This Cheap Tool Makes Getting Old Gas Out Of A Tank Crazy Easy

One of the more annoying steps of a car revival is figuring out what to do with a tank of old gas. If you’re lucky, the vehicle you’re trying to bring back to life has a drain at the bottom of its tank. If it doesn’t, you’re sometimes left deploying the old-school siphon. Old-school car enthusiasts almost certainly know the taste of gas from starting a siphon with a mouth, but there’s a better way. For less than $15 all you have to do is shake a tube and let the tank drain itself. I’m serious.

This year, I’ve embarked on my first-ever classic car revival. Admittedly, work is going slow, but I’m now making regular progress. Since starting work on my 1948 Plymouth Special DeLuxe, I cleaned the giant spiders out of the vehicle, freed up its mighty flathead straight-six, tested its electrical system, and rebuilt its carburetor. I’ve also confirmed that the car has working brakes, a shifting transmission, a grabbing clutch, and even working lights.

I feel like we’re only just a few more fixes away from the car’s first start in nearly a decade. But before I can get there, I have to remove the rotted old fuel from the vehicle’s tank.

While this may be my first car revival, I’ve brought several motorcycles back from the dead in the past. Thankfully, my years of wrenching on bikes and watching Vice Grip Garage have seemingly primed me to work on this Plymouth. There’s a lot that feels familiar even though I’ve never worked on a classic car before. The carburetor seemed similar enough to the carbs I’ve fixed on old motorcycles. The ignition and electrical systems are also pretty simple, like I’ve experienced on older bikes.

But this time I’ve decided to do something different. When I revived motorcycles in the past, I had two methods for dealing with old gas. Often, I just topped up the tank with new gas, installed a fuel filter, and sent it. Truth be told, most of the time this worked out just fine. The engines were never super happy to burn years-old gas, but eventually all of the bad stuff got burned away and nasty fragments got caught by the filter. Chances are you’ve read that gas begins to break down after only six months. While that may be true, even broken down gas can burn long after that six-month mark. Will it be great fuel? No, but it can burn.

There have been times when this strategy bit me, such as when particles apparently got past fuel filters and clogged up my motorcycle carburetors. So, sometimes, I did the old-school way of emptying tanks and sucked on a tube inserted into the tank to start a siphon process. But let’s be real here, tasting decade-old gas sucks and I reckon 10 out of 10 doctors would recommend against doing that for your health.

You can also buy transfer tubes with hand-squeeze pumps (like the ones you get with blood pressure cuffs) on them. But in my experience, they work maybe once or twice before failing.

A few months ago I saw the answer.

I’m not sure what YouTube channel I was watching. Or, heck, maybe I was watching a friend wrench. All I know is that the person whipped out the same rubber tube you’d use to siphon gas out of a tank. But at the end of the tube was something unexpected. The end of the tube featured a metal end with a marble captured inside of it. When you shook the tube, a siphon gets started without any sucking on your part.

I had to get one of my own. Sure enough, for just $12 on the jungle site you can get a six-foot hose with a valve on the end. Amusingly, Harvard University has a simple mathematical explanation for how a siphon works:

A siphon is a device that allows the transfer of a fluid from one reservoir to a second at a lower level even though the first part of the journey is up-hill. A siphon is effectively an inverted U-tube with unequal length tubes. The asymmetry means that there is a pressure difference between the ends;

at the upper reservoir: p1 = P – ρgh1
at the lower reservoir: p2 = P – ρgh2
(where P = atmospheric pressure)

So p1 > p2 if h2 > h1 and the fluid flows. To get the siphon ‘running’ you do need to reduce p2 and the best way is orally by sucking on the tube (this is why we use water rather than gasoline which would have been be easier to see), but once the head difference is achieved the process is automatic.

The University of Nevada has more details:

When both legs of the siphon are full, because of gravity, the hydrostatic force (the force of the water) is greater on the higher side of the tube. This means the liquid will move up the lower leg of the tube, over the rim of the beaker and into the lower beaker. Once started the flow will continue until the water levels are equal. Then the hydrostatic forces on each leg of the tube will also be equal.

In theory, the marble inside of the valve of this newfangled siphon is just doing what your mouth used to. Only now you don’t need your mouth to do it.

Update: I’ve been informed that auto-siphons have been around for decades. If you, like me, have been sucking on tubes for years, we’ve been doing things the wrong way for too long!

Still, I couldn’t believe it even when I saw it with my own eyes. My favorite car revival YouTuber, Derek Bieri of Vice Grip Garage, calls these things “Alabama Credit Cards” and even in his hands they work like magic.

Setting up my “credit card” to work on my Plymouth was stupid easy. I just unraveled the hose, stuck one end into the Plymouth’s fuel tank, stuck the other end into an empty fuel container, and then shook it a bunch of times like a shake weight. Sure enough, I began seeing fuel in the hose. Once the fuel reached most of the way through the tube, the process became entirely automatic.

By my estimate, there was a little bit over three gallons of bad fuel in the Plymouth’s fuel tank. But here’s the awesome part: The fuel didn’t look that bad!

I mean, yes, it did smell varnished and the fuel was a little bit on the brown side. However, I didn’t see any major particles and the fuel still ignited when I lit it up. I then dragged the siphon across the bottom of the tank, where I got more fuel, but no rust or anything too nasty like that.

I’ve brought back motorcycles that had substantially worse gas than this. If I had to wager a guess, the car’s previous owner, Willie, probably put ethanol-free fuel in this baby. I can’t wait to take a picture of this thing once it emerges from the operating room that is my tiny apartment garage.

With removing the old gas out of the way, I put some fresh fuel in the tank, mounted up the rebuilt carburetor, primed the carburetor, and then let the car rip. The engine easily spun over, but didn’t fire. Sure enough, the Plymouth isn’t making any spark.

In fairness, I did expect that. I just got so excited I skipped the ignition system entirely. I do have the parts to rebuild the ignition system, but I’ll first try to get things going by cleaning the points first. This car is so close to running, I can feel it! I’m sure the fuel tank probably still has some nasty bits left in it, and I’ll run some filters for now. Ideally, the whole tank needs to come down to be cleaned, but that’s something for another day.

But the triumph of getting this engine running will hopefully be a story I get to write really soon. For now, I just want to marvel at the usefulness of this cheap tool. I think my dentist and my doctor will agree that this auto siphon glockenspiel is some of the best $12 I’ve ever spent.

(Images: Author)

[Ed note: This post contains an Amazon affiliate link, and if you click it and buy stuff we’ll probably get a small commission.  MH]