Temperature and Fuel Economy
 

Lest anyone still doubt the affect cold temperatures have on mileage....

I was going back through some mileage data from my morning commute. Here is a snapshot of some of my best and worst.

All trips were 10.3 miles over the same route at the same time using the same driving techniques on my morning commute. The primary difference was temperature, and of course summer blended fuel vs. winter.

1st set: Mid July, average temperature for 5 trips = 72 deg. F. Average mpg = 72.2.

2nd set: Mid January, average temperature for 5 trips = 14.2 deg. F. Average mpg = 45.8.

Spring, we await thee.... :)

Re: my temperature hit
 

I have a best tank of 33.5mpg in August and worst tank of 25.1 in January.

On my 9.6 mile daily commute I'm typically 35-36 at best summer and 23-24 at worst winter conditions.

:cry:

Re: my temperature hit
 

Darn, that's a stark set of numbers you have there. Hard to believe it's temperature alone- you had to be running the heat and defrost, for instance, in winter. Higher winds, too, maybe? But yeah, I'm with you on the 'wishing-for-spring' idea. :)

Re: my temperature hit
 

Leah,
Yes, you are right that one variable I chose not to control was the heater fan. I don't own enough warm clothes to do that. But never the defroster. "A/C OFF" is displayed whenever possible! If I needed to use the defrost, I would have discounted that data. Luckily I have a garage, so I seldom need defrost. And my data is only for my trip to work - when the car has been in the garage all night and isn't frosted over. I did not include any data in my trip home because traffic and conditions are just too variable, and I can't use the heater at work anyway. You are correct, there are other variables that are difficult to control, like potentially more wind in the winter months. I tried to control the lack of autostop in the colder months by doing a FAS at stoplights whenever practical.

Re: my temperature hit
 

Has anyone with access to the database made a plot of fuel economy vs. self-reported temperature for individual vehicle models?

Re: my temperature hit
 

Usually we do such charts for our own performance or our own model vehicles. The steps are fairly simple:

1. Identify vehicles in model that have significant numbers of samples
2. Cut-and-paste multiple vehicle data into a spreadsheet
3. Calculate averages for every 10(F) range and plot

This would be an excellent 'second posting' and introduction to GH.

I'm testing some modifications to improve my cold weather performance so I've made this chart:
http://hiwaay.net/~bzwilson/prius/pri_temp_30.jpg

Bob Wilson

Re: my temperature hit
 

I commute in a Prius II 1 hour each way (Baltimore-DC), mostly highway (~70 mph), so warmup time has less impact on my overall mileage numbers. Given that, I've been seening an 8-10% drop in fuel economy when the outside temperature drops from 30 F to 15 F. Yikes! Total drop is about 20% vs. 70 F. That's with the heater set at 65-66 F, no defroster.

I keep thinking about trying the cardboard in front of the radiator idea, but I assume that if it had a significant impact then Toyota would have engineered something into the car. But maybe its still worth trying....

-Terence

Re: my temperature hit
 

Alas, my Prius II, Touring Edition seems to suffer the same winter blues as the others posting here. I, however, do not have any summer weather for comparative purposes. Let me point out that here we have a winter blened fuel that contains Ethanol (!) and other additives. If you have been following the news on ethanol laced/based fuels, you know that ethanol cuts a car's MPG by about 15%. As ours is a winter, only, blend, I surmise that it contributes to the lower mileage along with the chilling effect of cold weather.

Now, add to the above the physics part ... when things such as gasoline get cold they contract. Thus one gallon of gas at 55 degrees (in ground, storage tank temperature) will be less than one gallon when chilled to 32 degrees or so. This too helps damper gas mileage.

I am sure there are other factors, but these two things have not been cited on this thread heretofore.

Re: my temperature hit
 

I noticed a large difference from Summer to Winter also. In the winter I use very little heat and in the summer I did not turn on the A/C until I was on the highway (about 1 mile) because it seemed to drain the battery.

I noticed a much smaller difference from Summer to Winter in my HCHI then my HCHII. That being said, in the summer I get much better mileage in the HCHII then I did in the HCHI.

I drive 25 miles on the highway and park in a garage in the evening.

Re: my temperature hit
 

No, but my data over at CleanMPG does that for me already. It may be a bit hard to understand at first, but it's neat to see once you get used to it.

http://www.cleanmpg.com/garage/images/cha235.png