Hopefully, it’s a simple fix (hey, it could, in fact, even just be low tire pressure!)
Is it possible you had been buying gas previously that had little or no ethanol in it? 10% ethanol is common at most gas stations, and it can reduce mileage by about 5%. Marathon and Sunoco are two brands that tend to sell non-ethanol gas, but it’s still very store-by-store. That’s not enough to explain the whole drop, but maybe part of it.
Also there’s a summer versus winter component. Summer gas is less volatile (helps reduce ozone pollution) and actually has a slightly higher energy density, but hot intake air reduces volumetric efficiency of the engine. In winter there’s better volumetric efficiency but more wind resistance at highway speeds and longer warmup times. Granted those should even out over a year.
Another possibility could be something like a failing A/C compressor causing increased drag that would sap power from the engine. I’m also suspicious of the new tires as well, especially if the old ones were hard and balding. Again, that may not be the whole story, but it could be part of it.
Gas is always 10% ethanol, so that’s not it. Checked my tire pressures, one was about 2 lbs low, so I don’t think that’s enough to drop the mileage by almost 15%. Is the fuel filter the next thing to try, or should I get the spark plugs changed?
StG
If you’ve never changed the fuel filter, try that next IMO.
This is my bet. The new tires are taller than the previous ones. The car determines the speed by literally counting the tire rotations. With a taller tire, the tire will make fewer revolutions to go a mile.
Taller tires make the computer think the car is moving slower than it actually is. Or, to put it another way, the car is going faster than you think it is. Your car gets worse gas mileage the faster it is driven.
So, when you odometer tells you that you have traveled 100 miles, you have actually traveled farther. You are using the shorter distance (now) to calculate your MPG.
The 2012 Rav 4 came with three wheel sizes, 16 inch for the base 4 cyl, models, 17 inch for the base 6 cyl and Limited models, and 18 inch for the sport models. I don’t know what model you have, but assuming 17 inch wheels, the standard tire would be 225/65R17, which is 28.5 inches tall. If the tire shop put on 235/65/R17 tires on there, they would fit, but have a bit taller sidewall and end up being 29 inches tall, or 1.8% larger. They would also have a wider “patch”, which would give you better traction, but would also hurt your mileage.
Take a look at the tire size listed on the sidewall of the tire. Also, the tire heights are calculated. Different manufacturers may have slightly different heights for the same size tire.
Fun thread. Placeholder.
This was going to be my suggestion. I keep a log in my car every time I fill up. I was getting about 21mpg when I was used to getting 24mpg or so. I changed the fuel filter and it went back to 24mpg right away.