As the weather warms up, I'm noticing that my vehicle's fuel consumption appears to have improved, despite little change in the (horrendous) city traffic that I've been dealing with on my daily commute. I chalk this up to three potential (and possibly simultaneous) factors:
1. fuel composition - perhaps because of the warming temperatures where I'm at, the local refinery might be starting their process to convert to summer blend
2. reduced need for directing the vents to the windshield - meaning, less A/C being used (I still find it weird that Subaru doesn't turn on the A/C light even though the function is being used, I wish they wouldn't pander to stupid people)
3. car's break-in / wear-in reducing overall friction - I'm almost at 11,000 km (6,800ish Miles, for those of you not on the metric system). The car has already had one oil change performed at around 6,900 km (just under 4,300 miles).
There's also potentially a fourth variable in play, which is air temperature. Cold air is more dense, requiring more energy to push the car through the same volume of air compared to warmer air, all other things being equal. However, I'm not an aerodynamics specialist.
My total overall average fuel consumption (estimated city/hwy ratio is about 90:10, with 70% of that 90 in the legendary craptastic Vancouver stop-and-go, red-lights-and-stop-signs-every-****ing-100-metres traffic) is currently at around 9.6 l/100 km (24.5 MPG), and is improving with each fuel-up. Windshield air vent use over the 10,000+ km is close to 80 on/20 off.
My most recent tank (at 10,525 km, 6,540 miles, with ratio closer to 85:15) was just a tad over 9.2 l/100 km (25.56 MPG). About 50 on/50 off windshield vent use.
My most recent road trip (at 9,500 km, 5,900 miles, for about 450 km, or 280 miles) consumed about 7.4 l/100 km (31.8 MPG), and that was with a ratio of about 20 city:80 hwy, with city traffic being much more reasonable than the p.o.s. Vancouver traffic. "Highway" speeds here in BC are generally between 60-110 km/hr (37-68 MPH), with most "highway" speed limits (ie. 60-65%) pegged at between 80-90 km/hr (50-56 MPH). About 60 on/40 off windshield vent use during my roadtrip.
My current tank might break 9 l/100 km (26 MPG), with about 90 city:10 hwy, and 30 on/70 off windshield vent use. Based on the current tank's usage figures, my car might even make a run for breaking 8.5 l/100 km (27.67 MPG).
All figures are hand-calculated from fuel filled vs. km between fuel-ups. I haven't been purposely "hyper-km"ing it (and wouldn't be able to anyways, given the ****ty traffic in Vancouver). Take those figures as you will.
EDIT: For the record, my vehicle has 16" wheels.