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.
In the EU the Mercedes C-class which was introduced around 2013 had a very small gas tank, approx 40 litres, where 60+ liter would be more normal for this size of car. It had shrunk to save weight, which helped reduce the gas consumption during official NEDC testing (at that time). During testing the tank had to be filled to 75%. The results from testing would determine how much tax you had to pay in several countries in the EU, so a smaller tank meant a lower selling price. A bigger gas tank was an option however, and one that was either very cheap or even free in some countries.
In my old pre-dieselgate MK3 TDi, i removed the filler vent so I could fill the tank and neck almost to the top. It seems silly, but when the car got 49MPG and I had a 650 mile commute each week, that extra bit added nearly 50 miles.
I don’t know if it’s been asked already, but are you still in touch with anyone in the engineering department at Jeep, David Tracy? I would think this would be a pretty easy question to answer. I’m sure AMC did most of the R&D on the YJ since Chrysler didn’t take over until 87, but someone there may still know. Either way, great write-up and I’d love to have more capacity in my Gladiator fuel tank.
He worked for Chrysler, specifically on Jeep vehicles. He’s more likely to know someone than anyone else, and I’m sure if he did, he would have.
So my YJ’s fuel gauge always reads “Full”, i just fill up every 100 miles. I’ll have to check if this mod has been done, it was heavily built and taken back to “stock” once before. Maybe i can fill up every 120 miles!!
I learned about this particular quirk a few months after owning my first 4-cylinder YJ. They must have used the same fuel gauge as well; on a full tank the gauge never went past the 3/4 full mark and I thought this was just due to the age. On my current YJ with the full 20 gallon capacity, the needle does go all the way to “F.”
Last two generations of the EcoCruze had this same vent stunt to cut their fuel tanks by about 3 gallons.
They also ditched the spare tires on these models, suggesting EPA weight class antics.
My dad told me a story of an oldsmobile or some GM product he had from the 60s/70s that was a lower spec model, and it had a blockoff plate on the dash where you could have optioned a clock. He removed the blockoff plate and discovered… a clock.
Corporate is so dumb.
I had a Mk1 Mazda3 in the mid-level Touring trim. The higher “Grand Touring” trim had a trip computer/instant MPG display in the multi-display that was part of the radio. Somebody figured out that if you push buttons in a certain sequence it “unlocks” the MPG feature. (I’m sure there’s tons of stories like this for different cars).
Just wait until someone removes the headliner in their stripper Model 3 and discovers it had a glass roof all along. 😉
Just wait till they peel off paint protection film they paid Tesla to install and find out there is no paint underneath it on Cybertruck
Part of this is that spilling gasoline is one of “the worst sins in the world” according to the EPA. Putting HCs into the air. It’s OK if one person does it, but 300 million people spilling a couple ounces every week or so? That adds up.
I still try to fill to the top of the neck. It’s not easy, as I have to wait for the gas to settle down before pumping another 0.1 gal. a good 20 more times.
Some new way of determining when a tank is full needs to be created. This rubber hose thing needs to be placed up someone’s nose, to quote a great perspiring swine.
Why do you fill it to the top of the neck? Seems like a huge waste of time and effort.
It’s about an extra minute, and I have the time, and the effort is minimal since I’ve been doing it a long time and am an expert with my car on it.
And, it’s more about getting to a round gallon number, so I can do the MPG in my head.
For a few years the XJ came with the 15 gallon tank, which had the same “mod” to change it to a 20 gallon.
My 1985 Ford LTD accomplishes the same thing by having a miscalibrated fuel level sender. When the tank is full the gauge shows 7/8 full, so when it reads empty I actually have a full 6 gallons, or 1/3 tank, left remaining. Better than the opposite I guess.
Could be worse… was towing the Lemons car to CO using my friend’s wife’s Silverado and ran out of gas while it was still displaying 21 miles to empty. Fortunately the gas station was downhill and was able to coast into the gas station’s lot, but not quite far enough to reach a pump. (only got into this situation because the only gas station at the previous exit 25 miles ago was closed)
Yep, precisely why I said my situation is better than the opposite.
And on the topic of Lemons and DTE displays, one time I raced a Lincoln Town Car limo in Lemons and despite the DTE display showing 10 miles I ran out of gas on track and had to be towed in. That was also the same race where the owner of the limo told me I could put the cruise control at 35 and make nearly the entire lap without touching the brakes. I took his word for that.
Delmar (NHRN) must be limiting your sleep 🙂
The engineers were just mad with power after figuring out how to make rectangular headlights hold a round amount of light. The tank was next on the list.