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Old 01-09-2018, 01:05 PM   #1
FrostyRex
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Default Cold start fuel consumption

Long story short I got gas last night, drove one mile home after clearing the trip odometer, and got 20.1 mpg. This morning during a cold start I went from 20.1 down to 9.6 mpg before it warmed up.

I've always felt that the mpg was a little low in my WRX, but is that normal for a cold start to use that much gas?


2014 WRX, Invidia Catted DP, R400 Catback, Stage 2 OTS map
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Old 01-09-2018, 01:09 PM   #2
whispering_eye
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I assume you probably filled up, reset your odometer and maybe put on 25mi since fill up. With that little miles a cold start will consume a lot of gas hence the number you saw. You probably let it warm up without driving as well I assume which means no mi's driven and lots of gas burned. Wouldn't think anything of it; it's a cold start and that turbo needs to warm up.
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Old 01-09-2018, 01:16 PM   #3
Charlie-III
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To figure MPG, best bet is most of a tank based on "your normal driving". Checking after a fill and doing a track day WILL kill MPG.
Doing a long steady state highway run at "reasonable" speeds will help MPG.

Goal is to check tank to tank for normal driving. Ignore the dash gauge (if you have one.....), divide miles driven by gallons put in, smooth the avarage over time.

A consistent drop could be worn plugs, low tire pressure, dragging brake. Look to long term, not a few miles.
Some parts of the country, we get different fuel between summer and winter, that makes a difference as well.

Take this from someone that has logged (on paper) many things in over 40 years....
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Old 01-09-2018, 01:52 PM   #4
rtv900
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yes, normal.

That's why engines want to warm up as quickly as possible.
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Old 01-09-2018, 02:48 PM   #5
viper_crazy
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I'm sure many will have opinions on this but during colder temps (winter) you car really only needs to be running about 1-3 minutes on cold start before you can start driving. Anything longer and it's just personal preference (I.E.: don't want to drive a cold car). Drive with a light foot until it gets warmer (say, 1/4 way warmed up). Engine will warm up sooner and reduce needless idling wear on your engine, and you will save all that fuel for actually moving the vehicle instead of parked and idling.

Of course, block heaters are a good investment or if you have a heated garage, sell all your crap and park in there.

The computer calculates fuel used vs distance driven. So if you've done a fair bit of accelerating during your fillup to home, you'll always use more fuel accelerating than cruising so the computer reflected that. Less miles driven means less of an average the computer has to calculate.
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Old 01-09-2018, 03:33 PM   #6
rtv900
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Quote:
Originally Posted by viper_crazy View Post
I'm sure many will have opinions on this but during colder temps (winter) you car really only needs to be running about 1-3 minutes on cold start before you can start driving..
I wait 10 seconds tops.
no way I'm sitting in there for several minutes freezing
If I start driving I swear the heat starts working within a minute in this car. By far the fastest warming up car I've ever had (interior heater I mean)
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Old 01-09-2018, 03:41 PM   #7
Vancouver98STi
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Quote:
Originally Posted by viper_crazy View Post

...if you have a heated garage, sell all your crap and park in there.
Or keep the crap and park in there anyway.

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Old 01-09-2018, 04:28 PM   #8
Valarius Starchaser
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Originally Posted by Vancouver98STi View Post
Or keep the crap and park in there anyway.





I just died of laughter
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Old 01-09-2018, 04:33 PM   #9
viper_crazy
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Originally Posted by Valarius Starchaser View Post
I just died of laughter
+1! I nearly spit out my sandwich.
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Old 01-09-2018, 05:59 PM   #10
Max Capacity
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You do realize winter gas is different then summer gas, winter gas gives lower mpg's.

I also don't let my cars warm up in the driveway, start it and drive it. It warm's up faster.
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Old 01-17-2018, 03:32 AM   #11
FrostyRex
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Thanks for all the responses! Just got around to checking this. I do feel that my mpg's are a little low compared to what subaru advertises. I get about 23.5 if I drive 100 miles on the highway at cruising speed with almost no hard acceleration and 17 mpg around town. Supposedly I should be getting 19/25, but I guess I never really do completely stay out of boost when I drive.
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Old 01-17-2018, 07:44 AM   #12
viper_crazy
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What car manufactured advertised is under perfect conditions, which most people never see.

What your getting seems pretty normal.
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