Is NJ gas better than Massachusetts gas?

July 26, 2012 4:16 PM

New Jersey gasoline is more efficient than Massachusetts gasoline? I seem to get much better gas mileage with both my cars when they are filled up in NJ. What gives?

We live in Boston, have family in NJ, so we make the pilgrimage at least two times, sometimes three times a year. Our older car (a 2002 Mazda Tribute V-6) goes one way on almost exactly one tank of gas so I fill up usually as quick as I can when getting to one side or the other. I consistently, barring traffic (Grrrr!Thanksgiving) get 22mpg going to NJ and 24mpg going back. Over the last 10 years I chalked it up to loss of elevation and perhaps tailwind and maybe less traffic coming East. Now we have a newer car with a bigger tank and better mpg. Not only is the difference more exaggerated, but I can arrive back in MA with nearly a half tank of NJ gas which I did this week, but that's not the mystery. Also, our new car has an mpg computer and not only did I notice a big change in mpg coming home (about 4 mpg), now I'm still using the NJ gas and I'm seeing 2-4mpg better gas mileage on my short 9 mile commute to work. Being an engineer, I know exactly what my mpg is with and without Air Conditioning and it's vastly better with the NJ gas. I just know I'm going to fill up this weekend with MA gas and it's going to drop back down. More ethanol? Some other additive? We use only name brand gas (Shell, Sunoco, Gulf, etc.) from various stations. One more side-note: Even though our MA gas mpg seems lower, I found one gas station here in MA where the price is good and the mpg is even 2mpg lower still? Is there a way to dilute gasoline and sell it for a lower price? Interestingly this same lower mpg supposedly name brand station gives a discount for cash instead of a higher price for credit. Thanks in advance.

posted by Rafaelloello to home & garden (23 answers total)

Ethanol can cause this. Ethanol contains much less energy than gasoline. Most of today's gasolines contain ethanol, but most advertise they can contain "up to" a certain percentage of ethanol, so the NJ gas could simply have less, or even none at all.
posted by kindall at 4:18 PM on July 26, 2012

Gas in Mass has up to 10% ethanol, according to the google. NJ is switching to ethanol from MTBE, but maybe isn't using as much ethanol in the mix yet? Don't worry, pretty much all "gasoline" will have ethanol added soon. Thanks, corn lobby!
posted by DaveP at 4:21 PM on July 26, 2012 [2 favorites]

Ethanol blends do have less energy per gallon. This affects cars in different ways, though. Some cars take a pretty big MPG hit, while others don't. My '91 Honda saw only the slightest difference when we switched to ethanol here. (the A/C made much more of a difference) My SO's Explorer, on the other hand, dropped fully 5MPG.

Around here, there are still stations that don't sell ethanol blends. They're (mostly) far too high in price to make it worth buying the MTBE gas. Besides, MTBE leaches into drinking water like mad. Ethanol is ethanol, so even if it did get in the water, it's as if somebody spilled a bit of everclear.
posted by wierdo at 4:57 PM on July 26, 2012

In NJ you can't fill up yourself can you? Maybe the attendant is filling you up with premium.
posted by sanka at 5:05 PM on July 26, 2012

Interestingly this same lower mpg supposedly name brand station gives a discount for cash instead of a higher price for credit.

Just a side note to your side note, that probably has to do more with the franchise's credit-card processor than anything else. It's all in the wording; there's a technicality with some processors that retailers aren't allowed to charge extra to use credit, but they're allowed to provide a discount for paying with cash.
posted by limeonaire at 5:22 PM on July 26, 2012

I'm guessing your cars have a knock sensor and the octane rating of the NJ fuel is higher.

The knock sensor will retard the car's spark timing on the lower octane fuel, resulting in slightly less power and efficiency.

If the car did not have a knock sensor and the spark timing was as far advanced as it could be for the higher octane fuel, the lower octane fuel may actually damage the engine in the longer term.

Here in Australia the octane rating of a given fuel is set by law (plain old ULP is supposed to be 91, for example), that is not the case everywhere though.
posted by deadwax at 6:22 PM on July 26, 2012

Oh, I should add, if your car had no knock sensor and the spark timing was set so that it could safely run on either octane rating, you would notice no difference in efficiency between fuels.
posted by deadwax at 6:24 PM on July 26, 2012

According to this, the ethanol content makes almost literally no difference compared to MTBE gas or ETBE gas. Furthermore, since internal combustion engines are only 25-33% efficient, you can cut the difference by that amount.

I don't doubt there is a difference, but ethanol isn't it. I suspect it is an octane thing. My new car drives significantly better on high octane gas than regular.

Now, what it CAN be is poorly stored or sourced ethanol gasoline absorbing moisture and causing it to go shitty. Which it can do because of the ethanol content. I wouldn't put it past bad station owners to be watering down their gas. Depending on the state regulators, they might never get caught.
posted by gjc at 6:33 PM on July 26, 2012

We only use 87 octane in both states as that's what both cars require. In fact both manuals say there is no advantage to higher octane as the computer will just detune the engine rather than furnish more power. Sounds like maybe less ethanol in the NJ gas. I've noticed the 10% ethanol signs on the pumps up here but didn't take notice in NJ. The MA station that seemed to give 2mpg less than the other (already lower than NJ) MA stations maybe has the full boat of 10% ethanol, or maybe a little bit more? Could a station illegally top it's tanks off with a little more ethanol to increase their profit margin or would it just be too hard to obtain or properly mix? Maybe independent gas distributors could do likewise?
posted by Rafaelloello at 6:40 PM on July 26, 2012

@gjc - OTOh, maybe you're right about the octane if the MA gas has a true octane number of 85 or 86 instead of the stated 87?
posted by Rafaelloello at 6:47 PM on July 26, 2012

If the computer can detune the engine upon noticing a lower octane rating the car is fitted with a knock sensor and my comment above may apply. (Most modern cars are, I'm not so lucky on my 30 year old bomb.)

So yes, it could be that the MA fuel is not what it is supposed to be. Or the NJ fuel is better than 87 and the computer is capable of improving the tuning. The manual you mentioned implies this may not be possible though.
posted by deadwax at 7:02 PM on July 26, 2012

I have noticed the same difference in mpg on my car (1999 Volvo S70). I always use the mid grade gas. It seemed like when I filled up at one station, my mpg was better.

I have since installed Gas Cubby app on my iphone. I have made it a habit to use the one station that seems to have the better gas. Gas Cubby showed my mpg to be 24.5 almost consistently. One morning I was out of coffee, I stopped at a different station, same brand name, within 2 miles of my favorite station, filled up and recorded the new gas station (#2) on Gas Cubby. I was shocked to see the mpg had dropped to 20.1 for that particular fill up. I thought it was a fluke. Continued to fill up at my favorite station, mpg returned to 24.5. After several tankfuls, I returned to the station #2 for a fill up and recorded the information in Gas Cubby, mpg again dropped to 20.1.


I am curious about this drop of 20% mpg with station #2. You are not alone in seeing a difference in mpg depending on the station. I would never given it much thought except Gas Cubby shows the glaring difference.
posted by JujuB at 9:59 PM on July 26, 2012

You say you use several different Massachusetts gas stations; do you always use the same (one) New Jersey gas station?

Oddball thought: you know how states regulate the gas pumps to ensure we get what we're paying for, and that the pumps are indeed giving us ten gallons when they SAY they're giving ten gallons? Most states actually have an aceptable range: that 'ten gallons' might not be an EXACT ten gallons, just within a small permissable plus-or-minus margin of error --- perhaps the NJ station's pumps are on the 'plus' side of that state's margin, and you are actually getting a tiny freebie.

The test for this, of course, is to use several different NJ pumps, just as you currently use several different Mass. ones.
posted by easily confused at 4:24 AM on July 27, 2012

Ethanol has around 35% less energy per gallon than gasoline. That's not to say it isn't a good fuel, since it can be burned in a higher compression engine if the engine is designed around it. In fact, a lot of race cars use it.

Unfortunately, your car can't take advantage of that higher effective octane rating, what with being of a fixed compression ratio and probably not a direct injection engine. You'll definitely get worse mileage the more of it is blended into the fuel.
posted by pjaust at 5:58 AM on July 27, 2012

Nope. There is no consistency at all to NJ station we pick to refuel. In fact, the gas that's in the car now is from a station I had never previously visited, Shell I think. I would say about 90% of the time we fill up at the local Sunoco in MA, but before gas prices got out of hand and they reverted to the cash/credit spread we had used our local Shell quite a lot but not for the last year or so as it is significantly higher priced now.

You say you use several different Massachusetts gas stations; do you always use the same (one) New Jersey gas station?
posted by Rafaelloello at 6:15 AM on July 27, 2012

On our older car this might have been plausible, but our new car with trip computer disproves this theory, at least for our anecdotal experience. If I reset the average mpg calculation on fill up and then don't touch it until the next fill up the manual calculation (trip odometer reading/gas pump indication of gallons purchased) always matches the car computer's continuous average mpg calculation within 0.5%. The only thing I don't like about the mpg computer is that it will tell you how many miles remaining on the current tankful based on recent mpg, which is nice, but it seems to have a 2 gallon reserve. Whenever it gets down to 0 miles remaining I fill up and the car always takes ~16.5 gallons, yet the car has an 18.5 gallon tank. I understand what the manufacturer is doing, as you may not be able to use every last drop based on incline, cornering forces, etc., but I would still like it if they cut it a little closer. The low fuel light comes on, I think, with around 20-30 miles remaining, but it is really 20-30 miles and then there's 2 more gallons beyond that.

Oddball thought: you know how states regulate the gas pumps to ensure we get what we're paying for, and that the pumps are indeed giving us ten gallons when they SAY they're giving ten gallons? Most states actually have an aceptable range: that 'ten gallons' might not be an EXACT ten gallons, just within a small permissable plus-or-minus margin of error --- perhaps the NJ station's pumps are on the 'plus' side of that state's margin, and you are actually getting a tiny freebie.
posted by Rafaelloello at 6:26 AM on July 27, 2012

Is it possible you're driving more highway miles in NJ than you are in MA and that's what's contributing to your better mileage?
posted by eatcake at 6:32 AM on July 27, 2012

Most states actually have an aceptable range: that 'ten gallons' might not be an EXACT ten gallons, just within a small permissable plus-or-minus margin of error --- perhaps the NJ station's pumps are on the 'plus' side of that state's margin, and you are actually getting a tiny freebie.

That's definitely plausible. I know that my state's requirements are such that it is WAY worse for a fuel dispenser to over-charge customers, so they all err in the customer's favor.

Also, regarding octane, a higher octane fuel doesn't have more energy, but because it can be compressed more before spontaneously combusting, it can deliver more power. So what happens is that the car tries to run a more aggressive tune until it sees preignition, and then backs off. So it de-tunes for lower octane gas. What I was supposing was that NJ stations might be selling 89 octane as 87 octane, allowing the car's computer to be more efficient.
posted by gjc at 6:37 AM on July 27, 2012

I'm originally from NJ now in PA and I've noticed something like this too. In NJ my fuel range will go up to 374 on a full tank but in PA it goes around 333. Noticed it years ago and it still happens. There's just something about gas in NJ that's different from other states and it's not just not being able to pum your own gas.
posted by daninnj at 10:43 AM on July 27, 2012

And these are always different stations both states in different areas of NJ and PA. Although one Shell station in Runnemede in South Jersey got me up to 400 on my fuel range (which is btw the estimated miles on the amount of gas in the tank in case that's not clear). It's so weird.
posted by daninnj at 10:47 AM on July 27, 2012

This would happen to me when I would fill up on Nevada gas versus California RFG (pre 2006) gas. California oxygenated gas had MTBE and/or Ethanol added to it. I would use the same octane gas, but got significantly better mileage with Nevada gas, no matter where I bought it from.
posted by oneirodynia at 11:56 AM on July 27, 2012

From other sources around the 'net it seems like the sum of the anecdotal evidence is that both MTBE and Ethanol oxygenates reduce mpg. There are a few who claim it doesn't or shouldn't but nobody seems to be standing up and say their car actually runs better on oxygenated fuel. I think oxygenated used to be just a winter thing, but now it's year round I think. I believe when it was only used in the winter the denser cold air made up for some of the power loss (denser air = more air molecules in the combustion chamber = more power). Maybe NJ just has less oxygenate or a less punitive oxygenate in their blend. I couldn't find much on what the exact differences state to state are on gasoline blend. I did find some 12 year old government document where it listed Northern NJ (where we go), NY, and SW Connecticut as "Areas No Longer Implementing the Winter Oxy Program" The comments were

SIP revisions for all three states have removed the oxy fuel program as control measures from their SIPs. In SW CT, oxy fuel program was retained as a contingency measure.



This would happen to me when I would fill up on Nevada gas versus California RFG
posted by Rafaelloello at 12:36 PM on July 27, 2012

The octane/knock sensor thing makes sense to me....do your cars have turbos?
posted by snuffleupagus at 5:26 AM on August 13, 2012