Realistic EPA mileage ratings?
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From: CALIFORNIA
Realistic EPA mileage ratings?
Reviewing postings in various ClubLexus forums, the general consensus and physics suggests 100% gasoline provides better MPG over gasahol due to higher heat (BTU) content (same octane)
New car window stickers provide EPA mileage ratings .....
My question is whether auto manufacturers EPA compliance ratings reflect MPG using 100% gasoline or gasahol (10%)?
Anyone know definitively EPA guidelines with supporting documentation??
Thanks.
New car window stickers provide EPA mileage ratings .....
My question is whether auto manufacturers EPA compliance ratings reflect MPG using 100% gasoline or gasahol (10%)?
Anyone know definitively EPA guidelines with supporting documentation??
Thanks.
Thread Starter
Pole Position
Joined: Nov 2014
Posts: 3,254
Likes: 418
From: CALIFORNIA
Instructor
Joined: Nov 2006
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From: FL
Could you imagine if manufacturers had to use E85 for their EPA testing? That would yield some atrocious numbers.
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5. When I buy gas at the pump, it typically contains about 10% ethanol and other additives. Does EPA use a gasoline-ethanol blend for fuel economy testing?
No, EPA’s test fuel does not currently contain any ethanol or other oxygenates. However, EPA does account for the impact of low-level ethanol blends in our fuel economy estimates. Ethanol has a lower energy density than gasoline—about 1/3 less energy per gallon. That means a car operating on 10% ethanol would require about 3% more fuel to travel one mile than a car operating on gasoline and thus have about 3% lower fuel economy. EPA currently reduces all fuel economy test values by about 10% to account for ethanol in gasoline and other factors such as wind, hills, and road conditions. Later this decade, EPA is phasing in a requirement to change our federal emissions test fuel to include 10% ethanol by volume. Information about this change is available at: epa.gov/otaq/tier3.htm.
https://nepis.epa.gov/Exe/ZyPDF.cgi/...y=P100IENB.PDF
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From: Virginia/D.C. suburbs
While it is true that ethanol has much less energy content than gasoline (requiring larger tanks for vehicles with high concentrations of ethanol to gasoline to attain the same cruising range), it really doesn't make much of a difference at the typical E10 (10% ethanol) concentrations sold at American pumps. By my math, it comes out to only about a 3% difference in overall mileage from pure gasoline. Now, for blends like the E85 (85% ethanol) that is produced in the Midwest (many GM and Chrysler engines can run on anything from 0 to E85)...that, of course, will be a different story.
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If one drives sensibly on the Interstates, my real-world experience is that the Highway ratings are pretty accurate......even underestimated in some cases, as I sometimes do even better. However, in real-world stop-and-go driving, I agree......most of the City figures are overrated by about 2-3 MPG. And, keep in mind that, in general, all else equal, the lower the temperature, the lower the gas mileage. EPA tests are usually run at warmer temperatures.
Lead Lap
Joined: Apr 2002
Posts: 4,892
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From: Virginia
EPA is updating its method for calculating the fuel economy shown on new-car window stickers starting with the 2017 model year.
EPA periodically updates its methodology to account for changes in vehicle technologies, driver behavior, and/or driving conditions. The 2008 changes (see below) were broad revisions to the entire methodology that affected every vehicle.
The 2017 change updates some of the calculations used to estimate fuel economy. The new calculations are based on test data from model year 2011–2016 vehicles. So, they better reflect today's vehicle fleet of more fuel-efficient vehicles and advanced technologies such as hybrids and turbocharged engines.
Most vehicles are not affected by the new calculations. Some fuel economy estimates will decrease by 1 mpg, and a small number may be 2 mpg lower.
EPA periodically updates its methodology to account for changes in vehicle technologies, driver behavior, and/or driving conditions. The 2008 changes (see below) were broad revisions to the entire methodology that affected every vehicle.
The 2017 change updates some of the calculations used to estimate fuel economy. The new calculations are based on test data from model year 2011–2016 vehicles. So, they better reflect today's vehicle fleet of more fuel-efficient vehicles and advanced technologies such as hybrids and turbocharged engines.
Most vehicles are not affected by the new calculations. Some fuel economy estimates will decrease by 1 mpg, and a small number may be 2 mpg lower.
Instructor
Joined: Oct 2016
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From: Oregon
I would also assume that the EPA tests are done with a fully-warm engine. With hybrids the numbers can be significantly lower.
My RX450h hybrid gets mileage in the high 20's--but only once the engine has warmed up. If, instead, my day consists of multiple 5-minute trips, the mileage average is more like 16mpg. The computer needs a warm engine before it can work its magic, and also the climate control system demands hot coolant for the heater in the winter. So the engine keeps running for the first 5 minutes whether the computer "needs" it for locomotion or not.
My RX450h hybrid gets mileage in the high 20's--but only once the engine has warmed up. If, instead, my day consists of multiple 5-minute trips, the mileage average is more like 16mpg. The computer needs a warm engine before it can work its magic, and also the climate control system demands hot coolant for the heater in the winter. So the engine keeps running for the first 5 minutes whether the computer "needs" it for locomotion or not.
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