A/C affect on Milage

You know you are used to driving the Prius when you are disappointed in 42 MPG.

 

That's something I've thought: no matter what your ceiling and floor is, it's never good enough, LOL. The one thing that bugs me though is the con game Toyo pulls with ever optimistic in-dash display of mileage.

 

Gasoline is delivered in the Gulf states, and then pumped north in pipelines to other points, and then trucked from there. That adds cost.

 

I thought that if you use the ECO mode when running the AC, the car trims AC use for more efficient driving. Is that the case? I usually get the car cooled down, and then hit ECO for the rest of the trip (40 mph average speeds). Would that help Summer mpg?

 

I was going to ask the same question about ECO mode. I'm pretty sure I read on priuschat before that ECO mode does drop the AC compressor and fan power by ~40%. I try to use ECO when using A/C. In my limited usage so far I've only noticed a 1 MPG drop for a 50/50 highway/backroad commute, temps in the mid 80's and humid, AC set to 72

 

I agree. OTOH, I have never owned a vehicle that was completely accurate.

I have tried to understand why there is a difference. I bought gas today and both the calculated and indicated were EXACTLY the same. That does not occur often. On a recent trip, it varied from as much as 2.2 mpg. Historically, there has always been a few percentage points difference. You would think that Toyota could tweek the computer and cause the gauge to read correct. But, there must be more to the issue than a simple computer adjustment.

Personally, I am convinved the gas pump is the cause of some variation. The densitity of the gas, depending on the tempwerature, is an issue we are told. And, no doubt, we fill the tank to slightly different levels of "full" with each filling.

Is the difference constant, and the variation depends on how much fuel is added? Not sure. Would it read the same percentage difference if you added a gallon vs 10 gallons? I could check, but have not.

 

It's been hot past few days and my MPGs did go down to 47mpg from 52mpg. I've been blasting my A/C though. I'm impressed. Plus, I rarely do ECO mode because I find it dangerously unresponsive during my highway travel.

 

Indeed, I have found that to be the case. In A/C Auto mode, entering the ECO driving mode cuts the a/c fan speed in half. I do not know what effect it has on the compressor, if any.

Ed