Today hot weather = increased mpg. Why?

probably because the engine is always at operating temp and doesn't have to warm up much.

 

It's a great thing, the car gets to full hybrid mode more quickly with the engine heating up more quickly, and it really takes advantage of everything it's got. I had to stop in somewhere for a half hour today, when I left I was in full hybrid mode (stage 4) by the time I left the parking lot

 

Also in hot weather the gasoline engine will run more lean, not as much fuel is used.



Steve

 

And warm air is less dense (especially warm moist air), so driving through it is easier.

 

Very strange. When I first received my 2011 Prius III in April, I was consistently getting 45-47 mpg doing local driving (north Atlanta suburbs are very hilly). Now that it's gotten much warmer (consistently in he 90's) I am getting only 37-40 mpg doing the same driving.

 

Also tires roll easier.. higher pressure and less flex loss

 

Tony, you have a good point. Although I've always used the AC since I purchased the car, it is definitely working much harder in the heat. Although I've never seen the battery display drop below two bars, the engine probably kicks on more often, especially when sitting at these infamous Atlanta long traffic lights. Thanks.

 

Use the ECO button and turn up the temperature. I found out that I could barely tell the difference between 75-77 degrees because just removing some of the humidity is all that matters.

 

With all 3 generations of Prius, I've observed increased MPG from higher humidity. That includes moister air during the winter too, not just summer. It helps with the outcome of combustion, contributing to a bit more oomph than usual with the same amount of fuel due to the water expansion.
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I tried using ECO for a few weeks when I first got the car. I don't care for it. I like more responsiveness when pressing the accelerator. ECO feels like a stepping on a sea sponge.

 

Not after you put in K&N filter )

 

I agree, so I usually keep it in normal mode and when I'm going to be at cruising speed for a while (highway driving), I'll enable ECO mode, primarily to lower the A/C power usage.

 

I decided not to try the K&N route, as the vast majority of posts on this forum seem to say that it provides little or no additional benefit with the Prius.

 

How does it get more lean? Shouldn't the emission control system keep it fixed to the standard 14.7 ratio?

In a standard Otto cycle engine, the hotter intake air will have lower density, which leads to less intake vacuum / less pumping loss / less air mass consumed, therefore less fuel mass also. But this should happen without leaning out the ratio.

 

If a WB sensor is used, as is supposedly the case in the 1st gen Insight, bursts at an A/F of 22 can be possible before the CATs require an A/F of <14.7 to prevent induced imolation.
From postings it seems as if the GenII Pri uses a WB type. Time to break out the WB Innovate System and run some tests.

 

Not true, hot weather richens the full mixture. Hot air is less dense which slightly changes the fuel ratio. That's why racecars always run slower in the heat. On a Prius it's the other stated reasons.

 

Remember the hot air intake for winter?

 

That's to prevent carburetor (and some injection systems) icing.