ST1300 - Fuel Gurgle - Normal or Not

jfheath

John Heath
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Joined
Mar 18, 2006
Messages
3,175
Location
Ilkley, W Yorkshire, UK
Bike
2013 ST1300 A9
2025 Miles
002293
It has been a long winter and spring lay off - during which time I have had the fuel tank off, synchronised the starter valves, checked the 5 way tee and reassembled. New fuel joining hose and clamps.

I have had a few short rides since then and everything has felt fine - no - everything has felt brilliant. The engine purring beautifully and smoother than it has ever felt, even when new. But it has been sitting with the same fuel in the tank for some while. A few weeks ago I added some injector cleaner fluid and ran if until the fans came on. I had no stabiliser, and shops that sell that stuff are not open at present.

Today is hot by UK standards, and we went out for a legitimate run out to have a picnic, not to meet anyone, but to enjoy the scenery and fresh air. As lockdown is released we are allowed that now. Although there were large groups of bikers out - which is not allowed (We can meet up with just one person) Before we headed back home I filled up with fuel. To the bottom of the filler neck. It felt even better on the way back, fresh fuel and all - but that might have been just imagination.

Back at home, I put the bike in the garage, got my gear off and then went out to empty the panniers. The fuel tank sounds as though it has got indigestion, bubbling and gurgling at intervals. A couple of seconds at a time, every 20 - 30 seconds. I opened the fuel filler cap and with a flash light, I could see the disturbance at the side of the tank. The tank was still very full - up to the bar that goes across the filler neck. I was standing on the left of the bike and with a light, could see what I assumed to be bubbles / burps breaking the surface of the fuel on the right hand side of the tank. Bike is on its centre stand.

So air getting into the fuel, must mean fuel getting out - or air is expanding. But I can see no sign of escaping fluid. The lower/upper fuel joint is OK. There are no leaks around any of the lower tank joints.

One of the drain tubes which emerge at the rear of the sump, near the gear pedal is damp with fuel (not wet through, and not dripping), and I can see the air disturbed by vapours - so the tank is venting through that hose.

I've heard the engine and tank make odd noises, but never this tummy rumble type noise - but then - after about 120,000 miles and 13 years of ownership of 2 ST1300s I cannot say that I go into the garage after I have put it away hot. So its entirely possible that this is what it does, and I have just never heard it before. The air temperature gauge says 31 deg C - but it has been sitting in its own heat in a closed garage. Its not that hot outside - maybe 20-25.

Question is - do I need to go delving, or is this normal ? The noise is getting less and less as the engine cools down, and it is definitely coming from the tank and coincides when the bubbles can be seen through the filler cap.

edit - 20 minutes later, it has stopped doing it - but the question still remain as to whether or not this is normal.
 
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LIving in subtropical Florida if my ST1300 didn't make odd noises like that in hot weather I'd think something was wrong.
 
I get that from time to time and have no idea what why it happens. It's been mentioned a few times along with suppositions as to the cause. As the bike always starts and runs properly afterwards I don't give it another thought.
 
Fresh fuel has a higher vapor pressure. Also with fuel inventory being high you ma have gotten a winter blend which has even higher vapor pressure. I have experienced this phenomenon and believe it is the hot soaked engine boiling the fuel in the fuel rails on top of the engine. The boiled fuel bubbles return to the tank via the return line.
 
Thanks folks. Yes - @Tom Mac 04a - percolator just about describes the sound exactly.

I'd not heard of the different blends before, @CruSTy. But boiling fuel seems likely. It had to be heat related. Nice that @ST Gui can confirm exactly the same thing. It means I don't have to get the spanners out.

Most odd that after 13 years of owning a ST1300, it has decided to let me hear it burbling for the first time after filling it for the first time since having the two tanks separated !
 
LIving in subtropical western Florida my ST1300 makes odd noises all the time in hot weather.

Really, it does, scary at first but will sound like a 5 gallon pot of boiling water and continue for 15 minutes after a hot ride.
 
I have experienced this phenomenon and believe it is the hot soaked engine boiling the fuel in the fuel rails on top of the engine. The boiled fuel bubbles return to the tank via the return line.
Here in Canada, in the early spring, we experience a similar "fuel gurgling" phenomenon - it is caused by the frozen fuel thawing out and the large fuel iceberg in the tank breaking up into smaller bergy bits. :)

Michael
 
Ha. First time I heard this noise I was concerned.
However, here in Az it's a common event.
Does sound a little like a coffee percolator.
 
The lower/upper fuel joint is OK.

My 2003 made the same noise for a long time. I also lifted the main tank and checked the connector hose.

Hose looked fine when tank was up. However ... i kept an eye on it as I slowly lowered the tank. Turns out the hose bent (crimped, so partially collapsed) while in the down position.

I removed the hose and discovered it was not an OEM hose - obviously original went bad, so original owner replaced with a generic "flexible" hose, verses the OEM molded (bent) hose.

I'm sure my old post is out here somewhere, with photos : )

EDIT: My 2008 does not make the gurgling sound ... and the 2003, after I replaced with an OEM hose, never gurgled again. (and in our searing South Texas heat!)
 
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Thanks @Indian Express and @caldercay - I did take a good look at the newly fitted OEM joining hose and lifted the tank so that I could see both ends. That was perfectly fine.

"Over half a tank in hot weather" - that is a useful observation. It is unusual for me to have a full tank after a day's riding. That might explain why I have never heard it before.
 
My 2003 does the same since the last few years. I think it is the ethanol in the fuel that is boiling. ethanol has a much lower boiling point than gasoline.
Back in 2003 there was no ethanol in the fuels and it did not gurgle. These days, ethanol, gurgling and in my case even engine cutting out when the fuel gets hot (vapour in the injectors)...
 
Been using Shell 91 lately,,, for no ethanol. Although I wonder if still get a smidge out of the pump hose, from the previous guys fill. I have never noticed any fuel gurgles or boiling sounds with any fuel. In fact,, my tank does not really seem to get particularly hot. Being dark blue,, you would expect it to heat more than a silver tank,,, just from solar. But the source of heat from the engine, I expect would be a result of the lower tank being heated,, and then the hot fuel being circulated to the upper tank. Obviously,, the more fuel there is in the upper tank,, the larger the heat sink capacity,, and the less air space expansion will occur. I have seen on a number of bikes,, efforts to insulate,, and apply reflective coatings to the bottom of the tank. These were all single tank setups,, as far as I know. Just all food for thought,,, cheers,, and happy fathers day,, to all my fellow dad's !! CAt'
 
My 2003 made the same noise for a long time. I also lifted the main tank and checked the connector hose.

Hose looked fine when tank was up. However ... i kept an eye on it as I slowly lowered the tank. Turns out the hose bent (crimped, so partially collapsed) while in the down position.
This is a very common problem, even with the OEM hoses. The hose routing below the tank is complex, and there are two different specifications for hose routing (pre- and post 2007). It is very easy to unintentionally change the routing of the hoses so that one of them kinks when the tank is lowered.

Below is a picture of the hoses on my 2012 bike (incorrectly routed, I confess) and also an excerpt from the Service Manual showing the correct routing of these hoses. The text "this one was missing" refers to a clamp shown in the Service Manual illustration that was not present on my bike when I inspected it - compare the diagram with the photo above it, you will see where the clamp is missing.

Michael

Hoses under Fuel Tank
Fuel Tank Hoses.jpg

Hose Routing Diagram
Honda Hose Routing Diagram.jpg
 
Yep, thats what I saw too. Thanks for posting that. I don't think that the fuel that you can see in the tank is boiling. I think the disturbance is caused by hot fuel vapours being vented into the tank, and the bubbles disturb the fuel that you can see.
 
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