Fuel Tank Bubbles?

I got home from my evening commute and was hearing some gurgling inside the tank. Looking inside, I could see air bubbles rising thru the fuel, apparently coming from the secondary tank. There's no fuel running onto the floor, but if air is coming in, fuel has to be going somewhere; I'm guessing into the secondary. I've heard it gurgle before, but it's rare. This is happening on a 20-30 second interval.

By way of information, it's a 2006 with 98,600+ miles. I put about 250-300 miles a week on it.

Also, in a maybe related bit of info: for the past few weeks, when the low fuel warning light comes on, it stays on for 10-20 miles or so, then the fuel gauge goes back up to 2 bars like it got more fuel. The range between fill-ups hasn't changed, and the MPG hasn't changed. I can only assume that something is going on in the hoses and/or valves between the tanks, or maybe the float is sticking. Maybe there are fish in there.

Thoughts?

I posted a vid of it on YouTube.
[video=youtube_share;0xW8h9HbIpU]http://youtu.be/0xW8h9HbIpU[/video]

I occasionally hear the same from my tank, even an hour or so after I've parked the bike (and topped it off with gas).

No ill effects from it.

No worries....There are quite a few previous threads on this subject....some very long and detailed....winter gasoline formulas still being used on warmer days....differences in volatility/state change to vapor, etc....and rising engine heat to help.....

Sounds like maybe that 'ol "gas boiling" issue (in name only)...no real boiling of course. Can occur on warmer days (like today) during winter/spring when stations are still serving up the winter blends of gasoline (more volatile) and haven't switched to summer formulas yet. You can actually see gas movement in the tank. There are multiple threads on it here.


First time I heard/saw it was after pulling into Pinnacles on 25 on a very warm early spring day. Lasted about 15 minutes just after parking the ST when hot.


This is assuming your vent tubes are clear too.


My 2 cents...

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Mine always does that too when the tank is near full and just parked engine hot on a warm day. I suspect it's normal.

Sometimes I hear this on my ST with no problems as it is just fuel returning to the tank from the fuel rack. Sounds like your fuel sending unit may be in need of replacement with the bars coming back on in the gauge.

Yup.. it's Fish!

I agree with all above, typical and some hear it and some don't. Some thought the gas was boiling but it's just the pressure in the system being released/equalized. Some will say their ST takes a long time to start after sitting for a bit because it takes a little for the system to re-fill/pressurize...

I agree w/Mike - you could have a stuck sending unit in the upper tank giving you false readings as it nears the bottom of the upper tank and before the lower tank's thermister takes over.

If it got to one bar or distance to empty then the thermistor got exposed to air iirc. Something in that circut. Not sure if it indicates high or low resistance. The service manual should help.

Besides the fish living in the tank, I'd say you have a kink/twist in the hose between the upper and lower tank. Air is coming up as the fuel drains down.

Also explains the low fuel indicator.

The main tank is not draining to the lower... you eventually use up enough fuel in the lower to where the thermistor is exposed, kicks and says your on the final gallon. Then... you hit a bump and the fish in the tank belch some air from the lower tank to the top, thermistor gets covered, you have gas.

Just a thought of mine...

T_C said:

Besides the fish living in the tank, I'd say you have a kink/twist in the hose between the upper and lower tank. Air is coming up as the fuel drains down.

Also explains the low fuel indicator.

The main tank is not draining to the lower... you eventually use up enough fuel in the lower to where the thermistor is exposed, kicks and says your on the final gallon. Then... you hit a bump and the fish in the tank belch some air from the lower tank to the top, thermistor gets covered, you have gas.

Just a thought of mine...

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Dude! that totally makes sense!

Mellow said:

Dude! that totally makes sense!

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When you say it that way... it kinda scares me... I might be right.


In reality... if you hear gurgling during fill up, no big deal. But if you hear and see gurgling after you stop the bike and it repeats, you have a problem between the two tanks. Fuel should normally flow smoothly between the two. But in your case... The lower tank isn't venting properly and it's using the large diameter fuel hose to feed both fuel to the lower tank and the air out of it. Your getting a form of vacuum lock, fuel won't go down because it won't let the air up.

T_C said:

When you say it that way... it kinda scares me... I might be right.


In reality... if you hear gurgling during fill up, no big deal. But if you hear and see gurgling after you stop the bike and it repeats, you have a problem between the two tanks. Fuel should normally flow smoothly between the two. But in your case... The lower tank isn't venting properly and it's using the large diameter fuel hose to feed both fuel to the lower tank and the air out of it. Your getting a form of vacuum lock, fuel won't go down because it won't let the air up.

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So... after a little over three years later from the last post of this thread... in remarkable 70+ degrees(F) February temps yesterday... after 30 mile ride on '03ST1300...topped up tank and rode home about 20 miles... very easy back road cruising... no heavy throttle... shut off bike & heard the "boiling"/"gurgle" even with ear plugs & helmet on!... took off helmet & removed ear plugs... pushed bike into garage... opened tank... heard gurgling & bubbles exactly as the YOU-TUBE video of the OP Thread Initiator... looked carefully about bike for any leakage evident... none!... sniffed about bike for gas odor... none!...EXACTLY as the video... after reading thread... it seems like the last post by T_C is most plausible explanation... now...IF the lower tank is not venting "PROPERLY"... for someone such as I of limited knowledge on this issue... please explain as a follow up to the above post what needs to be done(details, please) to alleviate this "FORMING OF A VACUUM FUEL LOCK"... thanks in advance for informing me(others) as to how to get the lower tank to again VENT properly...

Check the VENT line down at the bottom where it exits, sometimes critters build webs or nests and clog them up!
Now...how many members wanna tell him to STOP using the OEM key in the gas cap before it bends/breaks?

Igofar said:

Check the VENT line down at the bottom where it exits, sometimes critters build webs or nests and clog them up!
Now...how many members wanna tell him to STOP using the OEM key in the gas cap before it bends/breaks?

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Well, Igofar,...thanks for your quick reply...I can/will check on that VENT line "clogging" done by the critters... even I can handle that & since bike has been sitting in garage for over couple months... the garage critters may have ignored my attempt to form a defensive perimeter around bike!...FUNNY you would mention OEM key quip as I have had every intention... even today before posting... that I was going to get a replacement key cut soon... with your mind-reading prowess... perhaps you should go pick up a few "pick-five" lottery tickets!... Thanks again for what hopefully is an easy fix for me!:bow1:

silverbub said:

Well, Igofar,...thanks for your quick reply...I can/will check on that VENT line "clogging" done by the critters... even I can handle that & since bike has been sitting in garage for over couple months... the garage critters may have ignored my attempt to form a defensive perimeter around bike!...FUNNY you would mention OEM key quip as I have had every intention... even today before posting... that I was going to get a replacement key cut soon... with your mind-reading prowess... perhaps you should go pick up a few "pick-five" lottery tickets!... Thanks again for what hopefully is an easy fix for me!:bow1:

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I even had a similar thing happen on my Honda Element. Every time it rained I would get water on the passenger floor matt. They checked everything, sealing, windshield, firewall etc. Could not figure it out! I even ran a water hose over everything on the front of the car and engine to no avail, then I noticed that whenever I used my heater fan, water would pump into the car from under the dash ***?
Turns out the rain pooled in the smog canister, and spiders built webs and clogged the vent hose, and by using the fan, it pumped the standing water back up into the car.
I have helped a couple other Element owners with this issue. My tank gurgled once and I cleared mud/dirt/debris from the end of the hose and it stopped it.
Yes, some folks think it may be normal, and accept it, however....OCD don't roll like that

The solution seems pretty clear:

T_C said:

Besides the fish living in the tank, I'd say you have a kink/twist in the hose between the upper and lower tank. Air is coming up as the fuel drains down.

Also explains the low fuel indicator.

The main tank is not draining to the lower... you eventually use up enough fuel in the lower to where the thermistor is exposed, kicks and says your on the final gallon. Then... you hit a bump and the fish in the tank belch some air from the lower tank to the top, thermistor gets covered, you have gas.

Just a thought of mine...

Click to expand...

T.C., I think you just answered my big ST problem. After 200 miles I bounce between half a tank and 20 miles remaining. Then half a tank or 30 miles. Then half a tank and 45 miles remaining. I get fuel and have more than 1.5 gallons was still in tank.
I'm replacing that hose next, thank you..

Have this problem in the summer in Las Vegas, normal riding the rest of the year but in the 100+ heat the fuel tank gurgles for up to an hour after a ride., Will be checking the venting.

Igofar said:

Check the VENT line down at the bottom where it exits, sometimes critters build webs or nests and clog them up!
Now...how many members wanna tell him to STOP using the OEM key in the gas cap before it bends/breaks?

Click to expand...

Can you point me to a diagram, or explain where, this vent line is that I should check. It would be nice to not gurgle anymore!