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Old 02-19-2008, 11:02 AM   #1
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temperature vs mpg

Most people here will be aware of the impact of temperature on FE but do you actively compare the temperature to your FE?

since i'm useing tank to tank fillups as my only reference, figuring out if a certain mod is working can be something of a gamble....
i need about a week and a half to run trough a tank and like to use at least two tanks before drawing carefull conclusions, but by that time a lof of weather changes might have occured
sometimes you get the feeling your on your way to a record tank, only to find out at your next fillup things wheren't as good as expected... in the past this got me frustrated but since i plotted a temperature graph of the average monthly temperature in my area next to my fuelgraph a different picture unflods...

temperature has a big impact on my fe and a drop of just a few degrees can cause a serious dent in my FE graph... but it also means i shouldn't beat myself (or a recently installed mod) up over it... not if the drop in fe corolates with previously refistred FE/temp relations

i just mention it, as being aware of the temperature impact can be a good thing while evaluating certain mods over a longer time. especially if you haven't got the time and equiptment to make more reliable assesments.
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Old 02-19-2008, 11:41 AM   #2
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I'd love to but it's hard. with 1 exception (and that was a 96 i drove for 6 months), 1990 is the newest car I've ever owned. so no SG and I can only run per-tank figures. If I could have/build something that would record all that info...instantaneous mpg, ambient temp, water temp, intake charge temp, fuel grade, EGT, throttle, rpm, grade, etc and output it for as long a duration as I wanted and spit it out on the computer I'd need a new pair of pants. even a few of those would be wonderful.
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Old 02-19-2008, 06:21 PM   #3
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This winter weather does really effect your FE. I did some rough estimating the other day and warm weather alone will increase my FE 22% compared to this insanely cold weather.

I think its more mental in my case than physical. I just want to get where Im going ASAP and dont fiddle with gliding or anything. Im currently averaging 45mpg, in the summer i hang around 55-60mpg.
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Old 02-20-2008, 06:50 AM   #4
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Using Scangauge-II on my daily commute for the last year. About 400 data points, averaged for each (ambient) temperature point.
This is full hypermiling, P&G and engine-off coasting and the works, year round. That is, it's an apples-to-apples comparison.
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Old 02-20-2008, 08:05 AM   #5
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I always get worst MPG in the winter.

During january-february we get alot of -20 celcius mornings, and during those I manage to get 15 MPG without even boosting. WIth my previous car (2.2 celica I would get about 100 KM less per tank).

It’s like a triple blow..
1. Cold starts..takes a long while for engine to get to running temperature
2. Air is colder, so it will always use more fuel
3. "Winter-gas", which is said alone to lower MPG by 1 or 2.

Really sucks
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Old 02-20-2008, 09:05 AM   #6
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That is my home brew chart that I use for my VX. The last part of the MPG line where it is shooting up is the first tank of me using the Block heater. It does a fair job of removing the cold start aspect of winter driving. My driving habits and route have stayed the same for the winter driving.

EDIT: I should mention that the "MPG" Y axis intervals are the same for Temperature and MPG.
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Old 02-20-2008, 09:12 AM   #7
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interesting figures PaleMelanesian

if i compare my tank to tank results to the figures from the national weather institute
i get something that's remarkably similar... around 12 - 14 ?C (roughly 55?F) my FE takes a dive.

it's interesting to see that very high temperatures aren't to good either. do you have airco PaleMelanesian?
hot air alone could be an explanatuon of course... warmer air will couse the car to run leaner, but also means loss of power.

i've been thinking lately about installing a cold air intake... since my grillblock i notice when the engine bay starts heating up the car feels a little less responsive.

a big problem in cold weather could be increased friction from cold lubricarion on all bearings and in the engine and transmission ... that will present a rather great "internal rolling resistance" and it all needs to be warmed up by engergy that comes form this friction.

i've wondered for a while if it wold be possible to create a correction factor to apply to ones FE results... thus creating an estimate of how the FE would have been at a certain temperature.
This virtual FE figure might than be used to estimate the effectiveness of certain moddifications, and make it possible to evaluate the effect of cerain temperature related mods with different temperatures.
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Old 02-20-2008, 10:28 AM   #8
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Yeah, I'm not sure about the loss at high temperatures. I used the AC for about 10 minutes total all year. It'll be interesting to see how that holds up this coming summer, with a little more skill under my belt.
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Old 02-20-2008, 08:55 PM   #9
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I'm guessing the cold weather prob is with initial startup; once car is warmed, I'll bet mileage is fine. Here in NC... they use oxygenated fuel in winter. I don't know for a fact, but... seems to me my mileage drops when they start pumping that stuff.
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Old 02-21-2008, 08:48 AM   #10
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I read in a published Ford Research paper that one of Fords fuel labs scientists wrote that for every 10 F increase in temperature gas mileage would increase 1 mpg!

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