sunysb83

iTrader: (4)

ok, i've noticed my gas mileage has been decreasing over the last few weeks, i used to get about 24mpg and now i get 18mpg if im lucky, been doing the same type of driving of mix city/highway, i know that sounds average, but i think thats a dramatic decrease in gas mileage over the last few weeks. does this have to do with the weather being more cold? i've read the faqs so pls don't flame, but i would like to know how i can check if something has gone bad, there are no codes or 'check engine' light popping up for o2 or knock sensors. the car has 64k on it and i've bought it just under 60k, the previous owner said he just did a tune up and i've seen the receipt, but how do i check things like spark plugs, belts, fuel filter, fuel system, etc. to see if they need to be changed? these things should have been done with the tune up. i put my tire pressure 35f/32ri last changed my oil in sept with mobil1 and haven't even put 3k on the car yet since then. sorry, i love my max, but can't afford to keep paying for gas as that is the only thing increasing here.

Bobo

It would help to itemize what was done when the so-called tuneup was done.

1. Did they replace the spark plugs? If so, with what type.
2. Did they replace the air filter/fuel filter?
3. Did they replace the PCV?
etc

MaxKlinger

Bear in mind that as you're located in New York, you're now running "oxygenated" MTBE fuel. Per unit volume, oxygenated fuel contains fewer BTUs, or units of heat. The EPA admits that this does cause a mild loss in HP and fuel economy - they claim that a 3% decrease is to be expected. Personally I think that might be undershooting a little bit.

My fuel economy got crappy recently, too. I just changed my plugs and that helped a little. I think more of it is the fact that I'm letting the car warm up a little bit and defrost in the morning...that's zero mpg while idling.

Run a few tanks with STP fuel injector cleaner. I'm going to do that next.

Good luck!

Iqb316

I figure it's mainly due to the colder weather since it takes longer to warm up the car and also if you stop somewhere for like an hour, the engine becomes cold again, whereas in the summer, car was warmed up quickly and it would be still warm if you were to park it somewhere for an hour or two.
Just to be safe, you might want to run some fuel injector cleaner like MaxKlinger mentioned.

Terran

iTrader: (6)

Are you using the defrost on the climate control (the windshield blower option)? It uses the A/C to defrost. I noticed a decrease in fuel economy in my last full fill-up and I think that may be the reason. I had been leaving it on all the time, but since then I've been using it only when the windshield is fogged and changing as soon as it's cleared up. We'll see if it make a difference.

sunysb83

iTrader: (4)

thanks, im going to try the fuel injector. i always leave the ac on to circulate air when especially now when i turn on the heat, otherwise, all my windows fog up and i can't see anything, i dunno if that makes a difference. but is there anyway i can check if spark plugs and filters need changing? i hope its just the weather.
thanks for help

Terran

iTrader: (6)

Take off the AC and the recirc. Let some fresh air in and you won't need the AC most of the time (at least that's what I'm finding).

Dave B

1) Colder weather equals much longer warmups which kill your MPG
2) Gear oils are thicker which create more drag
3) "Winter" gas equals lower MPGs
4) Cold winter air can cause condensation in the gas tank which can put water in your gas and hurt MPGs.


I too noticed my MPGs plummeted in the past two weeks. I've gone from ~23mpg in combined driving down to about 20mpg.

MaxKlinger

Speaking of thicker oils, does anyone else switch oils seasonally? In the warmer half of the year I run 10W40, and in the colder months I use 10W30...not a big change, but it helps just a little bit with the increased viscosity in the cold.

Terran

iTrader: (6)

Nissan says 5w30 year round. At least use it in the winter.