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Old 11-15-2018, 09:45 PM   #6 (permalink)
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ThermionicScott's Avatar
Join Date: Dec 2016
Location: CID
Posts: 362

Winter Sacrifice - '96 Subaru Outback
90 day: 25.34 mpg (US)
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Originally Posted by bradlington View Post
All noted - I am very interested in the science behind the mechanics .

To ThermionicScott- can you share what you have done for fuel economy on your Subaru .
Hey Bradley.

Nearly all of my mods and techniques are straight out of the "65+ efficiency mods" and "100+ hypermiling tips" at the top of the site:

1) ScanGauge to give instantaneous feedback on MPG as well as coolant temp and trip MPG. Watching MPG plummet when idling or accelerating hard are powerful influences on driving technique.

2) Tires filled up to around max. This was pretty eye-opening when I first read it: Since Subarus need slightly more air in the front tires (placard is 29/28 for my car), I shoot for 45/43 or thereabouts in the summer, a few psi less in the winter snow and ice when you want tires to be a little more compliant. I can feel a difference in coasting distance if I let the tires get low.

3) Grilles blocked as much as I dare. Here again, the ScanGauge dramatically shows how much better my gas mileage is with a warm engine, so I try to hurry that up as much as possible.

4) Use of block heater in the winter. I didn't even know my Subaru had one when I bought it, but it gets the coolant about 50-60 degrees warmer than ambient when I remember to use it. That helps.

5) Lightening. I had no motivation to keep my car clean before, but now there is no clutter inside and I removed the layer of carpet and foam from my trunk. (Unlike some, I'm going to keep the spare tire and jack, though!) I haven't been able to quantify the improvement from this, but I figure it's good practice if nothing else.

6) Thin oil, filled below "Full" line. My car's manual specifies 5W30 or 10W30, but I use 0W30. My initial reason for this was to make sure it would start on the coldest Iowa days, but anytime the oil flows more easily, less energy is wasted to pump it. There is a thought that oil will come up to operating temperature a little faster if there is less of it in the system, but you wouldn't want to run below the "Low" line on the dipstick, and it's not a good idea if your car leaks or burns oil.

Beyond that, it's all technique. I shut down the engine whenever I won't be driving the car within a couple seconds, I coast in neutral a lot, I try to time traffic lights to avoid stopping, etc. My car is old and wearing out, so just meeting the EPA rating would probably be good, to say nothing of beating it by a little.

Best tank (so far): 32 MPG
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