Amazing the way the ambient temp. hurts mileage

welcome to the cold weather mpg blues

 

Yep, really surprised me to when I first started noticing it.
The increase in air density plays a significant role, as will increased rolling resistance.

 

I've been driving a Prius since 2005 and it still amazes me when temps stay below 60F and mpg drops.

 

The Prius mpg's is greatly impacted in a negative manner when the temps drop more than
any other vehicle I have ever owned. My 2003 VW Jetta Wagon TDI (diesel) 5-speed manual
gets 50-51 mpg in the winter and 52-54 in the summer.

Prius gets 45-48 winter (calculated of course) and 51-54 mpg in summer....

 

I suspect if you could somehow spoof higher ambient temp (fool the car computer) your mpg would go up, but maybe with consequences, like poor heater performance, or lugging engine.

 

You would still suffer from increased rolling resistance, increased drag and longer warmup times.

 

As the driving temperature drops from about 70 to 40 degrees Fahrenheit, my 2010 Prius' 16 mile commute's fuel efficiency has drop from 70-75 mpg to 60-65 mpg going downhill (down 200 feet) and from 60-65 mpg to 50-55 mpg going uphill (go up 200 feet). This is despite the Prius grills are 100% blocked, the tires are over inflated to 40 psi front and 38 psi rear, and I'm using two scangaugeII s to help me with hypermiling. The reformulated 10% ethanol 87 octane gas that I'm using seems to pucker out that more quickly in the cold

 

I also think it has a lot to do with the winter blend of gas that's in our tanks now.

 

It's not as big as you think. See Car and Driver: Mileage? No, it's Your Gallonage that Really Counts | PriusChat.

Run some gallonage calculations yourself.

Partly, but there are other factors. See Why mileage gets worse in winter | PriusChat.

 

It could be worse...I live in Edmonton Canada and with the cold weather (-10 degrees Celsius,14 degrees Fahrenheit) and heavy snow this week my "HybRED" got around 7.0 l/100km (33.6 mpg).

 

Ouch... I thought my last tank @ 45.4 mpg was bad. Worst tank ever for me was 38.

 

To the original poster:
Are you grill blocking?

Also, try waiting a bit with the heater until the car has had a little chance to warm up.

 

There is a whole sticky about grill blocking. It contains so much more information then I could ever put in this post. All I will say is... It is an absolute no brainer to do it. Costs virtually nothing and takes very little time. The thread is at the top of the fuel economy subforum.

 

This veteran's day holiday weekend has been very warm with the day time temperatures reaching back to 70 degrees Fahrenheit. Didn't need to wear a coat. Yesterday (November 11 2012), hypermiling on my Prius returned summertime fuel efficiency ( 70 mpg as estimated by ScangaugeII AVG meter ).
Wacky Winter weather. Very Strange for November in the DC Area.

 

We finally hit the 40's for our low out west. I checked my air pressures and they were off 4-6psi. I had aired the tires just three weeks ago to 42/40.

 

Yep, wild weather in our area for sure....

Saw first hand how colder weather will affect my mpg ratings in colder weather after the nice weekend....

 

None of us are immune. Cold affects all vehicles. This final winter with my previous Prius illustrates the situation well.



My new Prius is taking a hit as well. MPG on the commute to work has dropped from the low 200's to the low 100's. Isn't that horrible?

 

Did some looking at Fuelly at other cars and it seems to mirror your chart - a 15% hit... It is that at higher mpg's the differences are more pronounced..