Fuel Tank Venting Problem ... Still

[Tulsah]

To recapp:

- boat is 2013 RZ2, of which I am the second owner.
- original owner has claimed that fuel tank venting was never an issue in the 32 hours he used the boat.
- the fuel tank generally fills fine.
- the problem presents as the boat sits on my driveway, cover on and in the summer heat.
- occasionally, fuel erupts from the vent assembly and runs down the side of the boat - approx 1/4 to 1/2 gallon can come out.

I began by checking the function of the original fuel/air separator and found it to be non-functioning. I ordered a replacement, installed it and found that the problem persisted. Following advice from this forum, I went for the big guns and installed the Racor LG100, which is at least 20x larger than the stock unit. Everything appeared to be working until this week when our temps started to climb. Same old problem has come back.

I spent last night completely disassembling the vent line and the Racor all the way back to the fuel tank. I blew through the lines, section by section, reassembled and blew through the whole system. It is not blocked.

What I'm finding that has me completely baffled is that the fuel tank is building and holding pressure from expanding fuel. I assume that when the pressure builds enough, it is causing the eruption through the vent. What I can't figure is how the tank is pressurizing given that it has a free, unrestricted path to atmosphere through the vent line.

Check out the video that I made today - may have to jack up volume a bit. I can open the fill cap every couple of hours and get this kind of pressure build up. Thoughts?

[Stingreye]

To recapp:

- boat is 2013 RZ2, of which I am the second owner.
- original owner has claimed that fuel tank venting was never an issue in the 32 hours he used the boat.
- the fuel tank generally fills fine.
- the problem presents as the boat sits on my driveway, cover on and in the summer heat.
- occasionally, fuel erupts from the vent assembly and runs down the side of the boat - approx 1/4 to 1/2 gallon can come out.

I began by checking the function of the original fuel/air separator and found it to be non-functioning. I ordered a replacement, installed it and found that the problem persisted. Following advice from this forum, I went for the big guns and installed the Racor LG100, which is at least 20x larger than the stock unit. Everything appeared to be working until this week when our temps started to climb. Same old problem has come back.

I spent last night completely disassembling the vent line and the Racor all the way back to the fuel tank. I blew through the lines, section by section, reassembled and blew through the whole system. It is not blocked.

What I'm finding that has me completely baffled is that the fuel tank is building and holding pressure from expanding fuel. I assume that when the pressure builds enough, it is causing the eruption through the vent. What I can't figure is how the tank is pressurizing given that it has a free, unrestricted path to atmosphere through the vent line.

Check out the video that I made today - may have to jack up volume a bit. I can open the fill cap every couple of hours and get this kind of pressure build up. Thoughts?

The LG100:
http://www.parker.com/portal/site/PA...ry=productline

"The Fuel/Air Separator captures fuel normally discharged due to agitation and thermal expansion up to 2.4 PSI."

So the vent will allow for some pressure to build up it sounds like. I remember reading that when I bought mine. I have not had any thermal expansion out the vent since. Ironically I filled it up to the top to see if it would expand enough to overflow out the vent and it did not..... on my boat it came out the fill cap as my fill cap is not a 100% air tight seal. I am not sure if thats normal or not (there is no gasket maybe I am missing a gasket).

Basically, I will not fill up my tank all the way if I am not using it that day and it won't be a problem. Hope thats helpful.

[mnpracing]

one other thing to check if you haven't, is to make sure the vent hose does not have a low spot in it. The lowest point should be where it connects to the top of the tank, and should rise all the way to the thru-hull vent opening. Also, if the boat is sitting so that the vent opening at the top of the tank is submersed, the only way the tank will be able to vent is to push that fuel out the vent tube. Sort of like if your ballast bag vent line is lower than the air pocket in the ballast bag, there's no way for the air to vent unless the water covering the vent port is pushed out.

[Tulsah]

Thanks for the replies. In my situation, the boat is sitting nose low in the driveway, which places the vent connection at the highest spot in the tank, and above the level of fuel. At the time I took the video, the tank is just shy of 1/2 full. The routing of the vent hose is such that it is a continuous rise from the tank to the vent thru hull - no low spots in between.

As for the LG100, I interpret their description to mean that it keeps the tank vented to atmosphere for air/vapor situations, but seals off in the presence of escaping fuel, holding it back up to a pressure of 2.4psi. This should be the way an F/A separator works.

I suppose it's possible that when surfing and heavily loaded, fuel is pushed into the vent line, and is held there by vacuum. This could later be pushed out by the steadily rising tank pressure. Again, if the line is open to atmosphere under normal conditions, it shouldn't be able to hold fuel by vacuum. I'm at a loss ...

[Stingreye]

As for the LG100, I interpret their description to mean that it keeps the tank vented to atmosphere for air/vapor situations, but seals off in the presence of escaping fuel, holding it back up to a pressure of 2.4psi. This should be the way an F/A separator works.

I think you are right, it should let air out and keep fuel in up to 2.4psi. It really doesn't make sense that your tank is building up pressure. If you remove the racor and put in a straight fitting, it would at least to you if you have a faulty LG100. I can see why you would be frustrated.

When you fill the tank can you hear air escaping out the vent line? When I upgraded to Racor LG100 I could audibly hear a difference in the venting vs the stock one (although mine is much older 2004).

[Ewok]

Does it only happen with the cover on? Is the cover blocking the vent?

[Tulsah]

Ok, so here's what I've found ...

When I blow on a line directly into the 90deg tank fitting for the vent, it takes a fair bit of pressure to overcome the "seal" or tank back pressure. Interestingly, when I do this, I can hear the gurgling of gas in the tank, as if the fitting were internally tubed lower into the tank??? Also, when I do this, the tank holds pressure and does not relieve until I remove the cap.

So, on to my next theory. Is it possible that the vent is actually connected to the gas tank in the wrong location? Could this particular port (of the three) be intended for the fuel return line rather than the vent? The picture below shows the arrangement of my lines. From top to bottom, they are presently configured as VENT, RETURN, ENGINE. Can anyone with a newer model with the PCM 343 confirm how their fuel line connections are arranged? All help and advice is greatly appreciated.

[mnpracing]

Can you disconnect the fitting for the vent line on the tank and confirm if there is a tube that goes down into the tank? If so, and if the second one down doesn't have that, you've found the problem. Thanks for doing the research on this.

[Tulsah]

Can you disconnect the fitting for the vent line on the tank and confirm if there is a tube that goes down into the tank? If so, and if the second one down doesn't have that, you've found the problem. Thanks for doing the research on this.

I had the fitting off earlier and there is indeed an internal fitting/structure of sorts that goes into the tank - it is definitely not just open to the highest part of the tank. Further, it appears that this internal fitting is molded right into the tank, so I'm not able to investigate it beyond that. I may need to spin off the other two and see if one of them is open to the top only. In speaking with a mechanic friend, he seems to think that the only one of the three lines that may handle or even require some amount of back pressure is the fuel supply line. In his opinion, the vent and return lines should be open to atmosphere.

[mnpracing]

Fuel Tank Venting Problem ... Still

So I just check mine and they are plumbed the same as yours on my 2013. I also blew on the vent from the outside of the boat and noticed two things: first pressure built up and when I stopped blowing the air came back out the vent. Then I took of the gas cap and blew on the vent again. When I did this air came out the gas fill opening. I only have about 3/4 tank of gas so I'll check it again when I have more gas, just in case there's an internal tube in the vent connection that only goes a little ways into the tank. Hope this helps. Maybe they changed the internal configuration between years.

[Tulsah]

So I just check mine and they are plumbed the same as yours on my 2013. I also blew on the vent from the outside of the boat and noticed two things: first pressure built up and when I stopped blowing the air came back out the vent. Then I took of the gas cap and blew on the vent again. When I did this air came out the gas fill opening. I only have about 3/4 tank of gas so I'll check it again when I have more gas, just in case there's an internal tube in the vent connection that only goes a little ways into the tank. Hope this helps. Maybe they changed the internal configuration between years.

Mine's a 2013 as well. It sounds like your is working as I would expect it to. When you blew into the vent line was there any amount of pressure to overcome? Thanks.

[mnpracing]

There didn't appear to be. Just felt like blowing in to a ballon where there was some resistance. When I let up, it seemed to make sense to me because the air came back out the vent. I didn't hear any gurgling like you did either.

I verified that your tank is the same as mine too (same TIGE part number based on your pic above). The manufacturer model # is FX4870IV (I think I have the last two digits correct, they were slightly rubbed off). THere's a number to the left of this model # on the blue sticker which is 3019645.

[Tulsah]

Thanks for all the help. None of the online material I'm able to find suggests that a vent line should be internally tubed to below the surface of the gas, which it appears mine is. Very curious...

[mnpracing]

Thanks for all the help. None of the online material I'm able to find suggests that a vent line should be internally tubed to below the surface of the gas, which it appears mine is. Very curious...

Best bet at this point is to take off the return line port to see if it's at the top of the tank, like you mentioned above. If it's not, I'd push to have the whole tank replaced under warranty, as that isn't how that vent port should be configured.

[Tulsah]

Mystery solved! One detail that I forgot to mention in my original post was that my boat normally sits in my driveway during the summer season ... bow low.

It turns out that the port on the tank where the vent is connected is indeed internally tubed - to the top of the front of the gas tank. This way, when the boat is level and full of fuel, the vent would be above the fuel level. This is most definitely so when the boat is on the water and typically bow high. Under normal operating conditions, a vent without this tube and connected to the rearmost part of the tank would not be open to atmosphere as it would be under the level of the fuel.

I tested the theory by moving the boat to the street, at which point, there is no more gurgling when I blow into the line. Further, a friend with a Z1 shone a bright light into the tank and can clearly see the tube heading to the front of the tank.

Thanks to everyone for all of the input and help!