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

Re: my temperature hit
 

Pravus Prime- yep, the dotted and solid lines track pretty darn well. Some sort of relatively direct relationship between temperature and FE is indicated. I love data! Data is great. Thanks for sharing.

Re: my temperature hit
 

Okay I'm going to try and see if I can get an image in here successfully... if it shows up this is a chart of my FE vs. mean average temp per fillup over the life of the vehicle. It's amazing how closely the lines track each other.

https://www.greenhybrid.com/share/files/6/4/6/7/feh.jpg

Re: my temperature hit
 

Wow! One thing I notice about this (all the data so far) is that not only does temperature track FE really well, but as time goes on, it gets closer and closer to an exact match. There's definitely a break-in period, where either the car is responding to battery break-in, or the driver is getting used to driving a hybrid and perfecting the technique of getting the most out of the car. Once those techniques are learned or the battery has settled down, the only 'limiting' factor on your FE seems to be the temperature. It's really remarkable.

Re: my temperature hit
 

Brady,

Your Mileage vs temperature chart looks quite similar to mine. I also used mean ambient temperatures for each tank and I am also in the Chicago area so the temperature chart is the same.

My Highlander Hybrid takes a big hit with low temperatures. The temperature/MPG correlation is very strong.

http://i148.photobucket.com/albums/s...emperature.jpg

Re: my temperature hit
 

That's great Don! Yours is a lot less erratic in the beginning than mine. As I was learning with the vehicle I was trying a lot of different techniques.

Do you use the weatherunderground almanac thing for your temperatures?

My temperature and seasonal mpg observations
 

It is great to see the data that has been gathered here. The EPA study (www.epa.gov/otaq/rfgecon.htm) that was referenced suggested that about a 20% reduction in mpg is associated with the winter due to temperature, engine warmup, and gasoline mix . While my reported temperatures have been best guesses for the driving period for each tank refill, I see similar results across 82 tanks (39,000 miles) of gas over two years in my 2005 Honda Hybrid Civic. In terms of outside temperature - below 50 oF takes a heavy toll. Above 90 oF I start touching the air conditioning so I loose the highest mpg opportunities. The second graph shows the seasonal effect. I've encoded the dates over the 2 years in fractional months. The whole number is the month number and the fractional part is the day of the month. I multiply the day of the month by 0.0322 to make it a decimal fraction of a month: thus January 1 is "1.03" and December 31 is "12.998" Obviously the temperatures vary by date but the striking change between April (4) and May (5) suggests to me a gasoline mixture change. There is considerable variability in mpg associated with other factors such as rain, snow, high speed highway driving, and occasional driving by family members who have not perfected efficient driving skills.

http://www.quine.org/07car-hybrid-plot-temp.jpg

http://www.quine.org/07car-hybrid-plot-date.jpg

Re: my temperature hit
 

Hi folks,

This is what mine looks like using excel trendlines to smooth the data:
http://hiwaay.net/~bzwilson/prius/pri_mpg_temp_010.jpg
It includes my 'learning curve' miles and picking up the car 800 miles away. Folks who started recording their data when the temperatures are increasing should use a 5th degree polynomial to keep the curves smooth.

Bob Wilson

Re: my temperature hit
 

Looks like from the graphs above that you tend to get about 1 mpg FE for every 10F warmer day.....

So my Dodge Caravan could get 50mpg at about 365F :)

2 years of data...
 

I now have 2 years of pretty good data for my Ford Escape Hybrid that I bought in April of 2005. I maintain a log for all my vehicles I have owned. The hybrid has the AWD version. Driving conditions are maybe 50% highway, 50% non-highway. Total miles driven at this time is 23,000.

Average of MPG
Month MPG
1 27.56958549
2 25.43849162
3 27.86853047
4 29.21435715
5 30.41799845
6 29.28584328
7 29.90469162
8 31.55449697
9 32.77215671
10 30.76233456
11 29.09110949
12 26.26916832

If you overlay the MPG with average temperature there is a near identical fit. The weather is Colorado near Denver. I would be curious to know what San Diego data looks like then maybe Alaska.

Re: 2 years of data...
 

That's great, but let's move this into the "Weather and FE" discussing thread, shall we?

Let's also rename the thread to make it easier for others to find.

Re: Temperature and Fuel Economy
 

Yes, ther certainly seems to be a relationship between FE and temp. An engineer friend is wondering if perhaps preheating intake air might improve things. My thought was to tap off the radiator, run hot coolant through a coil of copper tube (or motorcycle oil cooler) in the preexisting or modified air intake. The Ford Escape Hybrid does have a temperature sensor that fires up the engine to keep it warm and in cooler climes where the engine block would cool more quickly. I am not certaing which is more important, air temp in the intake or cold weather chilling the engine block.

Re: Temperature and Fuel Economy
 

There is another approach some of the Prius folks have been investigating:

http://hiwaay.net/%7Ebzwilson/prius/pri_temp_20.jpg

This works by letting the ICE autoshutdown even before it reaches 70C. This stretches out the warm-up and avoids running the ICE just for warm-up. For the technical details:
http://hiwaay.net/~bzwilson/prius/pri_temp.html

Bob Wilson

Re: Temperature and Fuel Economy
 

I admit to being confused by these results, but some have brought up other factors, such as the winter fuel mix, wind, snow or rain to plow through, etc. But it seems to me that if ALL other conditions EXCEPT for the temperature are the same, that an engine should get BETTER mpg in COLD AIR, since it is DENSER. Small airplanes sure perform better in cold air, as hot air makes for a higher "density altitude", resulting in poorer engine performance and less lift for the wings (this from a 30 year pilot)

Re: Temperature and Fuel Economy
 

After the engine is warmed up, cold air is fine although a little denser. Since lift is a function of air density, the lift improves significantly along with the higher engine output. However, in a car, lift is static, from the tires, so drag is a little higher. But these are minor effects compared with the task of keeping the ICE coolant above 70C.

The real problem is the control computers are trying to keep the ICE above 70C. The ICE is in a compartment meant to cool it. Even with a radiator block, significant heat loss occurs in cold weather. Meanwhile, the heater is also trying to keep the cabin warm by tapping the coolant, further cooling the vehicle. So the problem is in cold weather, the ICE will sometimes be run just to keep the coolant above 70C, actually 60C is the lower limit once 70C has been reached.

What is nuts is the exhaust pipe is still throwing away 1/3d of the heat energy. The problem is finding a working fluid or system that can handle the temperature ranges.

Bob Wilson

Re: Temperature and Fuel Economy
 

Performance in terms of power does come with denser air, but that's only because of more fuel, the mpg won't go up with more fuel.

Re: Temperature and Fuel Economy
 

I do use many "hypermiler" tips and tricks to get up to 53 MPG tanks in a 4,000 pound SUV... but many people contribute my fantastic results to the thinner ( less dense ) air of Colorado.

When there is less oxygen per cubic ft, it requires less fuel per cubic foot.
At the cost of horsepower, right? But WHO CARES! It takes 20 horsepower off the top end, not the bottom end... and does not effect the electrics at all. So my max. output is maybe 135HP vs. the 155HP possible at sea level.

Now, how often is everyone at max. power output? Rare to never.
I never miss the loss of a few HP at the top end, but I enjoy increased fuel economy every day, year-round.
:shade:-John

P.S. You actually want WARM air intake, not cold. Only gasoline vapors burn. Liquid gasoline will not burn, and will go right out the exhaust.
At cold temperatures, the gasoline will atomize ( go into a fine liquid mist ) but not vaporize ( go into an invisible gas that burns ). You will waste more gas, and cause more pollution with cold air vs. warm.

Re: Temperature and Fuel Economy
 

Of course Temperature plays some important role for car fuel economy. It effect all parts of our car like bearings, joints, transmission, power assisted brakes.