OMC 6-Gal Fuel Tank Ventilation

[andrewi]

Could someone explain the ventilation system on these plastic fuel tanks. It seems that the cap has no screw-type valve to allow air to enter the tank when operating. However, the service manual refers to a Viton valve which allows air to enter the tank during operation. However, when the tank sits and/or pressure builds in the tank, there is no valve to allow the air inside to escape. Unless you leave the cap opened a bit pressure continues to build in the tank. In other words, how is preassure in the tank supposed to escape. Thanks, irao

 

[DJ]

Re: OMC 6-Gal Fuel Tank Ventilation

irao,<br /><br />The tank has to be vented. Something on your tank is either missing or clogged.

 

[Beaux]

Re: OMC 6-Gal Fuel Tank Ventilation

Is it the original cap? Every one I have seen has a vent screw that must be opened during use of motor. <br />IMO, you need to buy a new cap. The whole tank shown is only 24.99 so, the cap should not be $$$. Is this similar to yours?<br />

 

[andrewi]

Re: OMC 6-Gal Fuel Tank Ventilation

Beaux, No. My tank appears longer. Mainly, I can remember to open the cap when operating, but when the tank sits and gets heated without the cap loosened, the tank will become pressured. The cap does have a small cork looking small round piece in the middle inside of the cap, but doesn't seem to let the tank breath. Thanks, irao

 

[rickdb1boat]

Re: OMC 6-Gal Fuel Tank Ventilation

irao <br /><br />Just get yourself a new cap like the one shown on the tank in the picture. That will take care of your problem for under $10.00.

 

[clanton]

Re: OMC 6-Gal Fuel Tank Ventilation

The OMC metal tank is not vented until you connect the connector, dont know about the plastic tank.

 

[clanton]

Re: OMC 6-Gal Fuel Tank Ventilation

Found a book. 1 style of OMC metal tank had 2 pins on the tank connector, when you connector the connector it pushed the 2 pins in and vented the tank. The 2nd style OMC metal tank had a knob on the cap for vent. Looks like the OMC plastic tank has a one way check valve in the manifold on top of the tank.

 

[seahorse5]

Re: OMC 6-Gal Fuel Tank Ventilation

The plastic tank pictured above is not an OMC tank.<br /><br />The plastic OMC tank is vented for vacuum when a fuel fitting is connected to it. There is no venting for pressure so as not to fill a bilge with gas fumes possibly causing an explosive mixture. There is no vent in the cap. In the hot sun, the tank may "swell" a bit and that is normal and designed into the tank.

 

[andrewi]

Re: OMC 6-Gal Fuel Tank Ventilation

Seahorse, I appreciate your confirming what I had suspected, i.e., the one-way ventilation into the tank (but not out of the tank) is a safety feature designed into the tank to prevent explosive fumes from finding their way to the bilge area and possibly causing an explosion. The problem with this is that the pressure inside the tank causes "sloshed" gas to be forced out of a loose cap (without a gasket) or a loose connection on the fuel gage side of the tank. This problem effectively defeats the purpose for which the tank was designed. For my money, I will install a vented cap as my boat is an open 17 foot aluminum where gas fumes collecting would be only a minor problem, but something of which to be aware. Thanks, irao