Sometimes an automaker wants to, or is required to, offer multiple fuel tank sizes, and because blow-moulding a different-size fuel tank is prohibitively expensive, carmakers tend to employ rather ridiculous methods to achieve their goal. Among my favorite example is the Jeep Wrangler YJ’s “rubber hose” trick, which allows owners to increase their fuel tank size by 5 gallons for free by simply cutting a hose. Allow me to explain.
Before I jump into the Jeep YJ’s crazy fuel tank limitation strategy, I’ll first talk about another, more modern vehicle that changes its fuel tank “size” via a ridiculous method: The BMW i3.
As you know, I adore my 2021 BMW i3S Giga World in Galvanic Gold just like I adored the 2014 model that I owned before. But to get the most out of the latter, I had to actually go in and “code” the car to increase its gas tank size. Yes, you read that right — I could digitally change the size of the car’s fuel tank.
Changing The Gas Tank Size Using A Cell Phone
Here’s a look at the section of “Bimmercode,” via YouTuber SimpleCarGuy, that allows you to, via your cell phone connected to a bluetooth OBDII dongle, “increase electronically limited fuel capacity”:
The BMW i3’s fuel tank has a capacity of 2.4 gallons, but for U.S.-sold 2014 to 2016 BMW i3 REXs, which have an EPA-estimated EV range of only 72 miles, the gas tank had to be limited to just 1.9 gallons in order to qualify as a “BEVx” in the eyes of California. The Truth About Cars breaks it down, writing:
Rather than an actual percentage of cars sold, CARB created a credit system where an alphabet soup of classifications (PZEV, AT-PZEV, TZEV, etc) get partial credits and true ZEVs can get multiple credits. Into this complicated world came the unicorn that is the BEVx. Despite having a gasoline burning engine, BEVxs get the same credits as a vehicle with the same range and no dinosaur-burner. The distinction is important and critical. If the BEVx requirements are met, the i3 gets the same 2.5 credits as the i3 EV, if not it would get a fractional credit just like a regular Prius. The requirements are: the fossil fuel range must be less or equal to the EV range…the battery must deplete to a low level before the generator kicks in and may not be charged above that level. In addition the fossil fuel generator or APU must meet CA’s SULEV emissions standards and have a long battery warranty.
So, with the gasoline range extender helping the car get about 35 MPG, at 2.4 gallons, the little 647cc scooter motor would be able to propel the car 84 miles — a dozen miles over the 72 mile EV range. To solve this, BMW simply prevented the user from accessing all 2.4 gallons. It’s not 100% clear how BMW accomplishes this, but I assume the car shuts the fuel pump off after a certain volume has flowed out of the tank and into the engine.
In just a few minutes, a BMW i3 owner can not only increase their tank size by half a gallon (and thus increase their driving range by about 18 miles), but they can also code out the other BEVx requirement via something called “Hold State Of Charge,” which lets the engine cut on at 75% battery capacity (versus the ~6.5% required by California), thus avoiding the battery dropping close to 0% state-of-charge when climbing hills and possibly having to slow the car down.
This is a quick way to get more fuel tank capacity, and while the Jeep Wrangler YJ mod takes more time since it’s a mechanical fix versus a digital one, the results are much more dramatic than the BMW i3’s extra half a gallon.
Cutting A Small Rubber Tube Gets You An Extra 5 Gallons
This is something I came across while trying to fix a gas smell from my YJ, though one of you dear commenters recently brought it up, inspiring me to write this.
If you look at the Jeep YJ from the rear, you can see, hanging down below, a skid plate protecting its fuel tank:
At 20 gallons, that’s a huge tank; several modern mid-size trucks have smaller ones. But on certain Jeep YJs — mostly four-cylinder ones — the tank is actually specified as only a 15-gallon unit. That’s because Jeep “artificially” reduced its capacity, but unlike BMW who used a computer to do so, Jeep just employed the use of a rubber tube.
YouTuber JeepSolid shows the pressed-in tube in his video; the screenshot below shows that tube on the right:
As JeepSolid shows, to increase the fuel capacity, you simply yank the tube out with some vice grips and cut it down from about 10 inches to 2.75 inches or so:
Another YouTuber, Plane Simple, just removed the tube entirely and it seems to work fine (some warn that it could lead to some over-filling/splashing). He illustrates just how far the 15-gallon tank’s vent tube reaches down into the tank:
As JeepSolid points out, the longer vent tube restricts fuel flow because once the liquid gasoline covers the bottom of the tube, all gases must escape the tank through the filler neck, triggering the gasoline nozzle at the gas station to shut off flow:
Shortening or removing the vent tube means liquid gasoline must reach way up into or near the filler neck before the gases shuts off the nozzle.
The downsides to this free mod are few. Obviously, the fuel gauge will read “F” for a very, very long time, since even 15 gallons is considered a full tank to that sending unit. But otherwise, it’s a truly free improvement.
You do have to wonder why Jeep did this in the first place, and while I initially thought the reason was to force shoppers to pay extra for a “big capacity” tank, I’m finding some admittedly less-than-primary sources that say otherwise. Here’s what T-Rex Auto Parts says:
Why did Jeep put a restrictor pipe in the 1991-1995 Wrangler YJ gas tank?
Answer: From what we have been told, Jeep needed to meet Federal Café Standards on fuel mileage per gallon within their lineup, so by reducing this tank by 5 gallons (approx. 40 lbs) they were able to increase the MPG on this vehicle and be within the Federal guidelines.
So they did it to save weight? I don’t buy that. Not only does 5 gallons weigh about 31 pounds (not 40 pounds), I’m fairly sure the EPA’s FTP-75 drive cycle specifies that vehicles are to have their tanks filled at 40%. So that means a 15 gallon tank would have 6 gallons in it and a 20 gallon tank would have 8 gallons in it; that’s a delta of only two gallons — or about 12-ish pounds.
Though this could be an issue of EPA “Test Weight Class,” I think the reality is that the YJ offered the “extra capacity” fuel tank as an option on the Wrangler, Wrangler Base, and Wrangler Islander, while the Sahara and Renegade came with the big tank as standard. My intuition tells me that Google AI is full of it, and the real reason has pretty much nothing to do with the EPA, and everything to do with maximizing profit.
Regardless, it’s a fascinating and incredibly primitive solution.
Top Image: Jeep
Despite this article being about the YJ, my takeaway is that Cali’s rules kneecapped the i3 from being a nearly perfect EREV.
While rules and regs are important, this is a prime example of legislation getting in it’s own way.
EREVs are the perfect bridge electric vehicle for a ton of people. Their daily commutes could be 100% battery powered, with the gas engine supplementing longer rides or trips without ample charging available. As hybrids prove, Americans aren’t anti electric or anti EV, they don’t want to make huge (even if it’s mostly perceived) compromises on how they use their cars currently.
It’s the buffet problem. People are willing to pay extra for the perceived benefit of having access to more options, even if they never make use of them. People pay more for the buffet rather than a single entree because they want the options available.
And this isn’t novel with car markets – tons of people buy Mustangs that they never take on the track, Jeeps that they never take offroad, and trucks that they never tow with. Literally every car marketer knows this.
Yet with EV’s, it comes as a surprise both to regulators as well as marketing teams that, yes, being able to cover 80% of daily commutes in any given month with an EV is insufficient for most consumers; even if they rarely have a need to take an extended drive, consumers want to have that option without being unduly inconvenienced. That makes EV’s untenable for, particularly, single people (where they are likely only to have one car) whose social network exceeds the reach of their car’s range or convenient chargers. California could have achieved the same environmental (arguably, even more positive) impact by encouraging adoption by alleviating genuine range problems rather than doing what they did, which is over-regulation that lead to withdrawal of good offerings from the market.
Agreed, glad Chevrolet didn’t bother going for this cert with the Volt. I have total freedom of when to run the engine, regardless of battery state of charge, which is more useful than you might think. It allows the Volt to be an actual car, even though the fuel tank is still piddly (9 gals or so), I can still go a long way on just that.
This is so typical of the Left in this country. They are sooo good at these nitpicky rules and regulations that ultimately turn off people who would otherwise probably champion many of their causes.
I’m sure one of the main reasons to buying a piece of crap like the i3 were for environmental reasons. At least for some. So instead of encouraging folks to buy an EV with a backup ICE, they purposefully handicap it to (presumably) go for a full EV instead. Such stupid thinking and manipulation. This shit drives me nuts, and I say that as someone who typically is Left on most issues out there. Leftist groups just seem to find ways to piss you off.
The manner in which CARB allocated the credits on the i3 REV is a bonus, not a fault. BMW could have built the car in the configuration used in other markets, BUT if they did that, they would have only received a partial credit as the car would be (correctly) considered a hybrid. By jumping through the “hoop” described, CARB was willing to pretend that the range extending ICE system did not exist and award the same multiple credits as the BEV model. As part of the deal, the car had to be configured to run as a BEV for the majority of the battery’s capacity. This is reasonable, since the car isn’t a BEV if the ICE range extender is running.
Very odd.
Could this just be to manage the total weight of passenger and cargo carrying capacity? Seems like the Wrangler would handle an extra 40 lbs or so but perhaps wanted to make sure you don’t overload it with too much stuff when off-roading.
None of the proposed reasons make sense.
If it was anything other than a wrangler, I’d blame weight distribution to balance out the 4cyl out front. Though I guess it could be to keep the front wheels from getting too light since the tank hangs off behind the rear axle.
Ok so per the article, 5G weighs 31 lbs so 20G weighs 124 lbs. would that much weight make a difference? I guess if you have that plus a fair amount of cargo in the back and off-roading means any lift off the front axle could be bad…
I like this explanation a lot more than what was mentioned. I vote we accept this and move on.
There was another comment I read further down that explained the EPA weight categories, which I think also makes a lot of sense.
Nonsense, we’ve moved on!
But seriously it makes sense but I prefer real-world “reasons” to compliance.
Can I just point out that the C.A.R.B. hodge podge of naming categories is just dumb.
This reminds me of my printer. When using brand name cartridges, it limits the number of pages you can print before declaring it’s out of ink. If you force it to print a test page, there’s clearly more ink, and a Google search confirmed this. Generic cartridges are the answer. I use refillable ones.
There’s never a bad time to post this evergreen comic from The Oatmeal.
My 350z’s tank has an engieering flaw as well.
It’s sort of a saddle shape that sits over top of the drive shaft, which means that if you’ve got close to a half tank, depending on how the gas sloshed around before you pulled up to the pump, you may not be able to put more than a gallon in before the gas pump clicks itself off. If you want a full tank, you basically have to wait until you’re on empty.
Around town it’s not a big deal, but it was REALLY annoying for the few road trips I did in it.
That describes most Jeeps made before 2000 pretty well, I’d say. It was one of the things I liked about them.
now those are Some Geniuses at jeep
I give the engineers a lot of credit. The management that ordered them to do it, not so much.
There is something sort of similar on Excursions, although with actual good reason.
They used the same fuel tank for the gas and diesel versions, which is a 44 gallon tank. Except actual capacity was closer to 50, and the filler neck stuck down a couple inches into the tank so when filled with gas there was some extra space for the vapors.
Since diesel doesn’t have the vapor issue that gasoline does, a common mod is the “harpoon mod” (no idea why they call it that) where you reach inside and cut off the extended filler neck to gain a few more gallons. Boom, ~50 gallon fuel tank. I believe my diesel Excursion had this done before I got it, I almost never run it all the way empty but I have gotten almost 44 gallons in when it wasn’t totally on E before. Super awesome to have that kind of range though. 900+ miles not towing is totally possible!
“… a common mod is the “harpoon mod” (no idea why they call it that) where you reach inside and cut off the extended filler neck…”
Step One: Find a person with very small hands.
Or Captain Ahab.
It only works on white ones.
“The requirements are: the fossil fuel range must be less or equal to the EV range…”
Yeah that’s just plain dumb. The $15K BYD hybrid sedans manage 1000+ miles with 17 gal. tanks and just 30 miles of electric range. It would be unthinkable to have them kneecapped to just 60 miles!
Sure but they don’t call it a BEV, they properly designate it as a hybrid, and thus this rule wouldn’t apply. The dumb thing would be if they tried to pretend it was a BEV with only 30 miles of battery and a 17 gallon fuel tank.
Ahh true true.
Yay government! Regulate me harder daddy!
Imagine if someone had the time to go through all the bullshit regulations and rules and clear out all these stupid ones and loop-holes. That’s probably the best use of AI that I can think of. We have so many rules and regs these days I would bet, not a single person working at any of the agencies know half of them, let alone how to correctly enforce them.
“That’s probably the best use of AI that I can think of.”
That would be the best use of actual people I can think of.
Because after AI is done, we’d all have 5 1/2 wheeled cars and be turning left out of the upstairs lane.
My approach assumed human review after. Take a look at how many laws and codes and regulations etc… we have and how realistic it is that it would be done without some sort of computer usage.
actual humans got us into this mess, why not let our machine overlords have a crack at being less dumb?
also, I had no idea that you could turn left out of the upstairs lane. does a BMW turn signal indicate that? the world will never know.
BMWs have turn signals?
(German accent)
“Haff you paid ze subscription?”
That’s part of the problem: a big part of the time, the stupid hoops you have to jump through for regulations are because someone decided to be clever and find a loophole in the nice simple rules. Then the rules are made more complicated to close it. Then someone finds a new loophole. And every one of those extra rules to close a loophole brings the chance of unintended consequences along with it.
Basically, assholes who think they’re smarter than everyone else instead of just more of an asshole are the reason we can’t have nice things.
How does having more or fewer gallons in the tank affect the MPG? The fuel weight alone isn’t enough to materially affect MPG. So are the tests measuring the number of gallons as a % of the tank’s nominal size, instead of measuring the actual fuel being consumed? That’s kind of nuts.
Check out the comment from Bhautama below. The weight alone seems like it may have indeed been it.
To me, this is worse than the Tesla glass roof debacle. An extra 33% range makes a pretty big difference day-to-day with a vehicle.
Right, this is more like when Tesla was making lower range version but they still had the same battery pack they just didn’t let you use all of it.
Right. And even then, because you were using so much less of the battery, it degraded even less over time, so the gap slowly closed. But, you were carrying a lot of extra weight all the time, so that’s a huge demerit.
Hold the bus Marty. Jeep made some vehicles the gas gauge actually worked on??? My mind is blown………..
US Navy personnel could buy vehicles cheaper when overseas with US mainland delivery. After leaving Japan our ship was eligible for the program. I recall the big debate for Jeep buyers was paying extra for the bigger tank. No one knew at the time it was rubber hose that made the difference.
Bought my 93′ YJ used after returning. Still have it.
Wait until David learns that the air intake has a restrictor built into for the 4.0 that lowers the HP by 10 horsepower so that is did not have the same HP rating as the XJ’s Just one more classic American motors trick from back in the day
“Regardless, it’s a fascinating and incredibly primitive solution.” I halfway agree with you. It’s fascinating and incredibly shameful.
That could almost be one of Jason’s Phoning It In articles.
“To solve this, BMW simply prevented the user from accessing all 2.4 gallons. It’s not 100% clear how BMW accomplishes this, but I assume the car shuts the fuel pump off after a certain volume has flowed out of the tank and into the engine.”
I would bet that BMW doesn’t shut off the fuel.
My bet is that the fuel gauges and “low fuel” warnings are set to read as empty while you still have .4 gallons in the tank.
Why do I believe this to be true?
Because while my CLK350 has a 16.4 gallon fuel tank – when I have run the tank down so that all the readouts scream at me the car is in immediate danger of running completely dry – when I finally refill, I’ve never put more than 15.5 gallons into the car.
So what you’re doing to reprogram the BMW to access more fuel is merely changing the point when the car decides to inform you it’s running dry.
I smell another i3 “fill it all the way up and drive it till it is empty and the car wont go any more and then fill it back up to full” to test this theory
Using w/in “” as a blog post title might need some workshoping 🙂
Weight classes for EPA fuel economy are ‘binned’ in increments of 250 lb (4000, 4250, 4500, etc) or 500 lb when 5000 lb or higher. So if a vehicle’s weight is, say, 30 lb into the 4750 lb bin (ie 4530 lb), if they can cut 31 lb then they’re in the 4500 lb bin. Then your testing roadloads are calculated at 4500 lb. A full ‘tank’ of fuel is included in calculation of curb weight. So if you’re desperate for fuel economy at the last minute and can’t redesign a unique tank for this configuration, I guess I could see this happening. Related, though the EPA recommends a 40% full tank, the roadloads that are fed into the dyno are still the ‘bin’ masses I mentioned above.
I remember talking about “EPA Test Weight Classes” when I was at FCA, so yeah, I buy that.
Comment being pinned (added a note to the piece, too). Thank you!
Hey, David. At our shared OEM alma mater, the same thing was done on the AS and/or NS minivans. For the reasons noted, and the perennial focus on CWI, it also provided additional revenue for an optional larger capacity tank at essentially no extra OEM cost. The fuel tank remained a common part. I don’t recall the increased tank capacity, but something in my distant memory says maybe 2 gallons on the AS and more on the NS.
Back in the day the head engineer for the Mercury Marauder used to post on the Marauder forum. One of the things he “leaked” was the overview of the changes to be made for the still born 05 model. A number of those changes were to “add lightness” and get it into the 4000lb bin. That was of course to hit the CAFE target.
Since rounding is a thing a small increase can add 1 MPG to the test results.
Not strictly related, but it made me think of my mom’s 2013 Acura TSX which has the same gas tank (a robust 18.5 gallons) in both I4 and V6 variants.
She has the 2.4L I4 and it easily gets ~550 miles of highway range on a single tank which is nuts for a non-hybrid sedan of that era. It’s lowkey a great road trip car.
Loved my 2009 TSX I4.
I love my 08 Avalon for similar reasons, pure highway road tripping I can get nearly 500mi a tank if I feel like cooking the fuel pump. 350mi between refills is about the sweet spot, which means a single 15 minute stop to go as far as I can comfortably drive in a single day.
If you take it easy, 600 miles is achievable in the TSX in pure highway driving. Truly bladder-busting range, though it doesn’t hold a candle to Willard’s diesel Excursion mentioned above – 900+ miles on a single tank!!
On the first generation Fusion Hybrid the fuel tank was the same size as found on the ICE versions. That gave an easy 650mi range before the low fuel warning came on. In the second gen the Hybrid got a smaller tank and now I have to wonder if it was done the same way as the subject Jeep.
A large computer company I worked for many years ago ran out of the smaller hard drives offered on our laptops. The solution? Reformat the larger (optional) hard drives to match the capacity of the small hard drive and ship ‘em. Problem solved. I think it took about 15 minutes for somebody out there to figure it out and spread the word that re-formatting your brand-new drive could increase capacity by 25%!
The other way around, MicroShaft charged an EXORBITANT amount of money for a 120GB HDD for the Xbox360.
However, someone figured out that you could flash a Western Digital BEVS series drive to “think” it was an OE xbox 120GB.
So I grabbed a 160GB out of my stack of nerdery, and converted a “base” 20GB drive to a 120GB. I was MORE than willing to give up 40GB of space to save myself $200. I still have that xbox and the drive still works.
Apple charges usurious amounts for drive capacity bumps that cost very little. On the order of $400 for a 256GB increase, which costs $30-$50 when you buy the same capacity at retail. And they make sure you can’t upgrade the drive yourself without destroying the machine AND by tying the hardware to the motherboard (I.e. you need a “numbers matching” laptop for it to work).
Lenovo wanted to charge me $900 for a 2TB drive when I ordered my X1 carbon. I opted for the cheapest drive option and maximum RAM because only one of these was soldered to the board.
Thankfully, Lenovo doesn’t pull Apple BS and I got a 2TB for a great price and swapped it in.
For all their faults, Lenovo still makes Thinkpads partially users serviceable, and so that’s all I buy. I’m in my third since 2011.
I’ve owned at least 5 Thinkpads over the years. They’re my favourite design.
They’re not as nice as before IBM sold the line to Lenovo, but they’re still legit. They run most Linux distributions flawlessly out of the box, and some are even officially supported.
If serviceability is the priority, the Framework laptops may be worth a look.
I’ve heard of those! How’s the performance and reliability?
Decent I think, but depends a bit on which one and whether it’s on Linux or Windows. I know they had some issues with power savings mode initially, but so far as I know that’s resolved. Up-front price is a bit high for the specs, but that’s true of Lenovo’s serviceable models, too.
This sort of thing is why I never wanted an iPhone. Apple’s walled garden BS is just not customer-friendly. People would jail-break their own stuff and Apple jumped in and bricked them. People replaced their own batteries, so Apple started using security screws so you couldn’t open it without a special tool. They just completely failed to accept that once I purchase a product, it’s my choice to void the warranty or not.
I had similar issues with Sony for years, with their proprietary cables for video cameras. Haven’t bought any Sony nor Apple products in many years.
This plus proprietary connectors before the EU stopped in and inability to sideload. Unfortunately, the latter is going away because Google. I want my F-Droid!
Oh god. I had a 4 cylinder YJ many years ago. While I do miss the vehicle as a whole (totally rusty crusty, but fun to drive and a total beater, so I just did whatever I wanted to it and didn’t have to care), I really hated that ’15’ gallon tank. With that and the terrible highway fuel mileage, I could go father between fuel stops on my Goldwing than the YJ! A buddy and I drove it from south eastern Indiana to Red River gorge, and found ourselves regularly stopping about every 150 miles.
Gaslighting!
COTD material.
I second the motion. All in favor say Aye.
Aye-six.
(What? It’s a Jeep.)
…I don’t understand… 🙂
It means inline-six.
I suspect whoever wrote that bit assumed that petrol weighed the same as water (possibly because they’re both low-viscosity fluids).
Assuming it’s the weight of water is a safe overestimate since we’re trying illustrate that the weight is pretty negligible
Excellent David! Maybe there are more free hacks out there to find. “Use shorter spark plugs to make room for more gas! Gain 20 hp!!!”
If you used bigger spark plugs, that stuck further into the combustion chamber,you’d increase compression, which should increase fuel efficiency/power. Up until it started knocking anyway.
My cars could use more hit points.
Oops, wrong forum….
Eh, go for the Constitution increase instead of feats that just increase HP. You won’t get quite as much health but it’ll help their saving throws against rust monsters (read: the Ohio DoT) and gelatinous cubes (most Ohio pickup drivers).
Why couldn’t BMW just use the rubber hose trick? It’s a Jeep thing. They didn’t understand 😛
Ze beatings vil continue until morale improves.