Why my mpg does not match promised values?

I see we have a Nebraska corn farmer here. I said about 10% fuel economy reductions. Can you provide empirical evidence that proves that ethanol reduces vehicle emissions?

 

I said nothing about emissions and I'm not a farmer. Your comment was on fuel economy, and you have provided no math or evidence to support your claim, which math based on energy content does not appear to support.

Here is the math. Ethanol contains about 1/3 less energy per gallon than gasoline. So, the energy in a gallon of E10 compared to a gallon of E0 is:

0.9 * 1 + 0.1 * 2/3 = 0.967, or 96.7% as much energy per gallon in E10 compared to E0.

If you use E15, then 0.85 * 1 + 0.15 * 2/3 = 0.95.

 

My mileage matches the EPA promised values. I simply point out that my fuel economy is better in the summer. This year my fuel mileage is not as good because they changed the ethanol blend in Washington state last year. Supposedly they are using the same amount of ethanol year round.

 

That's not quite the same as ethanol drops mileage by 10%.

Everybody's fuel economy is better in the summer, including mine. Winter increases air density, lubricants are more viscous, etc. Plus, winter fuel blends are different for vapor emissions reasons in many states, generally with less energy content. My recent diesel VW took a huge hit in the winter (about 20%), primarily due to the winter fuel mix, but also due to winter driving conditions.

A few data points from my 2018 Prime - all on 10% ethanol fuel.

Road trip from California to Nebraska Jan 2019, highway speeds about 65-73 mph. Fills along the way with 46.1 mpg, 47.4 mpg, 57.7 mpg (some city driving on that tank), and 44.1 mpg.

Recent road trip from Nebraska to east coast, Canada, upper midwest in May 2019. The highway sections (which generally match the speed on the previous trip), 55.6 mpg, 62 mpg, 57.8 mpg, 59.4 mpg and 64 mpg.

Edit - here is what the EPA has to say on cold weather fuel economy:

Fuel Economy in Cold Weather

Fuel economy tests show that, in short-trip city driving, a conventional gasoline car's gas mileage is about 12% lower at 20°F than it would be at 77°F. It can drop as much as 22% for very short trips (3 to 4 miles).

The effect on hybrids is worse. Their fuel economy can drop about 31% to 34% under these conditions.​

 

Some folks trade the winter cold weather penalty for summer AC penalty. I prefer to start turn the system off and start rolling the windows down, when it's starting to warm up. Unless we're doing some significant highway drive. Even then, half the time, just crack the windows. Obviously not in the sub-tropic here. But hey, we were hotter than L.A. today, in Coquitlam...

Also, speaking of ethanol: the official mpg testing is done with ethanol-free gas, if I'm not mistaken? So if you drive exactly the test parameters, you'd be lucky to get within 95% or so?

 

On my recent trip, I noted almost no change in mpg when I ran A/C. On a 750 mile day, the first 1/4 was without A/C and the mileage display on the display didn't change at all when I turned on the A/C at the same speed. I didn't stop for gas at the A/C start point, so no actual tank filling data, but all the data from the dash and Hybrid Assistant showed no significant change. I was impressed how efficient the A/C is on the car.

But, like you I drive around town with the windows down, since I like lots of fresh air. Once I hit the highway, the windows go up.

Correct. They use E0 (certification gas).

 

I realize that different states use different amounts of ethanol. Washington State has a sign on the pumps that said this fuel contains up to 10% ethanol. Then they started a summer blend. Now the ethanol is basically all the same year round. So the good times of fuel economy for me are over.

 

You will be taking about a 4% hit compared to E0, with all other parameters equal.

 

You are thinking of the wrong decade, maybe even wrong century. The seasonal-only ethanol was used in the middle years of my 1986 Accord that my first Prius replaced. And even it (Honda) displayed a significant winter MPG dip before that seasonal ethanol mandate appeared. As a relative who blended fuels at a local refinery pointed out, winter gasoline is less dense and has less energy per unit volume, therefore it has lower MPG too. And this is separate from ethanol mandates.

Don't forget the wet and snowy roads, denser air, higher winds, and greater engine block heat loss, all dragging down MPG too.

Yes, see the fuel blend density issue above.

It is common knowledge that 10% is a serious exaggeration. This dyno test of many old cars found an average of 3.7% reduction:
Pure Gas ( No Ethanol ) experiment | Page 5 | PriusChat

Could you provide instructions about how to find the lifetime MPG display on a Gen3? I'm not aware that it has such.

The car that produced the displayed MPG above, was traded in 7 years ago, so is no longer available to me. My current Prius has a hitch receiver and has rolled up very many miles as a toy hauler, significantly reducing its MPG, so its lifetime MPG (if we can even find such a display) is not comparable to a car not used for such duty. While I have a lifetime fuel log for it, it isn't spreadsheeted, and I'm not going to spreadsheet it just for the sake of this thread.

 

They can use any fuel they want. The tests don't actually measure fuel volume input at all, but just exhaust outputs, then compute back to some theoretical reference fuel blend.

This century, the EPA ratings scale was pushed down significantly in 2007, and then pushed down a bit more, more recently. Those scale changes much more than offset the E10 MPG loss.

 

Why am I not surprised, lol:

 

(1) EPA doesn't 'promise' anything, and has a bold disclaimer of 'your mileage may vary'.

(2) My condolences that your cars don't exceed their EPA ratings. Starting with my '86 Accord, all of mine have exceeded their EPA ratings. Well, the 1997 Legacy didn't at first, until I learned a bit about hypermiling, then it jumped up to well above its EPA scale. And both of those cars were before the EPA 's first scale downgrade this century.

They've been allowed to use 10% ethanol year-round for a very long time. Has your particular supplier been using less?

 

My PRIUS is the only car I've owned which hasn't a measurable hit by using E10 petrol. Others took approx a 10% hit. I've got every fill logged since 1975 - and PRIUS surprised me. If there is any, it's not showing up, and may be due to the efficiency of the car making it harder to measure.

 

In 2008 they changed to a more realistic test cycle, with higher speeds, air conditioning and colder temperatures. Even so, the tests aren't representative of the driving most people do, so they still have to apply corrections. I think there was a correction in the past 5 years that applied to hybrids specifically, but can't find the reference (edit, it was in 2017).

Detailed Test Information

I've never put much emphasis on the actual EPA values, but they are helpful to compare different car models, all of which were tested under the same conditions. This shows that a Prius will get better mileage than a Camry, for example, but neither will actually get the EPA values. And then there are driver differences that don't appear in the standardized test. My wife typically gets 10% worse mileage in her Outback than I do, driving under similar conditions.

This is the EPA estimate for my 2011 VW TDI wagon - my lifetime average with that car over 80K miles was 42 mpg, and that includes the winter months where I got 36-39 mpg. The worst tank ever on that car was 34.7 mpg.

 

OK, Model Year 2008, appearing in late 2007.

'Corrections' have been around since mid-1980s-ish. Before that EPA ratings matched CAFE tests. Then in the 1980s, EPA Highway was reduced to 78% of CAFE highway, EPA City reduced to 90% of CAFE City.

But as the National 55 MPH Speed Limit was abolished, more people bought A/C, speed limits were push ever higher, drivers more blatantly ignored those limits, and manufacturers improved their testing gamesmanship, the typical gaps between EPA and real life grew ever wider, even before hybrids wrecked the test methodology. Hence the MY2008 changes.

Something clearly changed at about the same time Gen4 was released. And it also showed up in re-stated (downward) Gen3 ratings on the fueleconomy.gov figures.

My own results changed more than that after reading up on Wayne Gerdes. My prior style worked fine with my Accord, but bombed on my Legacy. Though finally getting it right on the Legacy gave a huge boost to the Accord too.

 

My 2 FORD diesels are the only ones which matched or bettered the EPA (our equivalent) l/100km rating.

 

This would have been the 2017 change. Here is what EPA shows for new and old ratings for the same car:

Compare Original and New Fuel Economy Estimates

 

My 2006 MX-5 estimates from EPA (old and new). Lifetime average 30.4 mpg, highway typically 32-33 mpg (and I don't drive this car while trying to maximize fuel economy). I can't recall any vehicle I have owned that didn't exceed the EPA estimates.

 

And Toyota used the new rating for the 2016 Prius.

 

Yes. The Gen 4 has improved fuel efficiency over the Gen 3. The Gen 3 example shows the step change due to the change in the estimating method used by EPA. Under the older method the Gen 4 would have been similarly higher.