Impact of temperature on fuel efficiency (math nerds unite!)

In Washington state whether or not it's a summer blend or winter blend of ethanol. Fuel economy goes up about 9-10% April 1st and goes down about 9-10% November 1st.

With that said I get 53-54mpg in winter and 56-59mpg during summer driving. I keep my AC at 67-70 running all the time on eco mode. Usually my summer mpg is 58 but I listed as low as 56mpg because I have a led foot sometimes.

 

In the link that you provided I found an EPA document which lists only eight cities that are still on a winter oxygenated fuel program: Albuquerque, El Paso, Las Vegas, Los Angeles, Missoula, Phoenix, Reno, and Tucson. Followed by a very long list of cities that by year 2000 had switched to "contingency" which I assume means they could still do it as needed if carbon monoxide levels rose above a certain amount.

Interestingly in 1994 Minnesota switched to year-round oxygenated fuel.

The document was from 2008 but it's on the EPA website so presumably there have been no changes since then.

 

In my Gen 2, MPG rose with temps up to about 85 F. Beyond 95 F I could see under hood temps rise much higher than external air.

My v does not have the issue where under hood Temps climb rapidly, but does lose efficiency when A/C gets to be full blast.

 

I believe that EPA info is all out-dated re: Oxygenates

Where we are now is:
the Bush Admin/Democratic Congress banned MTBE and required ethanol-only around 2006.
Also they passed the Renewable Fuels Act which mandated quotas to >10% ethanol for all areas (ramp up started...took some time to hit the final levels we are at now).

Of course, >10% ethanol was over the "blend wall" (auto manufactures design guides) so there was a big controversy whether Congress meant it had to go >10% or just up to the 10% limit. After some bitter fights with the Ethanol Lobby who insisted Congress intended over 10% ethanol, Obama's EPA (reluctantly) decided to hold at 10% everywhere.

This was just a few years ago that the Congress mandated levels of ethanol exceeded reality (>10%) which happened because gasoline demand is lower than Congress anticipated in 2006. The fact that gasoline demand leveled off meant less pounds of ethanol than Congress originally had in mind to mandate, assuming straight line high growth of gasoline demand from 2006.

In summary (I believe) we now in USA have in general 10% ethanol all areas, all the time, all grades. There are some minor deviations, in that small oil companies have waivers, also big oil companies can sell E0 if they want to pay the fee (RIN credits). Also RFG areas are mandated must be exactly 10%, so that is the highest priority, whereas you will notice more variations in non-RFG areas including E0 availability. I figure at least 50% of Prius owners are in RFG areas (Ca. itself is about 30% of Prii).

 

I have no major problem with that Washington State observation.
As a rule of thumb, gasoline can vary by 7% in energy content (7% MPG).

Those of us living in Reformulated Gasoline (RFG) areas will see the lowest MPG because RFG is basically a low energy content version of gasoline meant to reduce emissions (by having lower "aromatics"/toluene etc).

Washington State is *not* an RFG area, so the gasoline suppliers potentially have the opportunity to give you more "aromatics" in winter - why they would do that, I do not know, just some local supply characteristic- is just theoretically possible . Also, because (above) the priority for ethanol supply is to make sure the RFG areas get their full 10% ethanol all the time, Wash State could possibly have less ethanol supply than needed to get you up to the full 10% in winter. I'd be quite sure the Ethanol Lobby is working as hard as possible to get you Washingtonians 10% ethanol all the time.

PS- "Lead" foot as in Pb

 

Darn it, I was math minor in college, but I don't remember a thing I learned in college math class. lol

 

You want more aromatics in winter to make it easier to start, and less in summer to reduce vapor lock.

And then the Government steps in.

"Vapor lock is a problem that mostly affects gasoline-fueled internal combustion engines.

It occurs when the liquid fuel changes state from liquid to gas while still in the fuel delivery system. This disrupts the operation of the fuel pump, causing loss of feed pressure to the carburetor or fuel injection system, resulting in transient loss of power or complete stalling. Restarting the engine from this state may be difficult.

The fuel can vaporize due to being heated by the engine, by the local climate or due to a lower boiling point at high altitude. In regions where fuels with higher volatility are used during the winter to improve engine startup, continued use of the specialized fuels during the summer can cause vapor lock to occur more readily." - Wikipedia

 

Now do a graph for mpg vs. tire pressure.

 

G'day,

This is my feeling when mostly city/urban driving.
I'm noticing now it's winter, the petrol engine kicks in more and takes a bit longer to kick out in the morning after starting. I imagine that it uses more fuel in winter just to keep it at operating temperature, even if the car is running mostly on the battery.

And the very low R value (original post) means the given correlation equation is not particularly good.

Still fun, though.

David S.

 

Variations in temperature, air density, speed, tire pressure, tread pattern, fuel energy content, etc... Wonder if Toyota did all of this when designing the car? They should have a Nerd page on the website and share with us!

 

Another "etc" could be "new vs worn tyres" - I guess lighter, but they grip different but mostly, the rolling circumference is changed.