Overpressurized Fuel When Filling?

[Rmahmood]

Hi Everyone,

I’m looking for a little help here. I just bought my first tow boat - 2010 RZ2. I fueled her up before trailering to the lake. All was going well, fueling smoothly with no issues. When full the fuel lever automatically stopped and then about 2 seconds later a ton of fuel sprayed out of the filler hole and drenched me. Somehow it got overpressurized. Outside temperature was in the low 70’s.

My question: How can I keep that from happening again and at the same time fully fill my fuel tank?

The only info I’ve found online says I should never fill my tank completely but how much less should I fill it? 10%, 25%...??% On the other hand when reading about winterization, I see that I should fill the tank as high as possible when adding stabilizer so I have less chance of condensation buildup.

How should I balance the different filling applications?

Thanks in advance!

[BCRider]

This is a classic issue when filling up the boat. Best practice if at all possible is to try and park bow down. Some also say to turn the nozzle upside down. I don't do that but I don't stick it in all the way and I listen as you can usually hear it when it starts to back up. Stop fueling every couple minutes to help let the air escape the tank. Open both filler caps as well. No one gets out scott free without drenching their arm at least once.

[boonecragun]

Do you have dual fuel caps? If so open both when fueling. Other than that ditto^.

[mikemcclain8]

I agree with listening as I fill the tank and stop as the pitch rises to avoid the overfill.

[SONIC]

Also near the end of the fill change to the slowest setting on the pump handle lock.

[Jetdriver]

I agree with the above. Best practice is to open both caps to better vent and take your time fueling while listening for the fuel coming up the tube.
You already learned this lesson the hard way but don’t stand in front of the nozzle either!
I don’t let others fuel it because they will spill gas every time. I’ve owned my boat 5 years and unfortunately still get caught sleeping every now and then.

[boatwakes]

Your vent is clogged. I own a fuel dock and we see this all the time. Trace the vent line from the tank and look for a kink in the hose. There is usually a loop near the overboard thru-hull vent and sometimes, if the hose is looped under the vent instead of over it, fuel will collect in the bottom of the loop and block venting air flow.

[KoolAid]

Do you have dual fuel caps? If so open both when fueling. Other than that ditto^.

Just FYI for everyone on the newer stuff with dual fuel fills (2016+ from what I recall). Both fill hoses have one way valve on them so the opening both sides does not help them like the older ones do. Thank the EPA on this one.

I'm with boatwakes, most of the time the issue is a kinked/blocked vent hose or the bow is just way too high.

[D&P Powell]

No one gets out scott free without drenching their arm at least once.

FACT!

[Rmahmood]

Ok, thanks everyone! I did not open the other fuel cap so I’ll try that as well as all other “go slow and listen” tips.

Ill also trace the vent hose to make sure it is positioned correctly and not kinked, clogged or damaged.

I appreciate all the tips

[Skroboskim]

I just walk away and pretend like it isn't going to happen, then act as surprised as the guy at the pump next to me. I'd be more careful if i filled up on the water, but my old boat did the same thing.

[sandm]

2 tige's and 1 supra all did the same thing for me if you run the automatic fill on the fuel nozzle.
learned to always man the fill lever and listen for it filling up. a couple extra minutes gassing up to prevent it from spewing all over the boat, trailer or yourself is time well spent in my book.

[IDBoating]

Agree with all the advice above, except turning the nozzle upside down. That actually increases the chances of this happening because the turn-off sensor in the nozzle expects it to be oriented in the "normal" way. Many nozzles have an illustration warning you NOT to invert the nozzle for exactly this reason.

It helps to think about how your tank is arranged. It's in the keel with the fill hose(s) at the back of the tank. This is why BCRider suggested parking "bow down". If the bow is high - which is how most trailers hold the hull - the front of the tank is the highest point which creates a trapped airspace. Fuel is heavier than air, and air is a compressible medium, so as you pour in the fuel its weight compresses any air trapped up there. If you can park bow-down that airspace moves to the back, with the fill hose(s), and can escape instead of being pressurized. The more level, or more bow-high, your tank is, the less this problem will affect you.

No matter what other things you do (opening the cap on the other side, making certain the vent hose is clear, listening for the sound to change) the fundamental problem is trapped air. If you fill at full speed the whole time, the air often cannot escape past the incoming fuel. Thus when the auto-shutoff turns off the flow (or there's a "lucky" disruption in the fuel flow), the trapped air all comes rushing out and causes the big burp you're experiencing. You can safely fill the first half(ish) of the tank at full speed, but as the tank nears full you need to ease off the nozzle and slow down the fill rate. This will give the air time to gracefully escape and leave cross-sectional area in the fill hose for it to do so.

I don't know where fuel tank vents are connected to today's fuel tanks, but I've often thought they really need TWO: One at the front and one at the rear, so no matter where the air pocket occurs it always has a way out that doesn't involve spraying the human.

[flyboy]

FACT!

Fact! I wrap a towel around the pump!