had a merc years ago there is no screw like vent on these tanks?

 

[F_R]

Re: Is my tank pressurized?

Many OMC tanks have automatic vents. Are there two little pins that get pushed in when you plug the fuel connector to the tank? One of those is the vent, and is automatic. While on the subject, do yiou see any fuel leaking out that area? If so, you are sucking air and need new o-rings in the fuel connector and/or the little pins.

 

[iwombat]

Re: Is my tank pressurized?

Good call. I had an image of a plastic tank in my head.

What kind of tank are we talking about?

 

[Robert16star]

Re: Is my tank pressurized?

You guys are great...........thanks for all the replies!


They are plastic portable tanks made by Dura-Tank.

Imported_F_R...........I do see the pins you are talking about, and no I do not see any fuel leaking out. In fact if I let the tanks sit in the sun (uncovered) the tanks will start to build pressure and buldge. When I unscrew the cap the pressure is released. The building of pressure happens with and without the fuel line attached.

I'm going to try and attach photos......

Thanks,
Robert

 

[F_R]

Re: Is my tank pressurized?

I'm not familiar with that tank.

 

[iwombat]

Re: Is my tank pressurized?

I'm not either, but it appears there is not a separate pressure vent. Maybe a loose cap is the intended way to vent.

 

[F_R]

Re: Is my tank pressurized?

Many newer tanks have a one-way vent that lets air in but not pressure out. That prevents spewing fuel out the vent. Well, I said "newer" but actually that goes way back into the '60s or '70s.

 

[samo_ott]

Re: Is my tank pressurized?

FR, the 60's and 70's are NEW for you!