Temperature Effects
 

I was number crunching on my daily log data and thought folks might find this interesting. I plotted 80 days (160 commutes) worth of mileage and ambient temperature data:
http://ecomodder.com/forum/member-di...e3564-temp.png

Mileage goes to the left axis, temperature to the right.

Like everyone else, I can't wait for it to warm back up!

Try cross plotting temperature against gas mileage. Temperature on the horizontal axis and gas mileage on the vertical axis.

Okay, here you go:
http://ecomodder.com/forum/member-di...3565-temp2.png

40 deg F change results in about a 20% change in mileage. So mileage changes 1% for every 2 deg change. That's pretty significant.

Awesome !

Nice this very good to see.

Nicely done. What were the dates of the 80-day period, and what is the date of the first and last frost for your locale? Any other relevant climate data by which to make comparisons? (or, do dawn/dusk considerations play a part?)

(For us the potential frost period is Nov 23 - Mar 9; with some as years [as this one] no frost at all; January thru first week of February constitute winter"; maybe only 10-days). A/C use is the bugabear for FE.

You "commuters" can certainly have good data to work with in re set conditions of place and time over the year.

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Now, *that's* the kind of number-crunching I like to 'see' -- show me the graphics (ha,ha)!

You've just documented & published the "Diesel Dave's TEMP Rule-of-Thumb":

"... -1% FE change per each -2ºF temp change...and...+1% FE change per each +2ºF temp change."

Dave,
how long is the comute?
Does the vehicle start uotside (so the temp has settled in overnite)
or is it in the garage?

It's from Oct-10 unil Feb-15. It's 80 commuting days--not 80 days. Dates of potential first/last frost are before and after this time. I've had a couple mornings down below 15 deg F and those have been hard on the mileage. The "3-day average Temp" is the average of 3 mornings and 3 evenings, so mornings and evenings are grouped together. Dawn/dusk shouldn't play much of a role because pretty much all of it during that time period would have been when I driving it's still dark enough to have the lights on. Only now, in mid-Feb, is it getting light enough that I can have my lights off much.

I just realized that if you do it in Celsius it would be neater--basically 1 deg = 1% change.

My commute is 24 miles each way. The truck is outside, but I use my coolant and oil pan heaters at home (in the morning). In the evenings it's a true cold start. That's one thing that's not captured very much in the average temperature metric--cold evenings or worse for me that cold mornings, because the heaters help in the morning. That said, it's usually is warmer in the evening, because I'm usually leaving right before sunrise in the morning--which is the coldest point of the whole day.

Also, I should add that I try to avoid using the heater/defroster until I get to full operating temps (usually takes ~12 miles). The exception to that is when I need the defroster/defogger to see clearly. If it's just a little fog, I've learned that cracking the window about an inch with take care of it, but if that doesn't work I use the defogger/defroster.

I have a garage, but the truck is literally about 4 inches shorter than the garage. Plus, my wife's car goes in the garage (of course), and putting it beside hers would make it really tight side-to-side as well. I figured it's just not worth the effort (and risk of damaging the garage, my truck, or her car). Plus, as it is, I can back up the driveway and park at the garage door so I can coast out in the morning. Plus, I'd waste fuel carefully jockeying it into place in the garage.

5 years of commuting data.
Averaged all mpg results at each temperature point.
10 mile commute.
Parked outside, so fully cold-soaked.
Heat off until warmed up (takes most of the trip, so pretty much always off)
No AC in summer.

http://mcguckin.us/files/car/mpg_temp_2011_12.png
That slight flattening at 80+F is because of AM/PM temperature differences. Max morning temp is low 80's so anything above that is driving home, 100 ft elevation gain over 10 miles.

Dave & Pale,
GREAt CHARTS!

How much do you blame on the winter gas formula???

This whole thread is great.


Makes me hope for good things from my Prius that I've never driven in warmer than 45ish degree weather

What about Kelvin?

Man, this is sad, though... no wonder my mileage has decreased (only ~ 20* drop... F, I guess I must now add).

Winter Diesel Fuel

I've seen from 4% to 12% as an estimate (when temps are factored).

Definitely one of my favorite infographics on this site. (Forgot, what part of the state you are in?)

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Pure #1 diesel has about 4% less energy content than pure #2 diesel. Keep in mind, that most areas don't go to a full #1 blend either. Granted, other properties (like cetane rating, etc.) change as well, but especially on common rail diesels like mine, energy content is the main property that matters. Personally, I think a lot of people blame the fuel when it's actually the temperature.

Northeast corner. Pretty far from you. "Everything's bigger in texas", including the distances. :rolleyes:

Oh, and we don't have a different blend of winter gas, so it's all because of temperature.

Yeah, Corpus Christi to Texarkana via Dallas is almost 600-miles. But you're close to Pittsburg and some nasty [great] hot links. Are you old enough to remember Big Al (at Lone Star Steel)?

And you're outside of an EPA Attainment area, so no "summer gas" either. Prior to reading this site I'd have thought that, say, past 90F that mpg would taper off, maybe even decline.

This is a very funny coincidence, since I was doing my own graph two days ago and searched this site if anyone would have published their data, but did not find anything. But a day later this topic appears...

I have been collecting my commuting data over a year and now I wanted to see if my new winter tyres will make any difference.
My trip to work is total 13,7km and I take 3 readings during each trip.
-First after 3,6km of town roads
-Second after a 6,5km highway period @ 80-100km/h
-The last after arriving to my work (3,6km @80 km/h road + town roads)

Also I make notes about the temp, wind, snow, traffic, speed, preheating etc.
I think I can make a thousand graphs with all these variables:p

This graph I made is from the highway part only.
I was very surprised to see how much the temperature affects to the MPG

http://ecomodder.com/forum/member-su...temperatue.jpg

Although there's yet only 2 datapoints, it was nice to see that my new winter tyres (Nokian hakkapeliitta 7) are on the better side than the old retreaded "wintercontact allweather" tyres.
I was afraid to inflate the old tyres over 2,5bar, I thought they would explode. There wasn't even any mention about the max pressure.
The Nokians have now 2,7 bar and the really roll much better.

I'm only 15 miles from Lone Star. :) I've only been here 10 years, so no I don't know Big Al. :( Originally from Aggieland.

We actually are in an EPA Attainment area, but it's from industry not from cars. Those coal plants (Martin Lake, Pirkey, Monticello) do the dirty work and they leave our cars alone.

pale,

Gig'em class of 79

I can't see Pale's plot, but it looks like Super's plot is pretty close to 1% per 1 deg C (just a litle less than that).

Pale, I recall you posting this chart earlier (back in 2009?), and I believe that you gave the linear regression equation for the "black"-line too, correct?

try this if you couldn't see the other.
http://ecomodder.com/forum/attachmen...1&d=1329431649

It's R^2 about .93. The actual data is much uglier than this (R^2 ~0.25), thanks to real-world things like wind and rain and long or short trips. (and my own driving errors) I averaged all the mpg data points at each temperature to get this chart.

Aggies, hmmm. I've noticed since being down here (South and South East Texas) that a an Aggie alum sticker and poor driving habits are too often related. Cut's back in front of me too soon on the highway . . Can't park between lines because only knows how to follow front wheels around (no awareness of vehicle starboard and no clue of vehicle pivot point off rear axle) . . likeliest to cut an intersection corner (out-of-lane during turn; enters oncoming lane during turn), etc. . No, not the worst group, but it's especially consistent when it's a pickup. I wait for a basic driving flaw and it's there every time. Conjecture: Ever since the first Aggie doctorate was awarded in recognition of proof that ice is formed of water success must have gone to the heads of even the C students. Or business students (is there a difference?)

Dave, is there a point along the temp chart where changes are made in how the truck is operated? I got you about frost and daylight, and want to be sure I get it about any other changes (since I wind up trying what you've tried, but have no "elbow rest" of daily commutes to back my considerations). The close relationship of temp and mpg, gas or diesel, is really impressive

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Or like you said 1% per Deg C.
Andd Superturnier's graph,
and PaleMelanesian's graph, which looks a little less steep. Great work!
Although all these seem to be for what I consider short commutes. 10 miles and 14 km. My commute is closer to 20 mi, but my graph would look similar, if...



My question is why? Does anybody vote for higher aero-drag because of denser air? It's a pretty big change, about 15% denser from 40 C to 0 C.
Or do the tires lose pressure, (same density issue)? Or does the engine lose efficiency just from having to start with colder intake air? That's also a surprisingly large effect. Lubricants are stiffer? Some kind of engine warm-up that burns fuel? Is there anything, besides moving, that helps?

-mort

From what I've researched (no references right now, sorry), it's mainly air drag and tire friction. From 100F to freezing, air drag increases 10% and tire rolling resistance doubles. Using the calculator, for the average car that means ~30% lower mpg at 35 mph and ~20% lower at 70 mph. You can add on top of that any extra warmup, lube friction, lower tire pressure if you don't keep up with it, etc.

I made a few small changes (full radiator block & oil pan heaters 10 days in, slight route change after day 20, & lower grille block at day 40). It's always hard to tell exactly what impact those mods had, but my opinion is that the temperature change was the most significant thing. Of course, there's always differences in traffic, how I catch red lights, rain, snow, etc. as well.

I did a little more number crunching and found that the air density changes about 0.5% for every 2 degrees F. The aero drag is directly proportional to the density, so we can account for 1/2 of the change in fuel economy due to increased drag. The rest must be due to the longer warm ups, increased rolling resistance, and other factors.

Yesterday was the warmest day of the year here so far (66 deg F). I was giddy at the thought of being able to drive home! I smashed my evening commute record. My previous record had been 40.6 mpg on a 94 deg day. Yesterday I got 41.9 mpg, with the help of a 10 mph tailwind. Boy, I can't wait for summer!

Data
 

Hi Diesel Dave,
Would you be willing to post the numerical data for this plot, for example in a spreadsheet?
Thank you.

If you send me a PM with your email address, I can pass it along. Also, you might be interested in this, more recent analysis:
http://ecomodder.com/forum/showthrea...log-23740.html