We’ve all been there before – feeling frazzled, stressed out, or distracted, we end up doing something a little goofy that we couldn’t have imagined doing before.
Something like driving through a car wash with our gas cap off (and maybe even our gas cap door wide open, too).
Water doesn’t belong anywhere in the gas tank and can cause serious problems if it finds a way in. But while you might think that a car wash would fill your tank with soapy water, the truth is you might be in better shape than you realize. You might not have much to worry about at all!
In the rest of this quick guide, we cover almost everything you need to know about what happens when you go through the car wash, what you need to worry about, and what you can do to fix the problem.
What happens if you go through the car wash with your gas cap off?
Believe it or not, you might not end up getting a ton of water in your gas tank – even if you go through a carwash with the gas cap completely off.
The design of modern gas tanks (and the cap system itself) helps to protect against these kinds of accidents and mistakes.
There’s not only a metal flap that usually covers the tank fill channel (it gets depressing when you put a gas nozzle in), but the fill channel is also angled down and away from the car.
It’s tough for a lot of water to get in, short of hosing water directly into the fill channel.
It doesn’t mean that water can’t get into the tank. And it doesn’t take a lot of water in your tank to cause serious problems (including hydro locking of your cylinders, a worst-case scenario that’s always expensive to fix.
Is the car running ok?
Because so little water can cause so many issues (combustion issues in particular), you’ll know immediately whether or not water in the tank is troublesome.
If you could drive home from the car wash without any issues, only then realizing that the gas cap was open, you’re probably not in too much trouble.
You’ll still want to be on the lookout for issues – combustion problems, hard starting, stalling, etc. – but you’re likely ok.
Suppose you are having trouble with your vehicle immediately, maybe even at the car wash. In that case, it’s a good idea to shut your car off (as soon as possible) and work to remove the water immediately.
Add a bit of dry gas to the tank
Using a little dry gas is the easiest fix for just a little water in the tank.
Made with formulas that include methanol or isopropyl alcohol, dry gas eliminates water in your tank by binding to the actual water molecules. The combo is then sent through the fuel system into the combustion chamber and is safely burned up.
All you have to do is add the right amount of dry gas to your tank (based on how much fuel is already in there) and let it do its magic. You don’t have to do anything else, and dry gas works immediately.
You might want to siphon the bottom to be sure
Maybe you don’t have dry gas, can’t get some in time, or want to be certain that there’s no water in your tank – seeing the proof with your own two eyes.
If that’s the case, and your vehicle doesn’t have anti-siphon blockers in the fill channel, you can feed a siphon down to the bottom of your fuel tank and see what comes up.
Because water is a heavier liquid than gasoline, all the water that made it into your tank will collect on the bottom of the fuel tank itself. If there is any water, it’ll pool right next to the fuel pickup.
You don’t need to go wild with your siphon, either. Just pull a couple of cups of fuel from the tank and look at what you’re working with. You’ll be able to see the water under the fuel if you give it a couple of minutes to separate.
If there’s water in the tank, you can siphon more and more fuel until you get rid of the water entirely. It shouldn’t take very long. Just keep pulling fuel out until it’s free of water entirely.
If you’re nervous, drain the tank completely
Let’s say that you’re nervous about water ending up in your tank – or worse, throughout the rest of your fuel system.
You could always drain your tank completely and start with fresh fuel. It’ll take a little longer to siphon everything out of your tank (maybe 30 minutes), but you won’t have to worry even a little that there’s even a drop of water.
It should only ever be used as a last resort kind of option. You’ll end up wasting an entire tank of gas (and that’s never cheap) and need fresh fuel on hand – at least enough to get you to the gas station so you can fill up.
Closing thoughts
While no one would recommend you drive through the car wash with your gas cap off and your fuel door open, it might not be the doomsday scenario you’re likely dreading.
It’s not a great thing to happen. Still, modern auto design usually protects water from getting into your tank more than you think.
On top of that, you can use any of the solutions we highlighted above to fix this problem without too much headache, hassle, or money.