Gas mileage

I have a 2009 Chevy Impala. It has 28,000 miles and since November my gas mileage averages between 20-24. I took the car to the dealership and they say nothing is wrong. This car was titled in Hawaii. I live in Wisconsin. Could the colder weather have something to do with the mileage or what else could it be???

You need to tell us what engine you have and the type of driving you do. Here’s the city/highway/average mileage for the gasoline (not E85) engines:

3.5L 6-cyl: 18/29/22
5.3L 8-cyl: 16/24/19

If you have the V8, you are getting great gas mileage. If you have the 6-cyl, your mileage is average for half city/half highway driving. Also, the formulation is changed in the winter for smog abatement purposes. That drops mileage slightly (~10%), too. I don’t think there is a problem, but tell us what engine it is and whether is can use E85 or not. If you are using E85, your mileage will be awful, BTW.

3.5L 6-cyl. Most of it is highway. I bought the car last feb. and I averaged 26 city/highway, it was 28 during the summer as soon as the cold weather hit this year it nosedived. I have always checked my gas mileage every time I fill up. Of all the vehicles I have owned I have never had gas mileage get that bad. I have an 03 silverado V8 and I get 16 in the summer and only drop to 14.5 in the winter. 14 if i use 4 wheel drive on occasion.

I do not use the E85

Please excuse me if I have mis-read anything.

First congratulations on keeping track of your mileage and properly computing it.

I will suggest that part of the problem is winter fuel. In many places Winter fuel is used to decrease the pollution and it may or may not be noted on the pump.

Cold weather means less efficiency so that will also take a little bite.  We also tend to take shorter drives when it is cold and may let our engine warm up before we drive, all contributing to lower mileage. 

 Having said that, when was the last time you:
  • Replaced the air filter
  • Replaced your spark plugs
  • Did an oil change

Are any of those now due?

That drop in mileage between winter and summer is reasonable. The gas blend is different in winter and yields slightly lower MPG. The cold also means that the car starts from colder and takes longer to warm up all the while running richer (b/c its supposed to when it cold).

The other thing that nosedives when the weather turns cold is the air pressure in your tires. But you didn’t say whether you watch that or not.

oil change is done every 3,000. It was just done. It only has 28,000 miles. The dealership said they checked everything. If I had a bad spark plug or wire the car would miss wouldn’t it?

Plugs & plug wires, in addition to filters do not have only two states (working vs. not working). They degrade slowly over time and all the while the performance drops. By the time you notice a misfire they are very far past their prime. That said, I doubt that your plugs/wires are an issue at this age/mileage.

Fuel & air filters maybe.

But as noted, what you’re seeing may just be normal.

Thanks for all the imput. Just was concerned that a drop of 6-8 miles from summer to winter was a bit much.

If you’re not back to summer mileage when the weather warms then you can chase it. The basic things to check are:

  • tire pressure
  • air filter
  • fuel filter & fuel pressure
  • plugs & wires
  • brakes - to make sure they’re not dragging
  • cooling system, especially thermostat & coolant temp sensor.
  • alignment
  • accumulation of weight (my trunk tends to just keep collecting things over time that I toss in and forget about)
  • O2 sensors can be scoped for proper operation
  • …and I’m sure a few other things.

Cold weather and the fuel additives for the winter cause the drop in MPG. Normal don’t worry about it.

20-24 MPG is exactly what the car should be getting. The dealership is correct, there’s likely nothing wrong with your car. And yes cold weather will cause a dip in fuel mileage.

There is nothing wrong with the mileage you are getting in the winter, nor with your Impala.


I do not use the E85
What does that have to do with anything? The blend change from summer to winter is not related to E10 or E85, and it is not something you can choose.

A few more things to check. Cold weather can cause tire pressure to be low, check the tires and pump up to about 32 lbs pressure.

Perhaps a caliper is frozen or sticking. Get the car up on a lift and check for a brake hanging up by spinning the wheels. There should be little to no binding and the wheels should spin freely. While the car is on the rack check for any wheel bearing play.

If the motor is OK, basically you are checking for any rolling resistance which can impact mpg negatively.

Go to Auto Zone, or any parts store and get a new air filter and install it.

I mentioned E85 in the first response since ixonia did not tell us what engine is in the Impala at first.

Spark plugs and spark plug wires are probably not due until around 100,000 miles. Your maintenance book in the glove box will tell you when it is normally called for. This is an expensive job these days because the rear plugs are not easily accessible. If all else fails, check into plugs and wires, but don’t go there first.

Fuel is changed for summer conditions not winter. I have been in the air pollution monitoring buisness. I actually check the performance of changes in fuel blends by regional air pollution monitoring. The summer fuel contains more oxygenate to reduce air pollution caused by photo chemical smog. Why? Because we get more sun in summer than winter. More sun= more smog. DUH. Air temps cause winter fuel consumption. Cold engines need more time to get to the combustion temp than warm ones. Bad temp sensors are really common. Check the temp sensors its easy with a OHM meter. A bad one in a cold climate can cost you %10 fuel milage if you take short trips( less than 20 mi).