Fuel tank venting

[Rhinohio]

Hello folks, boating season is right around the corner and I can hardly wait. Wanted to pick the brains of you more experienced mariners.

I have a 2006 Suntracker Party Barge with the fuel tank mounted in the transom as with most modern outboards. I want to replace the gas cap and got thinking about the vent screw on the cap that currently exists. My thought is to purchase a non-vented cap and add a thru hull vent that you would find on a below deck mounted tank. This would do two significant things. First and foremost it would eliminate the possibility of water being forced into the vent screw as the water pours over the tank while under power. I've watched the transom while at speed and I'm surprised this design has not been addressed by the boat manufacturers... the spray is serious. A bonus would be that it is no longer necessary to manually open the vent on the gas cap. I've made that exercise part of my launching ritual but have forgotten it on occasion. The plan is to add a tee at the pickup tube, extend a hose up the railing and mount the thru hull vent to some sort of bracket. Am I way off base here or does this sound like a reasonable solution for a potential water in gas problem?

I searched the internet for information but did not come up with anything. Specifically, I was trying to understand the workings of the vented gas cap. Is it some sort of check valve or is it simply opened and closed (my boat is in the barn at my property so I can't look at it)? I just can't get my head around how that could work. When I open the screw on a warm day, it vents vapor pressure out which tells me water can get in while the water rushes over the fill port. Or does it close until a low pressure builds in the tank and then opens to allow air to fill the tank and then suck water in with it? Here is the cap on my tank.



Sorry for the windy post but I'm trying to prepare for a uneventful summer if you know what I mean. It was really frustrating solving the water/fuel issues last year and want to do everything possible to prevent that in the future. Thanks to all in advance.

Mike

[brumbyvet.1044]

I'm not sure I understand your current setup but if the tank is in the motor pod, like mine is, you need a non vented cap. There should already be a vent hose running from the tank up to a thru hull vent. If yours is a built in tank, I would always recommend a non vented cap and a vent hose with proper thru hull. Vented caps are for portable tanks.

[Bryden24shp]

Mine was vented through the cap, originally, what a pain to fill the tank. The gas pump always cut off, gas burped all over the place. I got more gas on me than in my tank, sometimes. I bought a vent kit through Overtons and installed it. It works great. I also built a filler funnel that screws into the cap. The tank fills real easy now, no burping or sloshing. With 2 different lengths of PVC, I can fill it up easy on the dock, or from inside the boat. Was easy to install. Works fantastic. Just like my EzFenders, get an idea, tweak it untill it works....And it does....
Bryan

[Rhinohio]

So maybe I'm not crazy or anal or whatever you want to call it.

Yes, the tank is in the motor pod but there is no vent hose attached to the tank. There is the filler tube, the pickup tube and the sending unit. The fuel line exits the pickup tube and goes thru the primer bulb, thru the fuel/water seperator and to the motor. Venting for fueling is thru the large opening of the filler tube. Would it be possible to see a pic of your setup? If I had to guess, I would say none of this stuff has been modified but maybe it has... that might explain the excessive water in the tank I had to deal with when I first got the boat. Thanks to all.

Mike

[GregF]

When you say pickup tube, do you mean the fuel line to the motor?
You can't vent there. The motor won't work

[Rhinohio]

Yep, no other fittings on the tank. But now that you mention it, that don't make any sense. Now I'm really confused. I have a drawing of the fuel tank from Moeller that I will dig up... maybe that will help. Thanks.

Mike

[GregF]

You are either going to be adapting a vent hose to the cap or you are drilling another hole in the tank. The plate where the sending unit is mounted may be the best spot. Then you can do it far from the tank.
Hot shavings and gasoline don't mix.
If you drilled a 5/8" hole you could put a 1/4" NPT close nipple in there with nuts washers and a rubber washer to seal it up. Then screw a female NPT to hose barb on top.

[IMHB]

Mike...I think your WAY OFF BASE...You said...
"The plan is to add a tee at the pickup tube, extend a hose up the railing and mount the thru hull vent to some sort of bracket. Am I way off base here or does this sound like a reasonable solution for a potential water in gas problem?"

Here is why...if you put a T in at the fuel pickup tube then your motor will suck AIR.....that won't work..you need to vent the tank some other way....Maybe by drilling out the vent in the cap, and install a brass fitting that you can slip a 3/8" or 1/2" I.D.hose over, then run the hose to an overboard fitting. Be sure you make a high spot in the vent hose so water can't run from the vent outlet back into your fuel tank.

Good Luck to you...
Harry

[GregF]

This problem will go away by July. All new boat fuel systems are required to meet a similar standard to what a car has now.
Built in tanks will have a carbon canister venting system and portable tanks need a new style cap with a smart vent.

http://www.boatus.com/magazine/2012/feb ... hanges.asp

[Rhinohio]

I was at BPS over the weekend and looked at the fuel tank configuration of the new boats in the showroom. The tanks do in fact have an addition fitting in the tank and the vent hose runs up the transom and disappears. I was a little perplexed but they probably have a canister buried under the sundeck and then vented out to the outside.

Now that I have my head out of my ass (thanks GregF), I'm going to do the same thing. I planned on replacing the gasket under the sending unit, so with out of the way, I can "fish" a bulkhead fitting thru the opening. Something lie this:



I'll run the hose thru the opening for the battery cables and attach it to something like this:



I thought about screwing a hose barb into the filler neck but not sure if the wall is thick enough to get sufficient threads for a good seal.

[haganjeff]

Hey Rhinohio. Did you ever get this fixed? I have the exact same issue on my 2006 Bass Buggy 18 with a 60HP Bigfoot. The fuel cap is a simple screw top vent. I unscrewed it partially yesterday and it gushed out air for several minutes. The pressure build up is pretty extreme with it closed and sitting in the sun.

I am afraid to run the boat at speeds when the screw is open or vented because of the exteme amount of water spray that covers the transom during speed. There is a serious design flaw in how the water is dispersed. Water is constantly spraying the cowl cover and transom under speeds. Does this trimmed up or down.

I guess no harm, no foul if I remember to unscrew the cap everytime I get back to the marina. Thanks for your input.