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How many additional miles do you think you get with the splash guard gone?
SPLASH GUARD??? I got a laugh out of that terminology! It is (well, was) a splash creator. lol. But, I agree. It's removal rational is not for getting more miles per tank, but to avoid the splash of gas with some fast delivery pumps. I insert the pump's nozzle to the bottom of the black filler neck's down tube and let the pump self kick off.

prs
 
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For the OP, the "leak" is due to the expansion and probably accented by leaving the bike on the jiffy stand. AND, yes, your charcoal can is probably saturated and would likely benefit if you stopped flooding it.

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And this is why I regularly urge posters to be precise (no pun intended) in their language and use correct technical terminology, especially when it comes to diagnosing bike issues.

DanPrecision, your bike is not “leaking.” gasoline. As others have pointed out, if you “overfill” your gas tank (up to the brim of the filler opening, for example), then park your bike on a very hot day with a hot engine (especially on the sidestand), the gas will expand slightly due to heat and run out through an OVERFLOW TUBE.

It’s happened to me on my ‘19 DCT Tour and on previous bikes, like my ‘14 BMW R1200RT.

This overflow is simply the result fuel expansion. IT IS NOT A “leak”, as others have pointed out.

Don’t worry about it. Don’t fill to the top of gas tank’s opening on a hot day if you’re going to park immediately afterwards.

Tim
 

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GL1800 Doctor
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From what I’ve seen, there’s no overflow hose. There’s a spill hose that routes anything spilled around the outside of the filler neck to the ground and there’s a drain hose on the evap canister that will drip liquid gas out of it if it gets sucked in. Just like the older 1800 wing, the gas tank should not be filled to the cap. There needs to be room for expansion so the evap system doesn’t suck liquid gas into the canister and ruin the charcoal.
 

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SPLASH GUARD??? I got a laugh out of that terminology! It is (well, was) a splash creator. lol.
I just used the OP's terminology. It is a bit easier to say than "white tube thingy", or "fill hole protector", or "filler neck tube".
 

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I don’t know if there is an overflow tube or not. Many (most?) motorcycles do.

The question of tubes (one of which might be for fuel overflow) has been discussed here previously. I found the thread, but couldn’t figure out how to make a link to it.

It’s labeled, “Tube hanging under 2018 DCT”. There are pics.

Fyi.

Tim
 

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A few months ago, I removed the white plastic splash guard (proper name?) from the filler opening on my 2018. It makes filling so much easier, but I have a tendency to now fill almost all the way to the bottom of the opening in order to get the most miles between fill ups.

On my recent day trips, I would fill up, then ride the bike away from the pump and into a parking space. I would go in to use the bathroom and when I came out, I would see a small wet patch of gas under the bike. It wasn't much...guessing about an ounce...and it never seemed to happen on the first fill up of the day.

Is the overflow happening because the entire bike (engine/tank/etc) is warm and the pressure increases slightly when the gas cap is replaced? Or could there be a problem with my charcoal cannister?

I'm sure I just need to take it easy with my fills and leave a bit more room. I just want to make sure there isn't another minor underlying issue.

There was a pervious thread, maybe more than one, regarding removing that white thing in the gas neck. Here's the bottom line.......................and it CANNOT be argued with any FACTS......... Honda put that thing in there for a reason. I have no clue why specifically, But, I can guess. Regardless of my guesses, yours and the man in the moon, it's there for a specific reason. Of THAT, there simply is no question. Sooooo........................ leave it alone. The end.

Not for nuttin'........................you're filling it to get more mileage out of that tankful ??? How much more mileage between fill-ups are you getting ?? MAYBE...............MAYBE an extra 2 miles ????

Put that thing back in there and don't touch it. Mr. Honda put it there for a reason. He knows WAAAY more than you and I and anyone else about his bike. WHO CARES what the reason is ??

# 2 1/2.
 

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leave a 1/2" for expansion

otherwise it can overflow

maybe fill up 30 miles sooner-big deal
 

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It more than likely the heat from the engine & sun is expanding the fuel in the tank while it sets there and some is coming out of the overflow tube like it is supposed to, that is why they do not want you to OVERFILL IT!! Thats why the tube is in there. Especially on the side stand!! Running down the road you use a little and the wind is keeping it cool. Fuel expands with heat as does oil. Contracts when cold, dats what my science teacher taught us!!!! lol...
I had tried to get the insert out but could not do it. I finally just stick the gas into tank and wait for it to shut off. I filled up when my gas light came on which means i have a gallon left. I filled up and it took 4.2 gallons instead of 4.5 when you fill to the top. Not worth a few extra miles in my opinion.
 

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Discussion Starter · #33 ·
I had tried to get the insert out but could not do it. I finally just stick the gas into tank and wait for it to shut off. I filled up when my gas light came on which means i have a gallon left. I filled up and it took 4.2 gallons instead of 4.5 when you fill to the top. Not worth a few extra miles in my opinion.
I appreciate everyone's opinions on the matter. I frequently run my tank down until the range reads ---, which is less than 10 miles on the tank. I usually can get 5.1 to 5.3 gallons in, without any of it coming out of the overflow tube (well, at least I never noticed it), which is a far cry from the 4.2 gallons that your getting in, @Wild Turkey. That actually could be an extra 40 or 50 miles.

I don't want to beat a dead horse, so I'll just leave it at that. Once again, thank you for all of your thoughts on the subject.
 

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GL1800 Doctor
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I don’t know if there is an overflow tube or not. Many (most?) motorcycles do.

The question of tubes (one of which might be for fuel overflow) has been discussed here previously. I found the thread, but couldn’t figure out how to make a link to it.

It’s labeled, “Tube hanging under 2018 DCT”. There are pics.

Fyi.

Tim
Yep, the first pic shows two hoses and the second picture shows the evap canister on the left with one of those two hoses connected to it. One of those hoses is a fresh air vent hose for the canister and the other one is the drain that empties any liquid fuel that’s gotten sucked into it. The only other hose is for the spill tray around the top of the tank for accidental spills. If the tank actually had an overflow hose, it couldn’t pass the emissions requirements because the hose would leak fuel vapor from the tank even when it’s not overly full. The 18-19 service manual shows all three hoses and where they are attached.
 
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