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Discussion Starter #1
This will probably be my first post so please be kind. Lol. So my gas mileage has gone bad. I'll start from the beginning. Sorry if it becomes a long post. I bought my 2006 forester xt last May from the subaru dealer in Scarborough (Toronto Canada) with 59xxxkm. I was told it was traded in off lease. Sunoco ultra 94 has been put in it all the time. I have approx 70xxx on the motor now. It's been oil changed three times since buying. Reason being the first time I put mobil1 in and found out that it's not too good for subbies. Royal purple 5w30 has been used since. Now for the problem.
I've been monitoring the gas mileage since I got it writing down the mileage after each fill up. I"ve probably missed writing it down once,twice at the most. Here are the results I've got. I calculate both litres per 100km and also mileage bc that is what I am used to seeing because of reading the US car magazines.
27.26. 21.71 26.27 19.58 24.65 18.43 20.99 20.57 21.57 19.11 21.88 22.46 19.26 20.75 20.44 18.52 19.28 19.01 18.96 21.36 22.88 15.86 21.30 17.17 13.75mpg being the last one I did a couple days ago. I've been told that my mileage was a little high for an xt. I do city mixed with highway. Sometimes they were all highway. Obviously your mileage drops in the winter bc of heater use and gas additives.. Dropping 7-10 miles per gallon is normal? I have no mods on my vehicle except a samco ypipe when I bought a helix tmic but decided to keep it stock and left the samco hose in. Any suggestions on problems? Or am I just finding a problem that is not there? was thinking because it is my first winter to let it go and see if it goes back to normal in the spring. Also I'm told the winter gas has more additives in it to cause mileage to drop. I don't know if it's just me or bc i read that on another thread that the poster smelled more unburned gas in the tailpipe. In terms of the way the fxt has been running I think it runs a bit rougher since the cold weather has come. But the power is still there. What do you think? Am I crazy? LOL.

thanks for reading my long post...
 

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06 Forester
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There should not be that much dropp for a stock XT.
Back when i had my WRX i was averaging about 18mpg in winter and the car was heavily modified plus my right foot was always ready to have fun.
21mpg is right about what you should be getting. If you drive hard and stay on boost for long then you may see drop down a little but certainly it shouldn't dipp below 18mpg.
Highway trips should yield you around 23-26mpg.

but this being said here is the quick list of things that affect winter mpg:
- winter gas blend (may not affect you in Canada)
- lower pressure in tires due to cold
- use of winter tires
- oil in engine being cold and to thick (try 0w30 or 0w20 for those particular cold months)
- oil in transmission and diffs getting thick due to cold temperatures

All these things can contribute to higher rolling ressistance therefore decreasing your gas mileage.
 

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Discussion Starter #3
Thanks for the quick reply. Actually my tire pressures were out of wack showing 20psi onall four. So that couldve contributed also. I have been on boost more then I should lately. Usually when boosting I'm revving to around 5000 rpm. When I was milking I wouldn't pass 3000rpm. Also winter warm up I idle a lot. The easiest I can do is after next fill I will drive like a granny n see what that does.
 

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1999 Forester S w/AT
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Thanks for the quick reply. Actually my tire pressures were out of wack showing 20psi onall four. So that couldve contributed also. I have been on boost more then I should lately. Usually when boosting I'm revving to around 5000 rpm. When I was milking I wouldn't pass 3000rpm. Also winter warm up I idle a lot. The easiest I can do is after next fill I will drive like a granny n see what that does.

Low tire pressure will definately have a bit of an impact. However, if you idle to let your car warm up, you are really wasting fuel. To warm up your car well, start it, scrape off all of your windows of any frost, get in, and drive. Keeping rpms below 3,500 is a good ballpark and stay out of boost until it warms up.
 

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Discussion Starter #5
Yea that's wat I do. Actually I wait a minute on regular days n a minute and a half on colder days n don't rev past 3000 with no more than half throttle till temp up. I'll drive off boost next gas tank n see what that does.
 

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2008 2008 2.5i-2018 XT
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I plan on going back to NGK's. I am suspicious that the Autolite's that I put on 13,000 miles ago are delivering the gas mileage of the original plugs. I will do it as soon as the next decently warm day gets here.
 

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2015 Forester X 6MT 6-Gear Manual
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I plan on going back to NGK's. I am suspicious that the Autolite's that I put on 13,000 miles ago are delivering the gas mileage of the original plugs. I will do it as soon as the next decently warm day gets here.
ADC - If you dont have a noticeable misfire-count increase or loss of torque I dont think the plugs are a problem. My Yaris is down 6MPG this winter - and never was a problem last winter. My wifes subaru was down to 25 from 29mpg then she said she had pinging and she is running premium and now she gets 28. I think the winter fuel this year is below rated octane and loaded with ethanol. I havent ordered a ethanol test kit yet to confirm.

see link:

Order page - Ethanol Alcohol Fuel Test Kit.
 

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...if you idle to let your car warm up, you are really wasting fuel...
lol. :crazy: Why do you believe that letting one's car warm up during idle is wasting fuel? I know the following to be true for every Electronic Fuel Injected car:

1. The engine runs rich (i.e. more fuel) when it's cold (because fuel does not atomize as well in a cold environment)
2. Engine runs more stoich (safely leaner) after it's warmed to operating temperature.
3. Engine ALWAYS burns more fuel when it's under load and LESS fuel when it's not in load (i.e. neutral / park)

When you drive a EFI car while the engine is still cold, you're now running pig rich air/fuel ratio's while the engine is under load...so you waste even more fuel washing your cylinder walls with fuel. It's always healthier for the engine (and its seals) to warm up before driving it...unless you like wasting fuel.
 

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2000 Forester S
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lol. :crazy: Why do you believe that letting one's car warm up during idle is wasting fuel? I know the following to be true for every Electronic Fuel Injected car:

1. The engine runs rich (i.e. more fuel) when it's cold (because fuel does not atomize as well in a cold environment)
2. Engine runs more stoich (safely leaner) after it's warmed to operating temperature.
3. Engine ALWAYS burns more fuel when it's under load and LESS fuel when it's not in load (i.e. neutral / park)

When you drive a EFI car while the engine is still cold, you're now running pig rich air/fuel ratio's while the engine is under load...so you waste even more fuel washing your cylinder walls with fuel. It's always healthier for the engine (and its seals) to warm up before driving it...unless you like wasting fuel.
^^ Very well stated. Couldn't be more true
 

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2015 Forester X 6MT 6-Gear Manual
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A car gets 0 MPG when its running and sitting. In approx 2 mins a heated o2 sensor should be operational, ECM at closed loop and running the car at near stoic (+ fuel adds for low coolant temp). If you drive ( or just creep) away slowly with near closed throttle and low RPM you should acheive better ave MPG by warming your vehicle less than 2 min @ cold start idle.
 

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2015 Highlander AWD XLE 6AT
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Some suggestions from CAA:

Use a block heater. It can improve fuel consumption by up to 15%, and more, on distances not exceeding 20 kilometres.

In cold weather, you need only let the engine idle for 30 seconds, then drive while avoiding heavy acceleration.
More on the block heater.

Download a related pdf.

HTH,
Jim / crewzer
 

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2011 Forester Automatic
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Low low gas mileage on New Forester

My new forester has a computer showing gas mileage. It has dropped from about 26 mpg to 17.7 mpg in one tank of gas (the first added since purchase). All city driving but each day drops 1 mpg. As I'm moving along it keeps going down. Yesterday dropped to 18 mpg and today drove about 30 minutes and it dropped from 18.0 to 17.7 mpg. Any idea why mileage drops so much?
 
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