# Increased mpg

My closest gas station (independant) sells “ethanol free” gas. Since using it exclusively I have gone from 31.6mpg to 34.66mpg. Car ('03 Nissan Sentra) starts quicker and feels peppier. Talked with station owner and his customer’s report 3-4mpg better mileage. What gives???

My cars do the same thing. E10 (gas with 10% ethanol) reduces fuel mileage by about 10%, or at least that’s been my experience over the last year. You’re lucky you can still find real gasoline. It’s almost impossible to find in my area.

I’ve never noticed any difference in start-up or engine performance with E10, but the mileage on both of my cars drops by 3-4 mpg when running on E10.

I don’t doubt that you’ll see an increase in fuel economy with straight gas. But it shouldn’t feel any peppier. If anything the E10 would make your car more responsive, since ethanol has a higher octane rating than gas.

First, I don’t think your fuel economy went from 31.6 MPG to 34.66 MPG. There is no way you could know your fuel economy that precisely. Here is why.

Let’s say your gas receipt says you bought about 8.224 gallons. (It could be between 8.2236 and 8.2244. We don’t know for sure.) According to your odometer, you traveled about 255.8 miles using that much gas. (Again, it could be between 254.76 and 255.84.) Your least precise measurement is only to one decimal place. Therefore, in this example, you only know you got about 31 MPG. Your answer can not be more precise than the data you used to calculate it. You use data that is precise as possible, but you have to drop enough decimal places from the answer until your answer isn’t more precise than your least precise data.

So, now you know you went from about 32 MPG to about 35 MPG. That fits what we know about ethanol. Ethanol, or mixes of it like E-85 (85% ethanol, 15% gasoline), will deliver fewer miles per gallon than pure gasoline. However, there are other advantages to putting a little ethanol in gas. Ethanol burns cleaner, and as we improve processes for making ethanol, the cost will go down. Furthermore, the people of Brazil have proven ethanol is a sustainable source of energy when it is done right. Unlike us, they make it using sugar cane rather than corn. So there are both advantages and disadvantages to E-10 gas.

Would be true, but they adjust the overall octane of the mixture back down to match what the all gas mixture would be. There is more energy content in gasoline than in ethanol, therefore all gas = better milage.

Perhaps the OP is using a digital MPG gauge in their car?

I don’t think the 2003 Sentra has one, but you might be right.

Higher octane doesn’t make the car peppier. Higher octane simply prevents some of the problems that come with the technology that makes a car peppier. It allows higher compression pressures without preignition.

An engine will not perform better simply due to higher octane.

Perhaps the OP is using a digital MPG gauge in their car?

Those things are notoriously INACCURATE.

If the gas doesn’t contain ethanol then what does is contain?? Last I knew the EPA required gas to contain a Oxygenator. Most use Ethanol…MTBE…I’ll take the decrease in gas mileage instead of MTBE polluting my drinking water.

Proof? The ones in my cars have been very accurate. Why wouldn’t they be?

Car And Driver did dyno testing on a circa 1999-2000 Mustang GT, a car that only requires and recommends 87 octane fuel. They dyno’d it running on both fuels. The 93 octane produced 3 more HP and 5 more ft./lbs of torque. Turns out Ford cars with the 4.6L wit the EEC-V ECU have software that can allow them to take advantage of higher octane fuel. It’s undocumented and may have been taken out in more recent models with newer firmware revisions.

I also question if the OP has the equipment to figure gas mileage down to two deciminal places. I don’t notice any change, I fiqure it is because my measuring equipment is not sensitive enough to catch the reduction, some say 10% others say 2%

My equipment consists of the gas pump that tells me how much gas and my odometer telling me how far. My accuracy is just a whole number, no tenths, and so many things affecting mpg (driving conditions,technique,temperature,) I think it is very good to get to a plus,minus 1mpg margin of error. I could be fooling myself that it is that good.

Why wouldn’t they be?

Because there’s those systems don’t measure gas usage in real time. They use an algorithm to ESTIMATE the gas usage. Mileage is accurate. I don’t have to show they don’t work…show me one that they do work. I’ve never seen one work correctly. The one on my Toyota constantly says I’m getting somewhere between 19.1 and 19.3…When I calculate it out (which is very accurate) - it comes to 21 - 22. That’s a 10% difference.

That’s a good point. After all, your odometer doesn’t know if your tires are new or worn.

I should add for the OP that if the measured numbers you use in your calculations are whole numbers, your answer will only be accurate to the tens. 256 miles / 8 gallons = about 30 MPG. The answer isn’t 32 MPG unless you know you are dealing with 256.0 and 8.0. Isn’t Physics phun?

Where do you get this mis-information? They measure gas consumption by knowing how much gas flows through the fuel injectors. They know this because they know how long the injectors are open and they know what the fuel pressure is. If they didn’t know this very accurately, they could never run the engine correctly with low emissions. Some aftermarket gauges may have to do a little guess work, but the OEM built-in ones don’t guess, they know. Perhaps your data that you are using for the calculations is faulty. Can you prove it isn’t. Have you ever truly measured what is in the tank before and after a trip? You trust the odometer for the miles traveled, but don’t trust the other gauge? You trust the gas pump, but those are often proven wrong. BTW, by law they only have to be accurate by about +/- 10%. As you might guess, they often over-measure by close to 10%. Anyway, I can’t speak to Toyota, but Ford/Lincoln/Mercury are very accurate.

I know that was the approximate time that the Mustang and Lincoln 4.6s got knock sensors. Some of the other Fords and Mercs had to wait a year or two more to get them.

Yet NH still allows up to 0.5% MTBE in gasoline. We don’t use ground water around here, but I still don’t like the idea of poisoning it. Well, some folks do, but not in my neighborhood.

What I believe was actually happening was that the system with its knock sensor was compromising for the tendency for pinging from the lower octane gasoline, so the performance was compromised. I guess it could be said that the software allowed slightly more advanced ignition timing with higher octane, but that gives the impression that it has the ability to recognize octane, which it does not.

93 octane contains no more energy than 87 octane. And there is no way for the engine’s control systems to know what octane is in the fuel lines. It’s simply protecting an engine that has been designed to take advantage of higher octane’s lesser tendency to ping from damage from the use of too low an octane.

That is what once would think. However the 4.6L in the Mustang (GT,not a cobra) only requires 87 octane. 87 octane is the recommended fuel as well. It just turned out that the ECU tuning in these cars makes provisions for higher octane fuel and can adjust timing to get some (however small) benefit from it.