Massively Over-fueled 2010 Honda Odyssey: Where Did All the Gas Go?

There’s a story behind this one. I know the Car Talk community loves stories, so here goes. (Skip below if you don’t want the long-winded tale.)

I noticed our minivan was low on fuel when I pulled into our driveway this afternoon, so I figured I’d put some gas in the next time I drove. My wife drove next and, while she was out, filled the tank completely. Later that night after running an errand, I remembered I needed to put some gas in the car. Without bothering to check the fuel gauge (which, unbeknownst to me, now read full), I pulled into a local gas station and told the attendant to put in $20 of regular.

We live in Oregon, where you don’t pump your own gas, so I sat and listened to my local NPR station while waiting for the attendant to do his job. He was the only attendant working at the time, so he was servicing other cars in addition to mine. After what seemed like an inordinate amount of time, the attendant informed me that the gas pump kept “clicking off” and that he was only able to put in $10 (about 4 gallons at the current price). I told him no big deal, $10 was fine, and drove off towards home. At this point I noticed that the gauge read full, and I began to worry that I had unwittingly force-fed my van 4 more gallons of gas than it was capable of holding. The car also smelled noticeably of gasoline by the time I got home (less than a mile away).


Where did all that gas go? The tank only holds 21 gallons. No gas came back up out of the fuel filler neck (I think the attendant would have noticed that). So where did those 4 extra gallons wind up? I’ve never overfilled a tank before–I’ve always stopped fueling when I heard the click–so for a first time over-fueling, I’ve really outdone myself. (Though technically I should give partial credit to the attendant who actually put the gas in.)

Is there potential damage to the car? How can I get it checked out to make sure that it’s safe for my wife and kids to ride in again? Any insights would be very much appreciated.

Thanks in advance! Hope you enjoyed my tale of woe.

When your wife filled up, the attendant probably stopped the first time the pump clicked off. There may have been room for some more gas. The fill tube was probably empty and your wife drove home, you drove to the gas station using some gas. The second fill up took up every bit of excess space and likely filled the tube (from the gas cap to the tank) There is potential damage to the evap recovery system as liquid gas may have gone into the vapor recovery tubes. Older cars were easily damaged by overfilling, newer cars can still be damaged but are a little more forgiving. Drive the car to use up the gas to get it out of the fill tube and hope the evap system did not get messed up. You will get a check engine light if it does have liquid in it. If you are lucky it will clear itself, if not your local mechanic can fix this for you, $$.

If it makes you feel better, I managed to do the same thing once, except that I was the one filling it both times! (I was trying to get a huge list of things done in a hurry to get ready for a trip and somehow it slipped my mind that I already filled up earlier in the day.) I don’t remember how much I added, although I suspect it wasn’t quite this much. The gasoline smell went away after the level went down a bit and there was no permanent damage.

As already mentioned, if there is damage, you’ll get a check-engine light. I don’t think you need to get anything checked out otherwise. For safety reasons, you do need to be careful of where you park (not in a garage and not in the nearer part of the parking lot where the idiot litterbug smokers might throw their cigarette butts) until the gas smell goes away. It would be a good idea to take the car for a long drive now to get the level down and see if there are any issues.

Many gas pumps click off too early. Your situation reflects this. I’s impossible to add 4 gallons to a “full” fuel tank. Just keep driving and switch gas stations.

When refueling my F-150, I’ve noticed that the pump clicks off quite prematurely, and it’s entirely possible to get another 4-5 gallons in by simply continuing to manually pump in the remainder at a reduced rate. My Bronco had the same quirk. My Mustang doesn’t though, when the pump clicks off when refueling it, it’s basically full.

I agree with @Docnick the pump probably just clicked off a bit early. You don’t have anything to work about if this was the only time it’s happened.

From now on, listen and make sure the attendant stops at the first click. He may have forced some gas (not 4 gallons) into your evaporative emissions recovery system, not good for it.

It was technically illegal in Oregon for the attendant to add fuel after the click but I’m guessing they thought the nozzle was malfunctioning. I would also suggest driving it enough to burn 2 or 3 gallons. or syphon that amount into a proper container and return it to the van when the gauge reads 3/4 full or lower.

Drove it around a bunch this morning. No check engine light. Everything seems to be just fine, luckily!

This somewhat tangential to the subject, but what are these “attendant must pump” laws supposed to accomplish anyway?

Jobs is my only guess.

Jobs is right. Here in New Jersey the gasoline retailers association has lots of influence. We’re one of only two states where you can’t pump your own gas.

I expect everything fine OP. But what can happen in that situation is the gasoline saturates the evap canister with liquid gasoline. That dissolves the little beads of carbon or whatever’s in there. And this dissolved carbon can plug the ports of the evap canister and potentially clog the purge valve too. All that can make the computer think the evap system isn’t working, and trigger an evap code and turn on the check engine light. And in some situations this can eventually cause the engine to studder or stall. So be on the look-out, and if symptoms like that start to happen suspect the canister and purge valve.

And, of course, be very careful in the future to never fill the tank past that first “click”. Or let the gas station attendant do so.

I made the mistake a few years ago of getting gas at a station that had attendants, and, despite my standing there and repeating “don’t top off”, he still did.

@BillRussell You sometimes have to hit these guys over the head! My wife won’t tank her own gas, and I instructed here to only gas up at our Co-op station which has well trained staff.

The worst I have seen was gas jockey first filling the tank of a customer and then, to get an even number of dollars (so he would not have to make change) just dump the rest of the gas on the ground from the hose!!!

And the funny part is that most payments are via credit cards, so there is little change to be made.

It doesn’ actually dissolve anything, it just saturates the bed with fluid and the system can’t breath.

The “charcoal bed” is, simply, a bed of activated charcoal. “Activated” simply means bathed in acid to make it highly porous. A chunk of charcoal full of big pores has far more surface area than a solid chunk of the same size, and it’s the surfaces that attract the hydrocarbon molecules. Carbon bonds to carbon really readily, and charcoal is… you guessed it… carbon. But it’s designed to pass vapors, and not fluid.

Modern systems are designed with a diaphragm-operated check valve to prevent fluid from going down the vapor tube, so the OP’s car is likely okay.

Looking at the gas gauge is not accurate enough. I can run a hundred miles and the needle will still be on full.