2015 Subaru Forester: Great gas mileage in warm weather; lousy in cold weather. I live in Minnesota. What to do? Put in hotter thermostat? Dealer has no advice.
Completely normal, that’s why the dealer has no advice.
How bad is “lousy?” I have a 2016 Forester (Auto CVT). The display of the average is about 30 MPG all year except winter when it drops to about 29 MPG. When I verify the display at the pump (miles driven by gallons consumed) I find it is about 1 MPG optimistic. What is you mileage? Do you adjust your air pressure (add air to make up for the PV=nRT drop?) Here are common reasons why a car (any type of car) has worse fuel efficiency in winter.
And, the practice of “warming up” a car by letting it idle cuts into MPG. Start the car when you are ready to go, let it run for 5-10 seconds, then go, gently for the first couple blocks.
And, be sure to check the tire pressure, which decreases ~1 psi for every 10 degree drop in temperature.
The folks who blindly rely on their car’s Tire Pressure Monitoring System-- rather than actually doing a manual check of tire pressure–are almost always driving around with “soft” tires after temperatures drop.
I have the same problem with my 2014 Legacy and it is NOT due to warm up or tire pressure. I never “warm up”, in fact I don’t even wait the 5 or 10 seconds unless it happens to take me that long to put on the seat belt. I am a tiny bit, just a tiny bit I tell you OCD about tire pressure. Don’t get me started.
The problem, at least in my case is the CVT transmission. Below 45 degrees F, it holds the gear ratio lower, causing the engine RPM’s to be 2-400 rpm higher. It’s like a cut off, 46 and it is normal, 45 and the engine revs more, even after it is fully warmed up and it cuts the gas mileage by about 10%, from 30 mpg to around 27 mpg.
When I get on the highway, I shift to manual and upshift to 6th range. It’s always in 5th when I go to manual. For some reason, after I do this for a couple of minutes, it stops hanging in the lower ratios even back in auto and back in town. BTW, your CVT is programmed differently than mine as in 2015 they went to simulated gear changes, but it might still have delayed shift points in cold weather.
The engine has to heat the coolant and incoming air up to the same temperature irrespective of the ambient temperature. The colder it is, the more temperature rise required, which uses more energy. And the only source for energy is the gasoline. So in winter some of the energy in your gas tank is being diverted to producing heat, and not moving the car, resulting in lower mpg. The more often you drive short trips, the more you’ll be in warm up mode, and the higher % of the time you’ll be paying to heat the incoming air and coolant. The other effect is the longer the coolant temperature is below the fully warmed up state, the longer the computer has to inject extra gas to meet the richer mixture needed. Suggest to take a long trip and measure the mpg then. I expect the mpg decline won’t be as much as you are noticing during your driving schedule which I presume includes many short trips.
If after all that you still have unexplained mpg drop, make sure the coolant is actually reaching operating temperature, and as quickly as it should be. And that all of the wheels are spinning freely; i.e. one of the brakes is not partially applied. try feeling the temperature of the wheels after a trip that didn’t include much hard braking. If one of the wheels is much hotter than the others, that’s a clue.
@George_San_Jose1, I agree with your theory and every car I’ve had has dropped some MPG in winter, but not to the extent that my Subaru does.
The 2015 Subaru Forester is rated at 23 MPG, I would expect 18 to 20 MPG during cold weather, 27-29 MPG seems unrealistic for the average driver.
24 city/32 highway. 27 combined
24 MPG for the 2.5 L engine but 23 MPG for the 2.0 L Turbo. Customers rarely complain about highway fuel economy, that is easy to achieve, it is the daily city mileage that is lower than expected.