# Siphoning Gasoline **URL:** \ **Category:** Factual Questions\ **Created:** [December 21, 2003, 8:39am UTC](https://boards.straightdope.com/t/siphoning-gasoline/220293 "2003-12-21T08:39:35Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Theios](https://avatars.discourse-cdn.com/v4/letter/t/e8c25b/32.png) [@Theios](https://boards.straightdope.com/u/Theios)\ **Post date:** [December 21, 2003, 8:39am UTC](https://boards.straightdope.com/t/siphoning-gasoline/220293/1 "2003-12-21T08:39:35Z")
Several weeks ago, I needed to siphon some gas out of my vehicle for some lawn equipment. Despite the fact that I used to do this all the time as a kid, I couldn’t do it. I was trying to do this with a small handheld pump designed for siphoning. My problem was that I couldn’t get the tube down to the gas. Is there some kind of block in modern vehicles that would prevent me from sticking a tube down to the gas? Or am I just an idiot? I tried all four vehicles I own. 83 Jeep CJ-7, 86 Jeep CJ-7, 2001 Jeep Cherokee, 94 Ford Escort. When I was a kid, I could siphon out of early 70’s Chevy cars and trunks with a peice of garden hose. The tube for the hand pump is slightly smaller that a cheap garden hose (I think, I’ll have to double check) ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [December 21, 2003, 8:51am UTC](https://boards.straightdope.com/t/siphoning-gasoline/220293/2 "2003-12-21T08:51:54Z")
> [@](#): > > \*Originally posted by Theios \* > \*\* The tube for the hand pump is slightly smaller that a cheap garden hose (I think, I’ll have to double check) \*\* A tube that big is too big to snake down into the tank. I use a tube with an outer diameter of 3/8" or less. ---
**Author:** ![Theios](https://avatars.discourse-cdn.com/v4/letter/t/e8c25b/32.png) [@Theios](https://boards.straightdope.com/u/Theios)\ **Post date:** [December 21, 2003, 9:21am UTC](https://boards.straightdope.com/t/siphoning-gasoline/220293/3 "2003-12-21T09:21:00Z")
Are the filler tubes on more modern vehicles smaller? I could use a cheap garden hose on the older ones, so that must be the case. I’ll nab some 3/8 hose from somewhere and see if I can cram that down the filler tube. ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [December 21, 2003, 3:01pm UTC](https://boards.straightdope.com/t/siphoning-gasoline/220293/4 "2003-12-21T15:01:34Z")
I’m guessing that your old siphon pump simply doesn’t work anymore. Either the bellows is cracked, or the check valve flapper no longer works. Flexy plastic doesn’t flex forever, especially when exposed to harsh chemicals and fumes. ---
**Author:** ![Thin\_Ice](https://avatars.discourse-cdn.com/v4/letter/t/aeb1de/32.png) [@Thin\_Ice](https://boards.straightdope.com/u/Thin_Ice)\ **Post date:** [December 21, 2003, 3:26pm UTC](https://boards.straightdope.com/t/siphoning-gasoline/220293/5 "2003-12-21T15:26:47Z")
Back during the days when you could get leaded as well as unleaded gasoline, there had to be a way to keep leaded gas from getting into unleaded systems (leaded gas ruins catalytic converters) so manufacturers designed smaller filler openings for autos that ran on unleaded and smaller nozzles for unleaded pumps. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [December 21, 2003, 4:05pm UTC](https://boards.straightdope.com/t/siphoning-gasoline/220293/6 "2003-12-21T16:05:17Z")
Make sure that’s 3/8 **OD** (outer diameter) hose. Generally hose sizes are by **inner** diameter, so a hose **labeled** as 3/8 could be too big. The filler restrictor for unleaded gas nozzles is at the top of the filler tube, just under the gas cap. A hose too big for it won’t go more than an inch or so down. Past that, the problem with getting a hose down far enough has to do with the bends in the filler tube, and sometimes a smaller diameter (than the 3+" filler tube) insert in part of it (reason for that insert? beats me). Whatever hose you use, the way to determine if it’s reached the fuel is to blow into it. It’s like blowing into a straw – you can tell if the tip is out in the air or immersed in liquid. ---
**Author:** ![herman\_and\_bill](https://avatars.discourse-cdn.com/v4/letter/h/f1d935/32.png) [@herman\_and\_bill](https://boards.straightdope.com/u/herman_and_bill)\ **Post date:** [December 21, 2003, 4:37pm UTC](https://boards.straightdope.com/t/siphoning-gasoline/220293/7 "2003-12-21T16:37:23Z")
Your fuel tank might have some kind of a flapper valve to prevent fuel from running out in case of a rollover. Your hose doesn’t have enough stiffness to get past the valve, and if it did it possibly could get stuck in the filler neck requiring dissambly to remove it. ---
**Author:** ![Theios](https://avatars.discourse-cdn.com/v4/letter/t/e8c25b/32.png) [@Theios](https://boards.straightdope.com/u/Theios)\ **Post date:** [December 22, 2003, 12:25am UTC](https://boards.straightdope.com/t/siphoning-gasoline/220293/8 "2003-12-22T00:25:00Z")
> [@](#): > > \*Originally posted by AskNott \* > \*\*I’m guessing that your old siphon pump simply doesn’t work anymore. Either the bellows is cracked, or the check valve flapper no longer works. Flexy plastic doesn’t flex forever, especially when exposed to harsh chemicals and fumes. \*\* It’s a fairly new pump. I was checking to see if I had gas on the hose when I pulled it out. It didn’t. I’m pretty sure **Gary T** is right. Sometimes I could jimmy the tube further down, just not far enough. **herman\_and\_bill** Raises a good point though. The Jeeps just might have something like that, since they were designed for off-road. I’ll experiment with my wrecked Jeep first. That one is getting taken apart anyway for a rebuild. ---
**Author:** ![Gary\_T](https://avatars.discourse-cdn.com/v4/letter/g/3ec8ea/32.png) [@Gary\_T](https://boards.straightdope.com/u/Gary_T)\ **Post date:** [December 22, 2003, 5:47am UTC](https://boards.straightdope.com/t/siphoning-gasoline/220293/9 "2003-12-22T05:47:43Z")
Some more tips: The hose has to be flexible enough to make the bends, but stiff enough to push through rather than just bunch up. When you feel the hose resisting, as though it has bumped up against something, start rotating it while pushing gently. Often that will enable the hose tip to jump over a ridge (e.g. the edge of the tank neck inside the rubber filler hose). ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [December 22, 2003, 11:08am UTC](https://boards.straightdope.com/t/siphoning-gasoline/220293/10 "2003-12-22T11:08:36Z")
Lots (all?) tanks have something called a “rollover valve” in the fuel tank. A spring pushes against it to cork the filler neck. If the car rolls over, no gas spills out. This spring is really weak, though, so when you put in gasoline, it opens from just the weight of the gasoline. The mechanics of the rollover valve mechanism, though, are probably what’s preventing the hose from going in. I think you’d need a _really_ thin hose to get into it.