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Also found this about fuel evaporation correlation to the temperature.



From AAA.com

Every spring gas prices seem to skyrocket to the highest prices of the year. Why does this happen? In explanation, we hear the experts say that many of the refineries are “down for maintenance while transitioning from winter-blend to summer-blend gasoline,” but what does this mean?

The difference between summer- and winter-blend gasoline involves the Reid Vapor Pressure (RVP) of the fuel. RVP is a measure of how easily the fuel evaporates at a given temperature. The more volatile a gasoline (higher RVP), the easier it evaporates.

Winter-blend fuel has a higher RVP because the fuel must be able to evaporate at low temperatures for the engine to operate properly, especially when the engine is cold. If the RVP is too low on a frigid day, the vehicle will be hard to start and once started, will run rough.

Summer-blend gasoline has a lower RVP to prevent excessive evaporation when outside temperatures rise. Reducing the volatility of summer gas decreases emissions that can contribute to unhealthy ozone and smog levels. A lower RVP also helps prevent drivability problems such as vapor lock on hot days, especially in older vehicles.

The US Environmental Protection Agency (EPA) says conventional summer-blend gasoline contains 1.7 percent more energy than winter-blend gas, which is one reason why gas mileage is slightly better in the summer. However, the summer-blend is also more expensive to produce, and that cost is passed on to the motorist.

The switch between the two fuels happens twice a year, once in the fall (to winter-blend) and again in the spring (to summer-blend). The changeover requires significant work at refineries, so oil companies schedule their maintenance for those times when they will already be “down” for the blend switches.

As a consumer, the main thing to understand is that there are real reasons for the switch from winter- to summer-blend fuel, even if it results in some pain at the pump.
 

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You may notice that your gas mileage has gone down a little bit in the past couple of months. Before we go blaming on ethanol (even though ethanol’s been in the fuel all year), you might want to consider the little-known fact that “summer blend” gas is actually different from “winter blend” gas.
What’s this? Gas isn’t the same all year round? Well no, it really isn’t.
Gasoline formulators vary the composition of gas in the hot summer months and the colder winter months, in order to meet emissions and air quality standards. This “reformulated” gas is blended in such a way that it has a lower vapor pressure in the summer and a high vapor pressure in the winter blends. This means the summer gas evaporates less and thus contributes less to the “evaporative emissions” which represent million of gallons of gasoline per year evaporated in the air. Winter gas is more volatile and evaporates more quickly, so it is ideal for it is used in the colder air of winter.
In terms of gas mileage, you get better mileage on summer blends than winter blends because the summer blend gasoline has about 2% greater energy value than winter blend. So the gas you are using now most likely has a lower energy value than the gas you used in the winter. That means a little bit lower mileage for you until the spring time, when they will reintroduce summer blend gasoline. And this is beyond mileage loss you see with ethanol being blended into both summer and winter fuels. Cars, trucks, boats and small engines, all will see the difference in mileage and fuel consumption between the seasons.
Why can’t they just use summer blend gas all year round? Summer blend gas doesn’t work as well in the cold winter months because it is less volatile and doesn’t evaporate as well. This contributes to starting problems in the winter. Hence winter blend gas is prepared to eliminate this issue.
Can you avoid the summer gas/winter gas switch? Not likely if you live in California, New England or a major city of any appreciable size.
 

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72k. On my last journey between the L.A. area and Sacramento I set the cruise control at about 2200 RPM / 72.5 mph, and seemed to get around 30 mpg, but tires might have been a bit low, and the air filter was filthy. Very little cargo and one person.

Too slow for nearly everyone, but faster than the trucks in right lane so had to do a constant dance, back and forth.
 

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Discussion Starter #46
72k. On my last journey between the L.A. area and Sacramento I set the cruise control at about 2200 RPM / 72.5 mph, and seemed to get around 30 mpg, but tires might have been a bit low, and the air filter was filthy. Very little cargo and one person.

Too slow for nearly everyone, but faster than the trucks in right lane so had to do a constant dance, back and forth.
I'd say 70ish mph is a sweet spot for the 2AZ-FE for milage. I just tend to be higher than that...
 

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I'd say 70ish mph is a sweet spot for the 2AZ-FE for milage. I just tend to be higher than that...
70 mph is not quite fast enough these days if the slow lane is around 65. The 2005 is the first with the standard 4-speed plus overdrive (5-speed), yes? The last upshift is at 45 to 50 mph on level ground. A six-speed would be better for this relatively powerful engine.
 

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Discussion Starter #48
70 mph is not quite fast enough these days if the slow lane is around 65. The 2005 is the first with the standard 4-speed plus overdrive (5-speed), yes? The last upshift is at 45 to 50 mph on level ground. A six-speed would be better for this relatively powerful engine.
A 6 speed might help with MPG but I think the 5-speed is sufficient. Any speed nowadays is not fast enough nowadays (in Wisconsin).
  • Speed Limit 65 MPH
    • Everyone does 80 MPH
  • Speed Limit 70 MPH
    • Everyone does 80 MPH
Or in the case of Illinois
  • Speed Limit 55 MPH
    • Everyone does 80 MPH
 

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A 6 speed might help with MPG but I think the 5-speed is sufficient. Any speed nowadays is not fast enough nowadays (in Wisconsin).
  • Speed Limit 65 MPH
    • Everyone does 80 MPH
  • Speed Limit 70 MPH
    • Everyone does 80 MPH
Or in the case of Illinois
  • Speed Limit 55 MPH
    • Everyone does 80 MPH
YES, I was referencing I-5 in California, where outside of built up areas the highway only has two lanes. In these sections during times of no congestion and dry weather the no 1 lane is around 80 to 85 and the no 2 lane is around 65 -- the latter is almost exclusively long distance tractor-trailers.

I will drive 80-85 in the Sacramento area if I am running a bit late, but that's around 3000 RPM so bad for mileage. Nearly everyone is going 75 or faster.
 

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Discussion Starter #50
YES, I was referencing I-5 in California, where outside of built up areas the highway only has two lanes. In these sections during times of no congestion and dry weather the no 1 lane is around 80 to 85 and the no 2 lane is around 65 -- the latter is almost exclusively long distance tractor-trailers.

I will drive 80-85 in the Sacramento area if I am running a bit late, but that's around 3000 RPM so bad for mileage. Nearly everyone is going 75 or faster.
Yep, I see no reason for anyone to go over 90 MPH. I might do 89 MPH but any higher is a waste of gas. 89 MPH is already a lot of wasted gas.
 

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2009 Camry:124k miles. I average 21 mpg since I bought the car used late 2018.

My driving is about 70/30 city/hwy where it's usually stop and go around the city. Mostly filled up at Sams Club, but now I've switched to Costco the last 4 fill ups. 87 octane. All info logged at gasbuddy.com

Pretty disappointing, but I guess that's how it is with city driving. Best I've got was 23 mpg, but that was because I drove to Palm Springs, CA and back from OC that week. I think the O2 sensor is the original, but I've never seen an issue with it (no CEL code for O2). At the current miles, I should probably replace it anyway?

I'll be changing the valve cover gasket in the coming days and an oil change. Still diagnosing a P0301 code that popped up a few days ago. Seems to only misfire on a cold start, but goes away eventually. Been swapping #1 ignition coil into a different cylinder.

Replacing VCG, because Im finding some oil on my spark plugs. Dont see any leaks in the outer area of the cover. It's a 2AZFE, so it's most likely something more internal, aka bad piston rings. Some sad times. Luckily, the oil burning isn't too bad right now.
 
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