Expanding Gas and/or Air? or What?

[tperk100]

I have a 50 gal metal tank. Right or wrong, for winter storage I filled the tank ALL THE WAY UP to the top of the fill tube with treated gas. Then I ran the engine for a few minutes and observed the fuel level going down in the fill tube.

A week of so later (on a relatively warmer day) the gas was overflowing out of the fill tube. I attributed this to warm weather expansion, so I siphoned FIVE GALLONS of fuel out of the tank.

Problem solved....so I thought. Yesterday (a warmer day also) the fuel was overflowing again! Now I have already taken over 10 % of the fuel out of the tank. Could it possibly be expanding this much? I doubt it.

Friends have tried to convince me I have a venting problem. The tank appears to be vented through the fill tube cap. Here is a link to the Perko cap. You can see it has a connection for the vent. So, if here is any venting of gas, it seems its supposed to discharge through the cap and run all over the boat rub rail as it has been doing. (destroying the rub rail to hull sealant)

http://pdf.nauticexpo.com/pdf/perko/marinium/21871-2826-_6.html

I can see that the actual vent tube is attached as it seems to be intended.

Can anyone shed any light on this? Will gas expand this much? Any other thoughts / suggestions?

Thanks much.

 

[rodbolt]

Re: Expanding Gas and/or Air? or What?

yep, thats why you dont want to top it all the way when its cold.
fuel can expand quite a bit.

 

[tperk100]

Re: Expanding Gas and/or Air? or What?

Since my post I have done a little research and learned that gas does not expand anywhere near 10%......so.....I still do not know how to explain what is happening.

 

[trendsetter240]

Re: Expanding Gas and/or Air? or What?

Since my post I have done a little research and learned that gas does not expand anywhere near 10%......so.....I still do not know how to explain what is happening.

What did you put in the gas as a treatment? Also is it possible that water is getting into the tank and that is what is causing the fuel level to increase?

 

[tperk100]

Re: Expanding Gas and/or Air? or What?

I have Yamaha Ring Free and StarBrite StarTron in the gas at maintenance levels, not shock levels.

I also thought about water getting in the tank, since both overflows were after rainy periods. But the engine runs fine, and the boat has a new custom Sunbrella cover that fits like a glove. I doubt that water is getting into the tank.

 

[tperk100]

Re: Expanding Gas and/or Air? or What?

OK Guys...since you could not tell me what was going on, I will tell you!!

Today, the fill tube was overflowing again. This is after siphoning off AT LEAST 10% of the gas out of the tank. Gas DOES NOT EXPAND TO 10%....so why am I still overflowing???

Answer....vent tube is blocked. Tank cannot get atmospheric relief. How do I know this?

First, I removed the gas cap (Note the configuration of this cap . Click above link for info)

Then I disconnected the VENT hose from the tank, and then listened to a large WHOOSH, as air rushed into the tank. Obviously the vent was obstructed. Now get this...I want to know exactly what's happening. Sooo..I gently blow into the vent hose I disconnected from the tank. I hear gas bubbling in the line. I blow just a LITTLE bit harder and blow all the gas out of the line. I could find no other debris. Then I hook my compressor to the line and blow it out with 100 psi....no other debris or obstructions observed

I am perplexed. Why was it VERY easy for me to blow through the vent hose? The hose was definitely obstructed as evidenced by the rush of air into the tank when I disconnected it.

Maybe a vent hose should be installed such that it NEVER drops below the gas tank level....so that no gas could ever stand in the hose. Do you think that gas in the hose might have "gelled" or some other weird b/s?

All I know for sure is that the vent was blocked. I have hooked it all back up and will monitor to see what develops.

 

[BTMCB]

Re: Expanding Gas and/or Air? or What?

Question asked, answered, explained, solved by the same poster. Brilliant. And thanks for a heads up!

 

[180shabah]

Re: Expanding Gas and/or Air? or What?

You are correct, your vent line should run continuously UP from the tank to the vet, with no dips. It should also, include a loop that is higher than the vent, to prevent iphoning water back into the tank.

 

[backwater dawg]

Re: Expanding Gas and/or Air? or What?

Still sounds fishyyyyyyyy

 

[smokeonthewater]

Re: Expanding Gas and/or Air? or What?

yes yes and yes
next you caused this dragon to rear his hear by over filling your tank such that gas entered the vent hose.... the routing of the hose prevented the gas from running back into the tank

 

[tperk100]

Re: Expanding Gas and/or Air? or What?

Kevin,

When I disconnected the hose at the tank, the WHOOSH was very loud. It seems that such a negative pressure would have easily sucked the gas from the hose back into the tank.

We'll see what happens.

 

[smokeonthewater]

Re: Expanding Gas and/or Air? or What?

was it negative? should have been positive.... that said it would not suck all the gas out even if it did have enough vacuum..... Instead it would pull air bubbles through..... Try to blow all the water out of a loop of garden hose with your breath.... Trying to lift a thin liquid with a air is fighting physics unless the hose is to small to allow mixing or the velocity of the air is greater than the liquid can fall through it..... That's why the air compressor was able to blow it out

 

[tperk100]

Re: Expanding Gas and/or Air? or What?

I think you are right about the direction of the air. I do think it was coming out as opposed to going in. Matter of fact, it had to be that way because the air was forcing the fuel up to the top of the fill tube!

But see where I said I blew gently on the vent hose and I was able to clear it. I don't know why the gas tank air could not have done the same thing. I only used the compressor to really blow the line out with force, but it was already cleared at that point.

This is all very interesting. The air in the gas tank was able to push tank fuel up to and out of the fill tube......but not the vent tube???? That tube had to have been clogged with something...... besides just a little gas. We will see how it works now.

 

[smokeonthewater]

Re: Expanding Gas and/or Air? or What?

sometimes a vent is designed to retain slight pressure but allow intake of air to prevent a vacuum..... if your fill cap wasn't sealing as it obviously was not then the path of least resistance would be out the cap.... on all my boats the fill caps have been air tight

 

[smokeonthewater]

Re: Expanding Gas and/or Air? or What?

Or is your vent maybe higher than your fill?

 

[tperk100]

Re: Expanding Gas and/or Air? or What?

My fill tube and vent lines are integrated into one assembly. The fuel is SUPPOSED to leak out of the cap when necessary.

Here is that assembly.

http://pdf.nauticexpo.com/pdf/perko/marinium/21871-2826-_6.html

 

[Home Cookin']

Re: Expanding Gas and/or Air? or What?

You can drive yourself crazy when the stuff you know doesn't add up, but the real problem is something you don't know. Here's my suspicion: something temporarily blocked the bottom of the vent tube. maybe there is a flap over it designed to keep fuel from rising. More likely some debris floated up to the bottom of the vent and lodged there until your efforts dislodged it enough to get an air path through (major culprit these days in fuel path failure is a piece of the foil seal in the tops of oil, stabilizer, etc.)
Still a 10% expansion is odd. If the boat is on a lift or trailer, the angle may have been off for good venting. Plus our unusual 3 weeks of cold weather may have done unusual things. POst this on Tidalfish and see what comes up.

PS how do you like the 19' scout? My sister is shopping for something similar. Would yo be OK with a 115 on it?

 

[Tacklewasher]

Re: Expanding Gas and/or Air? or What?

I've been pouring gas in his tank at night.

 

[BTMCB]

Re: Expanding Gas and/or Air? or What?

I've been pouring gas in his tank at night.

I am STILL laughing! Good one.

 

[tperk100]

Re: Expanding Gas and/or Air? or What?

Home Cookin..what you are saying about the possible foil blockage makes perfect sense..at least to me.

We'll see what the future holds for the "mystery" vent / expanding problem.

Could you other guys put some diesel in my truck too?