I get ~18 MPG in my Impreza, and even though my fuel mileage sucks I still take steps to improve my fuel mileage. Just because my commute is short and I'm flooring the car down the on-ramp to the highway doesn't mean I don't want to take steps to improve my mileage within the boundaries of how I want to drive my car. For instance, is it better to be in second or third gear when in slow but flowing traffic?
In the same sense, I'd like to know how my computer usage is affecting my battery life. Do the extra tabs I have open in chrome matter, or should I bookmark them and close them until I need them? Just because I value one thing over another, doesn't mean the less valued option doesn't come in to play when making a decision.
I know my gas mileage is dominated by flooring it down on ramps, but my mileage is still affected by a lot of other factors. I track basically everything I do with my car, along with mileage, and small things make a surprising difference. I can detect a change in my fuel consumption based on what tires I have on my car, how old my oil is, whether my roof rack is on my car, and whether I have my bike mount on my rack.
Those effects are noticeable on my normal commute, where I travel 8 miles and spend most of the time going less than 30 mph, where aerodynamics doesn't matter that much. When I take a road trip (and thus don't have to perform any suicide merges), the difference any of these things makes is quite substantial. My summer tires are each about an inch wider than the tires I have mounted on my old rims, and switching to the narrower tires makes more of a difference in mileage than taking off the roof rack. With the narrow tires and no roof rack, I can get about 36 miles per gallon at 55 mph, and with my winter tires and my roof rack on my car I can't even approach 30 MPG.
For a tech-related example: I prefer to use my phone with the backlight turned all the way up, even though it uses an additional 15% of every full charge, but I uninstalled the Facebook app because it used 3% of every battery just running in the background.
I'm just trying to be efficient in my own way, I'm not competing on efficiency.
Turbo or non-turbo Impreza? I had a WRX (turbo) for nearly 10 years and I don't think I ever got below 25. I'm surprised at 18 - I would consider that really low. I don't know your scenario, but I would guess that you could do much better than that with just a few changes. I've never had to floor it on an on-ramp, but I haven't driven everywhere in the US.
I assume you have a manual transmission? Which engine do you have?
A huge part of why my mileage is terrible is because I basically have the worst possible commute for fuel mileage. live in Chicago, which supposedly has the worst traffic congestion in the country. My commute is only about 8-10 miles, but there is a lot of variation in speed. I can go from stopped to 65-75 miles an hour back down to stopped several times on my commute. The commute takes about 30 minutes, and I spend a lot of time idling.
Obviously that is a ridiculously low mileage for a car, even given the conditions. My fuel mileage never dips below 18 mpg for an entire tank, but it rarely goes above 20 mpg unless I leave the city. Looking at similar vehicles on Fuelly, I don't think it's that far out of the norm.
My Impreza is a 2010 OBS, with the 2.5L NA EJ25, and a 4EAT. I think what really kills my mileage is the 4-speed automatic. From what I've read, it's absolutely brutal on fuel efficiency compared to the 5 speed manual. The NA uses a lot more fuel than the turbo when just puttering along as a result of its higher compression (10.0:1 vs. 8.2:1) It's not necessarily a negative - my car is faster off the line than the turbo, especially after sitting in traffic on a hot day.
I know the WRX has a DOHC engine, whereas the 2.5i is SOHC. That probably makes some difference in efficiency, though I don't know how much.
On top of that, I almost always have my roof rack on if I'm driving in the city, and I usually have a bike rack mounted as well. Plus, I have the hatchback, which I've heard also impacts mileage, though I have no idea if that's true.
I've also replaced the somewhat narrow stock-all seasons with wider and softer tires summer tires. I run high sidewall winter tires on steel rims in the winter, which weigh a lot more than the stock alloys/all seasons.
Regardless, the Impreza really sucks at city mileage compared to other cars because of the added weight and drivetrain losses of the AWD. (As you probably know) It's really no surprise the 2.5i and 4EAT have been replaced by a much smaller engine coupled to a CVT.
Yes, I had a manual transmission. I assumed your comments regarding "second or third gear" implied you had a manual transmission. Automatics have come a long way in the past few years in terms of fuel mileage, but "slushboxes" like yours are probably the worst. I didn't know the Subaru automatics were that bad. I do know the new 2.0 with a CVT yields good results. It sounds like your driving pattern forces you to be in the worst fuel mileage ever (lots of time idling plus several bursts up to 75? ouch!). I assume you've explored other routes for your commute. Even something where you are driving slowly but not stopped/highway speeds should give a marked improvement.
The hatchback probably doesn't impact your fuel mileage much. I don't think the difference between DOHC and SOHC is going to have any measurable impact on fuel mileage either. Nor would I assume that a compression ratio change does that much. Your final drive ratio is probably the most significant impact. Additionally how much time you spend in "lockup" mode (where the fluid clutch is essentially disengaged and the engine crankshaft is directly connected to the driveline) is a major contributor. The roof rack absolutely impacts fuel mileage as Consumer Reports demonstrated: http://www.consumerreports.org/cro/news/2013/07/tests-show-b...
I use the manumatic function a lot in my 4EAT, because it always seems like it's in the wrong gear otherwise. I test drove a 5 speed and I hated it, cause the gearing seemed horrible for the speed limits which are really common around me.
Anyways, I take the highway to work, and I take a short stint on a highway and then surface streets on my way home. On my way home I run in to something like 40 stop signs. Pretty much every intersection has a four way stop for a few miles of my commute.
I can actually quantify how much the roof rack affects mileage, because I track whether I have it on my car or not in addition to my mileage.
In the same sense, I'd like to know how my computer usage is affecting my battery life. Do the extra tabs I have open in chrome matter, or should I bookmark them and close them until I need them? Just because I value one thing over another, doesn't mean the less valued option doesn't come in to play when making a decision.