Cold weather and tyre pressure.
I am in New Jersey. As near as I can tell, we’re running about 10% Ethanol these days.
Have you been pushing the speed? When I commuted 100 miles R/T, the difference between 65 and 70+MPH accounted for 25 or more mile difference on a tank.
“I have a wrench in my hand and I’m about to do some major damage... “
What could possibly go wrong? Go for it.
Mine always drops off when the summer blends come in, plus the cold temps mean the gasoline is more concentrated.
Gas has some amazing thermal expansion properties. Ethanol percentage is a big factor too.
Alcohol in the fuel.
Ethanol in fuel = less energy available per gallon. *IF* your fuel now has entered the ‘oxegenated’ phase of the year, then yeah, your mileage will drop.
The rest falls into driving practices and mechanical condition.
I bet it’s the fuel blend - my car has the same problem. With no ethanol, the car would routinely get about 330 miles per tank, but now it gets about 260 ... double-plus ungood!
Don’t rule out the winter fuel blend. You might be back to normal once they go back to warm weather blends.
1. How old is your car? If it's an older model (but still fuel injected), it's time to see if the fuel injectors have become dirty. Cleaning the fuel injectors--especially if the vehicle has over 60,000 miles on it--does wonders for power and fuel economy.
2. See if the fuel filter needs to be replaced, especially if your car is more than three years old.
Same thing has happened to mine, and I’m also in New Jersey.
I suspect more alcohol in the fuel.
I drove the '08 Prius locally, getting 54.4 miles to the gallon. No complaints there. By 2013, I noticed the mpg in the '08 dropped to 40.8. I chalked it up to the cars age, wear, and change of routine. I no longer own that '08 vehicle as the batteries were needing replacement soon.
Perhaps there was more to consider with the mpg decline, given your post. I'm curious to see how the comments on this post develop.
I have no idea. 5% is not worth getting your panties in a wad.
I'd say the cold weather. But we know that Ethanol kills gas mileage. Hopefully that will disappear one of these days. Drill Baby, Drill.
Summer blends are here! This is deliberate. If you want to “fix” it, try buying an ethanol stabilizer or use Sta-bil in your car.
Otherwise, get your tires balanced and rotated, and make sure your shocks, struts, and brakes are in good working order. Your suspension system has a greater impact on your gas mileage than you think.
I drive a Ram with a 5.7L hemi. I see differences in mileage with different brands of gas. Running Sunoco is like flushing a commode. My mile drops a lot. I think ethanol is the problem.
Did your state recently mandate ethanol usage?
If so, you’re lucky it’s only dropped 5%.
Mine is actually a bit (+/- 1-2 mpg) better in the last two months. It was hovering around 26.8 mpg and now reads a solid 28 mpg