Wow - ambient external temperature REALLY matters for MPG

Are you sure about that??

 

Southern California Temp has been rising the past week from 70-85, so does my MPG, I average was around 77.5MPG since March, now past few days has been 79.3 to 79.5MPG. Ambient temp does have an impact on the MPG for sure. Silver 2016 Four Touring.

 

Up to near 90 degrees in the next 4 days. What is Winter???!

 

It's suddenly become very cold in London, with daytime temps down to 41F/5C.

It's now drinking fuel compared to the summer months, especially for shorter trips (<3 miles) from cold.

 

Thanks for the report, Raspy. I very curious to see how my car performs in colder weather.

 

It hit me yesterday, as after a 1.8 mile drive with a cold engine, when I switched the car off, the MFD reported fuel economy of 32.8mpg (which works out as 27.3 US mpg)

 

...My odo is about 3% high...

When I did my last fill-up, my hand calculated mpg was only 9/10 lower than the computer displayed mpg.
(No, I'm not making that up. I don't "fudge numbers" like some Fuelly guys do.)

And if I had pulled the nozzle out at the first click-off, my calculated mpg would have been better than what the display said. But I always squeeze in an extra gallon of gas. So I don't understand all the negative comments that the computer display is getting. That has not been my experience.

The biggest difference I ever had between the displayed, and hand calculated, was only 2 mpg. And that was only on the very first tank of gas when the car was new. Since then, I don't see any significant difference. I'll bet you a large pizza!

 

Yes, other people have reported similar results. But I think those very short trips are misleading? If you had driven 10 miles, the mpg would probably be normal. Are you looking at the "From-the-Flag" mpg indicator?
I find that one to be the most misleading.

I only look at my "Trip-A" indicator. And it's always stuck on 62 mpg.

 

I went to get petrol. Than back home. And this is my MPG.

 

@Coast Cruiser I think we're just misunderstanding each other: "odo", short for odometer, is the car's total miles (or km) travelled since built. Nothing to do with mpg.

And yeah, from reports here, the 4th gen's mpg display appears to be more accurate. 3'rd gen is 7.5% optimistic in my experience. 4th gen is 3~5%?

 

Am I stating the obvious in saying that Prii use more fuel in cold weather in keeping the cabin warm. I leave the heater turned OFF for very short winter journeys and as a result get FAR better mpg than with the heater on. This is with a Gen2.

I guess that the mpg hit will vary according to use of eco mode or not and requested cabin temp, and the hit is prob less in more recent gens but the car is still likely to run the ICE more in cold weather in order to heat the cabin isn't it, especially when stationary?

Posted via the PriusChat mobile app.

 

The car's computer monitors ambient temperatures, and (I strongly suspect) changes warm-up protocol as temperatures drop, running the engine more and longer. And I know for sure the cabin temp you set makes a difference: I've been sitting at red light with partially warmed car and can consistently turn the engine on/off by just raising/lowering the cabin temp. The threshold is somewhere around 21.5C (70F).

Our's is third gen, but I'd think this is applicable to other gen's too.

 

Yeah, I meant the MPG display... not the ODO.

And as everyone knows by now, I only check my MPG after I've gone thru a full tank. I'm old school. The only thing I look at is the little Trip-A window. (If the day ever comes, when I start checking my MPG after driving only 2 miles... throw me in the Funny Farm!! )

And when it's cold, I want some heat! And when it's HOT (90 today) I'm going to blast the AC. I'm not going to squabble over a little tiny loss in MPG. I wouldn't care if the miles per gallon dropped down to 50! I'm still good with that! Where else am I going to get 50 MPG????? (And have a nice COOL car. )

For corn's sake! I'm not going to pinch pennies just because I'm driving a Prius.
And I got another gripe... Where is that headlight thread… I can't believe all the Pre-Eyes I saw that didn't have their headlights on in a heavy fog!!!! Are they trying to save five cents or something!? Heaven help us.

 

I was looking at one of the two small screens in the centre that always reports mpg for the current journey a few seconds after you switch the engine off.

Posted via the PriusChat mobile app.

 

Your decision if you want heat over mpg, of course. But on what evidence do you say that turning off the heater would be a "little tiny" improvement? IMHO the degree of difference depends on the length of the journey as well as outside temp and inside temp setting, so the difference will vary greatly for different drivers at different times. For us the difference is not tiny, it's very marked.

Posted via the PriusChat mobile app.

 

On my 2017 I have found that the fan speed of the climate control makes a big difference in MPG. The Eco mode does not appear to adjust the speed automatically.

 

My experience is that summer-time A/C use and winter-time Heater use both reduce fuel economy quite abit, with mild spring / fall mileage being highest because neither A/C nor Heater are being used.

 

I guess I'm strange. (No surprise, right? ) Not the "typical" Prius driver.

Comfort (and safety) comes first, not MPG.

Lights on, always. And I'm going to run the heater or the air-conditioning as much as I please.
I bought a Prius so that I would not have to be concerned with gas mileage. Truthfully, I rarely even think about it! Anything over 40 mpg is great! I'm not going to become obsessed, or paranoid, or start tracking every last ounce of gas. No offense to anyone, but some people really take it to an extreme.

I already knew that a Prius gets great gas mileage. I find no reason to keep tracking it or charting it every day. Or every week. I guess for some people it's a hobby? To each his or her own. I only look at my MPG once a month, (or every other month) when I fill up. That's about it. And I am very blessed, and thankful, that I can buy gas anytime I need it, without financial worry.

It's kind of funny, really. People waste so much money in other parts of their lives, but yet they are concerned about using a couple more gallons of gas by turning on the lights, or their heater, or the AC!?

My Prius is great. Even when the seat is sinking.... I don't analyze it, I just drive it.