Hi. Recently I have seen my highway mileage drop from 24-25mpg to 20.5-21.5mpg. This is actual and not based on the trip computer. I have a 2002 SE automatic with aprox 27k miles. I use the same brand of premium octane gas and have used the same 150 mile section of interstate for my comparisons. I mentioned my concerns to the Nissan dealer at my last oil change. They said everything checks out okay and that the cold weather can account for such a drastic change. Has anyone else experienced this or do I need to check with a different dealer. What might some other causes be? Thanks for any help.

Jeff

 

I would think that colder weather would lower mileage, since you're getting a denser charge of air and the computer is delivering more fuel to compensate.

Additionally, if you live in a state that puts an additive in the gasoline during the winter months, that will lower mileage as well.

 

And you're also driving with the heater on when it's cold, that uses up more gas too...same with A/C in summer...

 

How can turning on the heater reduced gas mileage? Isn't the heat produce by the engine once it's warmed up? Unlike air conditioner system which utilize the pulley (mechanical system) to operate the AC's compressor, the heater unit will only withrawed current from the battery for the blower.

I think the reason for the lower gas mileage is probably due to the oxygenated additives which were added in the gasoline during winter weather to reduce emission in most states that adopted the smog-control policy. As for the cold air, denser air will actually help produce more horsepower which in return will reduce fuel consumption. I believe that is why most people are replacing their stock intake for the cold-air intake system.

 

My December MPG has dropped 2 MPG compared to November. This happens every winter because the cold temperature so it is normal.

 

If you have the aoutomatic climate control, it depends on the setting. The Auto setting always uses the A/C compressor, regardless of temperature setting (so does the defrost setting). I generally use the manual setting and switch to the feet/defrost mode so that the compressor doesn't kick in.

If you use the Auto setting constantly, you will probably see a drop in mileage.

 

It is the gas! Re-check it in the spring time, bet all will be back to normal.

 

Your point is well taken regarding the auto-climate control system. The defrost mode will activate the compressor even in the cold since the AC's air will be dry which will help removed the humility inside the vehicle.

 

Some areas start adding MTBE (Oxygenator) in November and stop in February (most urban areas leave it in all year round). Oxygenators are added in winter because cars tend to burn a bit more rich when the motor is below operating temp. Since the MTBE is carried into combustion directly with the gas, it helps to more competely oxidize all the hydrocarbons, thus reduce emissions, at least according to the folks that sell MTBE.

BUT, even the oil companies admit it reduces gas' energy per given volume by 3% +. This translates into about a 10% decrease in MPG. If you like to run your car at the track, never use MTBE blends, it will raise your e/t by a noticable difference.

I have no idea how the MTBE lobby got this crap into gas but they did. Since it's causing more pollution and is flawed science, I can only hope that anyone who produces the crap gets their pants sued off. I personally cringe when I see lawyers hit the scene, but this is one time I think they need to put some companies out of business. Some folks got very rich from bad science and our pocketbooks.

I also agree about the climate control someone mentioned. That can be an issue as well. My wife has a 2k2 Accord v6, and even when we use it for heat, the auto climate control turns on the AC. I guess that's to keep the cabin dry and clear of fogged windows but most of the time it's not needed. I always make sure to manually shut down the AC.

 

I remembered doing a paper on MTBE (methyl tertiary-butyl ether) during my college years. For anyone who is interested on this process...here is the link to the source. http://www.epa.gov/oms/consumer/fuels/mtbe/mtbe.htm

 

Mpg always drops in the winter months for me in PA...the colder it is..the worse it gets