# Purpose of dual gas tanks?
**URL:** https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075
**Category:** Factual Questions
**Created:** [August 8, 2005, 4:37am UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075 "2005-08-08T04:37:13Z")
**Posts on this page:** 18
**Page:** 2
### Author:  [@RedSwinglineOne](https://boards.straightdope.com/u/RedSwinglineOne)
#### Post date: [September 30, 2015, 3:57pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/21 "2015-09-30T15:57:31Z")
> [@LSLGuy](#):
>
> There’s not really a reserve “tank”. What there is is a single gas tank which has two fuel lines connected to it. The regular line connects about a half inch above the bottom. The reserve line connects at the bottom.
Actually, it all normally happens in the fuel valve itself. The valve has three settings, ON, OFF, RES. The valve is at the low point of the tank with a tube 1-2 inches long pointing upward. ON draws from the tip of the tube. REServe draws from the base of the tube. OFF is, off.
[Sample](http://www.dansmc.com/carbs_fuelpetcock1.jpg)
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### Author:  [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)
#### Post date: [September 30, 2015, 3:58pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/22 "2015-09-30T15:58:10Z")
I have an old F150 with an extended cab and an 8 foot bed. It has two tanks, a front tank and a rear tank. One is not a reserve. they are both 19 gallons each.
There is one fuel gauge, and a switch underneath it on the dash to select the front or rear tank. Whichever tank is selected is not only the one that is supplying fuel to the engine but it’s also the one that is connected to the fuel gauge on the dash. So if you want to see how much fuel is in the other tank you have to actually switch over to it.
The reason for two fuel tanks is kinda obvious. If you look under the truck, there isn’t room anywhere for one huge tank. There’s room at the back of the truck for one smaller tank, and room on both sides for a smaller tank, but the drive shaft prevents you from having enough room to put a really big tank right under the middle of the truck. So they put one in the back and one on one side, so that you can fill them up from the same side of the truck. If they balanced it out and put one on each side then you’d have to fill the other tank from the other side of the truck.
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### Author:  [@cornflakes](https://boards.straightdope.com/u/cornflakes)
#### Post date: [September 30, 2015, 4:02pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/23 "2015-09-30T16:02:34Z")
> [@Pushkin](#):
>
> Do bikes have two separate tanks?
…And just to round things out, the old Harleys and Indians had twin tanks, but these were separate tanks that were connected by tubing. They were probably made as separate tanks so that they could fit around the frame. The gas petcocks were still set up to draw from a lower level when switched to reserve.
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### Author:  [@Just\_Asking\_Questions](https://boards.straightdope.com/u/Just_Asking_Questions)
#### Post date: [September 30, 2015, 4:47pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/24 "2015-09-30T16:47:46Z")
> [@ss457](#):
>
> The difference in tanks is the regulations at the time on how much fuel you can haul in a standard vehicle. Two tanks gave more capacity with laws at the time. The bigger trucks only had one big tank if they are diesels because they fall under different regulations than gasoline. A tank can only hold 37 gallons of gasoline without having to be placard and require a cdl driver with todays laws. I.e a 37 gallon transfer tank can be rated for gasoline and anything bigger will say it is for fuel oils (diesel)
I don’t know where you’re getting your info, but I think it is incorrect.
Regulations for fuel hauling you are citing are for bulk carriage, not actual vehicle fuel tanks. Even so, the maximum quantity haul-able without being placarded is 119 gallons IIRC.
Large semi trucks routinely have two 100 gallon or more fuel tanks, and they aren’t placarded. The reason pickups have two tanks is because of 1) cost and 2) space. You can fit two smaller tanks in a pickup a lot easier than on big one. Also, having two tanks means for normal driving you don’t have to fill both, saving cost and weight.
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### Author:  [@herman\_and\_bill](https://boards.straightdope.com/u/herman_and_bill)
#### Post date: [September 30, 2015, 5:24pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/25 "2015-09-30T17:24:49Z")
Like a Pontiac from Arizona, another thread has risen from the ashes.
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### Author:  [@Kimballkid](https://boards.straightdope.com/u/Kimballkid)
#### Post date: [September 30, 2015, 6:28pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/26 "2015-09-30T18:28:08Z")
> [@engineer\_comp\_geek](#):
>
> If they balanced it out and put one on each side then you’d have to fill the other tank from the other side of the truck.
I had an '83 GMC pickup like that and it was a big pain in the ass.
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### Author:  [@Kimballkid](https://boards.straightdope.com/u/Kimballkid)
#### Post date: [September 30, 2015, 6:29pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/27 "2015-09-30T18:29:12Z")
> [@herman\_and\_bill](#):
>
> Like a Pontiac from Arizona, another thread has risen from the ashes.
Pontiacs come/came from Detroit.
🙂
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### Author:  [@Critical1](https://boards.straightdope.com/u/Critical1)
#### Post date: [September 30, 2015, 6:37pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/28 "2015-09-30T18:37:19Z")
2 Tanks is also more fuel per fill up meaning fewer fill ups meaning less time spent getting gas, even if its a pain in the ass to fill them both up its still easier than doubling your trips to the station.
If you have ever commuted on a motorcycle you probably know what I mean. Mine pulled 50 or so to the gallon but had a 2 gallon tank. Meaning triple the fill ups compared to my car which got 300 or so per tank.
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### Author:  [@leftfield6](https://boards.straightdope.com/u/leftfield6)
#### Post date: [September 30, 2015, 6:47pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/29 "2015-09-30T18:47:55Z")
> [@herman\_and\_bill](#):
>
> Like a Pontiac from Arizona, another thread has risen from the ashes.
Well, as long as it’s already up and moving around, I’ll nudge it a little more!
I have a fairly normal 2 door CAR with two fuel tanks. 1983 BMW 320i. It has two fuel tanks because it was the best way to creatively fit an acceptable amount of fuel into a space that was split by the drive shaft. No reserve function at all, the tanks are connected via a large hose, so fuel pickup is just in one tank. The “added-on” tank is filled or emptied just by it’s connection to the other tank.
So, one case here of it was definitely done just for the packaging.
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### Author:  [@Doughbag](https://boards.straightdope.com/u/Doughbag)
#### Post date: [September 30, 2015, 7:17pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/30 "2015-09-30T19:17:18Z")
[They still install a 2nd fuel tank](https://www.youtube.com/watch?v=df6wL6cFuoI)
Mostly its for range.
Here in Europe a few people have “switchable” duel fuel tanks, to burn cheaper farm diesel from one tank while “working on the farm” and regular diesel when on the public road.
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### Author:  [@Pinmin](https://boards.straightdope.com/u/Pinmin)
#### Post date: [October 1, 2015, 1:57am UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/31 "2015-10-01T01:57:45Z")
> [@Kimballkid](#):
>
> I had an '83 GMC pickup like that and it was a big pain in the ass.
Park in between pumps and fill from both sides at the same time. We did that a lot in our old Chevy.
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### Author:  [@Kenm](https://boards.straightdope.com/u/Kenm)
#### Post date: [October 1, 2015, 3:02am UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/32 "2015-10-01T03:02:28Z")
[**Speaking of old Chevy pickup gas tanks,**](http://www.autosafety.org/history-gm-side-saddle-gas-tank-defect) and lest we forget 2,000 people were burned alive for the sake of $2.20 a truck:
> [@](#):
>
> Based on data from the Fatality Analysis Reporting System (formerly known as the Fatal Accident Reporting System), over 2,000 people were killed in fire crashes involving these trucks from 1973 through 2009. . . .
>
> . . . At the heart of GM’s resistance to improving the safety of its fuel systems was a cost benefit analysis done by Edward Ivey which concluded that it was not cost effective for GM to spend more than $2.20 per vehicle to prevent a fire death. (Attachment N.) When deposed about his cost benefit analysis, Mr. Ivey was asked whether he could identify a more hazardous location for the fuel tank on a GM pickup than outside the frame. Mr. Ivey responded, “Well yes…You could put in on the front bumper.” (Video: “Ed Ivey Deposition,” Attachment O is a copy of this portion of the deposition.) GM was able to hide all this evidence and much more from the public until the early 1990’s when leaks in GM’s secrecy dam started and the Center for Auto Safety began to focus in on the defect.
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### Author:  [@Me\_Billy](https://boards.straightdope.com/u/Me_Billy)
#### Post date: [October 1, 2015, 3:18pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/33 "2015-10-01T15:18:50Z")
Some people use their pick-up for around town driving only. They can fill up with gas anywhere.
Other people may use the pick-up for a camper or towing a trailer - travel long distances. Some places like western Texas may not have gas stations for a long distance, so travelers like a truck with more fuel capacity.
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### Author:  [@Son\_of\_a\_Rich](https://boards.straightdope.com/u/Son_of_a_Rich)
#### Post date: [October 1, 2015, 3:54pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/34 "2015-10-01T15:54:06Z")
Our '61 VW Bug had a reserve like a motorcycle, with a foot operated valve forward of the shifter. I could never remember what position was what. AFAIK, once fuel gauges were standard equipment, that feature was eliminated. Same for motorcycles- my '04 Honda has a gas gauge, no reserve.
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### Author:  [@Kimballkid](https://boards.straightdope.com/u/Kimballkid)
#### Post date: [October 1, 2015, 6:04pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/35 "2015-10-01T18:04:11Z")
> [@Pinmin](#):
>
> Park in between pumps and fill from both sides at the same time. We did that a lot in our old Chevy.
I haven’t had that pickup in years so it’s no longer an issue. I’ve seen what you describe done before and I think it’s a dick move.
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### Author:  [@HoneyBadgerDC](https://boards.straightdope.com/u/HoneyBadgerDC)
#### Post date: [October 1, 2015, 6:48pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/36 "2015-10-01T18:48:10Z")
I have the same truck with dual tanks, I think they are twenty gallone each. These trucks would get pretty poor gas mileage with a camper on the back. Maybe less than 200 miles. This may not be enough to go to a remote location and then drive around for a week or two while you are there. There are times when 40 gallons in not really enough.
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### Author:  [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)
#### Post date: [October 1, 2015, 6:58pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/37 "2015-10-01T18:58:19Z")
> [@Kenm](#):
>
> [**Speaking of old Chevy pickup gas tanks,**](http://www.autosafety.org/history-gm-side-saddle-gas-tank-defect) and lest we forget 2,000 people were burned alive for the sake of $2.20 a truck:
Probably more like 150. The Chevy C/K saddle tanks thing is one of the more flagrant examples of an automotive moral panic. (See also: Corvair, Pinto, Toyota acceleration, etc.) The _Dateline_ segment that set it off was later shown to be deliberately faked, and independent studies didn’t come even close to agreeing with CAS’ ridiculously high fatality numbers. [Chevrolet C/K - Wikipedia](https://en.wikipedia.org/wiki/Chevrolet_C/K#Sidesaddle_fuel_tank_controversy)
The saddle tank design was not ideal, but the effect on the truck’s overall safety record was statistically insignificant. They were just as safe (or not, more realistically) as the equivalent full size pickups made by Ford and Dodge. It was also WAY safer than previous generations of trucks that had the tanks in the cab behind the seats.
> [@boytyperanma](#):
>
> Twin tanks also brings in some redundancy which can be important in isolated areas. Many of the trucks also have two fuel pumps. So if a tank leaks or a fuel pump fails you still have options to work with.
The requirement of two in-tank fuel pumps is probably what did away with the dual tank setups. With a carburetor and manual fuel pump all you need is the cheapo selector valve and a bit of extra fuel line. With EFI you need the two fuel pumps and the associated wiring. Plus in-tank fuel pumps don’t like being run out of fuel, which you’d be doing all the time on the primary tank. When fuel injection began to be offered in trucks in the late 80’s, you could get an FI-ed truck with two tanks and two fuel pumps but it was only a stopgap measure until they eliminated the dual tank setup in the next redesign.
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### Author:  [@Kenm](https://boards.straightdope.com/u/Kenm)
#### Post date: [October 1, 2015, 8:38pm UTC](https://boards.straightdope.com/t/purpose-of-dual-gas-tanks/316075/38 "2015-10-01T20:38:14Z")
> [@GreasyJack](#):
>
> Probably more like 150. The Chevy C/K saddle tanks thing is one of the more flagrant examples of an automotive moral panic. (See also: Corvair, Pinto, Toyota acceleration, etc.) The _Dateline_ segment that set it off was later shown to be deliberately faked, and independent studies didn’t come even close to agreeing with CAS’ ridiculously high fatality numbers. [Chevrolet C/K - Wikipedia](https://en.wikipedia.org/wiki/Chevrolet_C/K#Sidesaddle_fuel_tank_controversy)
Thanks for that. By this time I should expect faked reports.
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