Saturday, September 30, 2023


Fuel nozzle shuts off before RV’s gas tank is full, but never at Buc-ee’s. Why?

Dear Dave,
In the nearly 20 years we have owned our RV and during countless trips around North America, we have had trouble filling our gas tank. It will get about 3/4 full and the pump clicks off. Even if we reset the pump we cannot add any more gas. If we drive across the street to another gas station we can complete the fill-up. This problem never happens at Buc-ee’s, but is a frequent issue in California. This may not happen for several fill-ups then it will occur. What gives? —Sherry, 2005 Jamboree GT Class C

Dear Sherry,
Your Jamboree Class C is most likely running on a Ford E-450 chassis and has either a 30-gallon or 55-gallon gasoline tank. Gasoline comes from the underground tanks at the fuel station, through a pump typically at the base of the fuel pump, through the hose and to the nozzle. The nozzle has an automatic shutoff device call the Venturi tube to prevent overfilling the vehicle fuel tank and spraying gasoline out the fill neck.

According to Wikipedia, the Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of a pipe. The Venturi effect is named after its discoverer, the 18th-century Italian physicist Giovanni Battista Venturi.

The Venturi nozzle or pipe is the small square inside the fill tube and is actually a tube with the square cap at the end. As the fuel tank fills, vapors build up as well and go out the vent tube. Typically the handle is designed for the Venturi to shut off the air pressure that holds the nozzle handle open when it is submerged in rising gas. However, for many years I have found that even vapor pressure will shut it off, not just the liquid gas.

“Petroleum Transfer Engineer”

Part of your problem could be the pressure of the pump and splash back you are getting when it is close to the fill top. This could also be caused by the shorter length of your fuel pipe to the tank. Shorter fill pipes allow the nozzle to go closer to the tank and higher flow rates would splash the Venturi too soon.

Throughout high school and college I worked at a Standard Oil full service gas station when we actually pumped gas at 58 cents per gallon. A “Petroleum Transfer Engineer” sounded way more impressive than a “gas pump monkey”. We checked the oil levels and belts, and washed the windows. We did not vacuum out the floorboard, but the local Phillips 66 station did. Remember that? After college I even co-owned a small gas station called State Street Standard. We lost money for two years before I decided to go work at Winnebago Industries.

We had three pumps in the full service island and two in the self-serve. One pump had so much pressure that you could not open the handle fully as it would shut off almost immediately. With some cars, you couldn’t even use the hold bar and had to barely squeeze the trigger. We tried not to use that one if possible. Finally a Standard Oil technician came and swapped out the handle. What we found was that pump was new and had a much higher pressure flow that the older handles could not tolerate.

It is very possible that the pumps at Buc-ee’s either have a lower pressure pump or handles calibrated for the pressure and typically they are newer locations and would have new equipment. It could also be your vent tube in the tank and fill neck is restricted and a faster fuel flow creates more vapor faster. I would suggest verifying there is not a kink or pinch in the vent tube. Some are visible from underneath looking up at the fuel fill.

Maybe it is the handle

I spoke with a local fuel supplier who stated fuel handles are only good for about three years. There is a date stamped somewhere on the handle. The nozzles on the older handles get beat up pretty bad and can even become out of round and even bent. This creates an uneven flow and can cause splashing if the bottom near the Venturi is bent up! He suggested turning the nozzle upside down to place the Venturi higher and away from the splash at the bent area.

There is no government regulation on when a nozzle is to be replaced, that I know of. So this makes sense as Buc-ee’s typically are newer locations. Notice how this one looks a little worn and has uneven thickness of the nozzle opening. And California uses a rubber boot around the nozzle, which would restrict the vent from dispersing vapor pressure.

Could it be the type of gas?

It could also be the type of gas you are putting in the tank. There are so many different gasoline blends to choose from today and sometimes it is hard to tell what you are getting.

You know that the E85 has at least 70% ethanol and E15 has up to 15% ethanol. But in some cases, you do not know what the others have even though they are color-coded white, blue, and red. The three on the right are OK to use in any vehicle. However, the E85 and E15 can only be used in vehicles that are designed for the higher ethanol blend.

The white with an octane rating of 87 is typically blended with ethanol at 10%, which is E10 and advertised as Super Unleaded. Some fueling stations still carry unleaded gas without ethanol, which is the blue 91 octane and the red 93 that is called Top Tier gas. From what I have found in my seminars in the past few years, in California there are very few fueling stations that carry any gasoline that does not have some ethanol blend.

Why does that matter?

Like everything else, gasoline companies are finding every means possible to make more money, which means less-expensive refining procedures, fewer additives, and more blends. In high school I worked at a Standard Oil gas station and attended a training seminar that spoke of the 17 different additives that made our gasoline better than the new up-and-coming Casey’s gas. With cheaper refining methods, fewer additives, and ethanol, today’s gasoline can have several issues. One is burning hotter and not designed for smaller engines unless it is 100% unleaded with no ethanol. Another is fuel economy. Another big issue is expanding vapors with heat.

Gasoline vapors expanding

I remember in the late 1980s we had horrible vapor locking issues with the Chevrolet P30 Chassis, as the cheaper quality and ethanol would expand and clog the charcoal canister of the venting system. Owners would remove the gas cap and gas would spray out all over the place!

I believe that is what is happening in your situation, i.e., the gasoline vapors expanding and maybe a combination of a vent line slightly restricted.

Here is some data you need to collect.

  • Are you setting the lever on the handle at the full open position?
  • Have you tried using a lower setting when this happens?
  • What is the ambient temperature outside when this happens?
  • Does this happen after you have been driving while the tanks may be hot, or right when starting out?
  • What grade fuel are you using?
  • Have you tried 100% unleaded with no ethanol?
  • Other than Buc-ee’s is there any other brand that doesn’t have this issue?

The gasoline comes from cold underground storage tanks and then hits the hot metal of the fuel tank and the vapor expansion starts. I have purchased a lot of fuel at Buc-ee’s locations throughout Texas and almost all have no alcohol blends. But I know that no alcohol is harder to find in California. I would assume when you have an issue at one station and go to another across the street it is either a different fuel grade or your tank has cooled down and the vent is less restricted. Keep in mind, I have no actual data on the vapors, just thinking out loud!

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Dave Solberg
Dave Solberg
Dave Solberg is a leading expert in the RV industry and author of the “RV Handbook” as well as the Managing Editor of the RV Repair Club. He has been in the RV Industry since 1983 and conducts over 15 seminars at RV shows throughout the country.


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Mitzi Agnew Giles and Ed Giles
1 month ago

Thank you for fully explaining the problem, the possible causes and solutions.

Gary W Mayberry
1 month ago

Valve lubrication was the reason for the lead additive. After the removal of the lead, the engine manufacturers had to make the engine valves of hardened composition to cushion their operation. Yea, doesn’t make sense to charge more for less, but look at diesel fuel, less refining than gasoline, but more money.

William Anderson
1 month ago

Actually, the lead additive was added to gas to increase the octane rating. The lubrication of the valves was a secondary benefit. it was the valve seats that were hardened and is now a standard feature.

The reason that diesel fuel is so expensive has nothing to do with the refining and everything to do with global fuel markets. With the introduction of ultra low sulfur diesel in 2006, our fuel met the European emission standards and could be exported to Europe. Suddenly, US drivers were competing in a market where European drivers pay 4 to 5 times the cost in the US. Market economics 101.

Lawrence Neely
1 month ago

Ah, yes. back in the days when people came in and asked for $2 of gas and it would last them for a couple of days (and no such thing as self serve).

1 month ago

Top Tier Detergent Gasoline is a performance specification that is trademarked. It has nothing to do with octane rating – – Costco sells only Top Tier Gasoline and Diesel.

Bob M
1 month ago

E15 ethanol gas can be used in most new cars, but there is a drastic cut in gas milage. Check your owners manual first. I just read where the Dodge Hellcat engine was designed to run best for performance on E15 ethanol gas. Which surprised me. Non ethanol gas isn’t as common to get in Pa. It’s always high test and used mostly in small engines like mowers and Chainsaws. I’ve noticed Sheetz stations are carrying it as their replacing the gas station stores.

Neal Davis
1 month ago

Thank you, Dave. I just use much lower pressure on the handle for a few seconds after the diesel pump at the truckstop has automatically shut-off. I figure it gives me several additional yards (feet?) before the fuel is gone (8 mpg with a Cummins 450-hp 8.9 liter ISL engine) 😉

Stephen Snure
1 month ago

I’ve run into this problem frequently with both my 2011 American Tradition class-A motorhome and our 2017 Jeep Grand Cherokee. Like the fuel supplier Dave referenced above, when this happens I turn the nozzle upside down. In every case thus far the fuel filled successfully. The downside of course is that I have to hold the nozzle the entire time it’s filling.

Another note about filling the motorhome’s fuel tank. I have a ScanGauge-D digital gauge installed that tells me how many gallons of fuel have been used. To limit splash back and the nozzle tripping before the tank is full, I slow the fill rate ten gallons before reaching the full mark. FYI – I only fuel at truck stops that use high-flow nozzles.

John D.
1 month ago

I believe the tetraethyl lead was for valve lubrication and anti-knock purposes.

I remember that my grandfather always used unleaded premium Amoco “white gas” in his ‘55 Pontiac.

I also bought it for my ‘58 Studebaker – when I could afford it- even at 29.9 cents per gallon!

1 month ago

Good explanation Dave. I find using lower setting on fill ups is key to reducing the shut off, for all the reasons you mention. I find the last pic hilarious! The 87 octane without alcohol, shows a sticker they only except “local checks” for purchase?! How many places nowadays do that?! I don’t think I’ve ever paid with a check in my 72 young years! LOL!

Tommy Molnar
1 month ago
Reply to  Ran

This is funny about only taking checks from locals. In Quartzsite,one of the solar installing businesses there will only take checks from “OUT-OF-TOWNERS”. When I asked about that the owner said, “Have you seen the locals”?

Bob P
1 month ago

A very informative answer to a question. I’m a little older than you so my gas pump monkey time was when gas was 23.9 cents per gallon for regular and 27.9 cents for ethyl. There was no such thing as unleaded except in the form of Coleman lantern fuel. Lead was added for lubricant of the valves. That’s why I never understood when unleaded fuel came out it costs 5 cents more than regular to leave out lead they were adding to gas. I believe that was one of those marketing ploys, if we don’t have to add lead we can charge for not adding it to the gas. Lol

1 month ago
Reply to  Bob P

I thought the lead was for anti-knock purposes. Dave, what’s the reason for the lead?

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