So I picked the car up this summer, and it has 109.5k miles on it. So far he has ran very well and I've had no issues from the engine whatsoever, very solid idle. Recently, the temperature dipped down below 30's, and around this time, my mpg dipped as well. Earlier I had gotten around 25 mpg, and now its more like 18-19 mpg. What issues could cause this? Right now I think I'll put in some fuel system cleaners and see if anything gets better, if not I may take it in to get it looked at to be safe. Another thing I have noticed is that I get heat through my A/C vents, even though the A/C is off. I don't know if it is related, but thought I would throw that in. Thanks for any help.

 

Bought a 2003 R53 (Indi Blue) a year ago with 94,000 on it. 30,000 miles later (i drive a lot of highway miles) I average about 27 around town and 33 or so on highway cruising around 85. Cold weather does not help but you may want to do some simple things first: check tire pressure, mine had dropped to 25psi recently, air filter (I use a K&N), and plugs, coil pack, and wires. I replaced the old plugs with Champion rc318... Some will laugh at that but for under 10 bucks for four the copper plugs are more efficient in my opinion and plugs are easy to replace. Also had coolant replaced. Do you use premium fuel? Do you like to rev it high?

 

When cold, folks tend to use more power....the colder it is, the more hp you make with a SC, since the intercooler is so much more efficient....
Add that to the fact folks tend to idle their cars more....and cold idle is at higher rpms...a drop of some type is expected.

 

That's right ZippyNH. Cold air will drop mpg but gives good power as gearheads well know. I presumed his car was at good op temp and now notice he's in WA, can we factor in humidity if he's on the coast? Here in the Ohio Valley when the humidity hits mpg and performance lacks.

 

A good everyday mileage figure for mostly around-town driving in a R53 is 22-23. Fuelly's overall average for R53 mileage is around 25 which includes a lot of highway use, so these are consistent. So you may have just gotten an unusually high-reading initially and now are getting some low ones, both being just the noise due to driving conditions, pump shutoff, etc. And a small drop in mileage in cold weather is more/less normal. I'd take some more data before declaring a problem.

If by "AC vents" you're talking about the four large circular vents in the dash area, they're used for both heat and cold. There are no vents which are AC only.

- Mark

 

If it is an S model...I also find that the IC loves cold thus more power to the SC. If you city drive..like me...never out of 2nd gear....that will also contribute to low milleage...automatic or manual...

 

One more tip..sounds like you have automatic climate control...
With this the A/C is ALWAYS....so you can manually turn it off sometimes...and just turn it back on when needed (to stop windows from fogging).

 

P.S.
What tires (brand+size) do you have?
Some mini's have summer only tires...and that can cause some issues during the winter..cold, stiff rubber made for 70° summer days does not help mpg or general safety.

 

I'm not sure if Washington state does it but in Alaska, a Winter Blend is used starting in September or October. EPA federal regulations stuff.

It has a tendency to cause a drop in fuel economy. And as was mentioned, warm-ups are longer too. At least they are for me.

"...winter blend gasoline has a larger percentage of butane in it. And since butane is cheaper and has less energy, winter blend thus costs less and gives us a lower MPG when we burn it. So it’s a wash, right? Eh, maybe. Your vehicle miles per gallon typically will drop 2-8% when you start filling up with winter blend."

Source: http://itisscience.wordpress.com/201...-a-difference/

 

bjcarter hit the nail on the head. I get TERRIBLE winter mileage in all of my vehicles since moving to the PNW. My Tacoma dropped from 18 to 14 mpg, Scion TC dropped from 32 to 24, and my R53 just went from (city) 24 to 18-19. And considering how cold it doesn't get here - this irritates the crap out of me. Why doesn't the cost of fuel go down?!?!?!

 

If its not the cold weathers its usually the Oxygen sensor on its way out. You will get a sharp drop in MPG , then a little later you will get a EML light which points to a bank 1 or bank 2 failure. Which is the Oxygen senor before the Cat and after the cat.

There are some also great tips here with winter and the rear brake caliper sticking as well.

https://www.northamericanmotoring.co...sucks-now.html

 

Thanks for the replies guys. I live on an island, so humidity is always around. For tires I've got Pirelli RFT's, lots of tread left (I want to get them off for new ones..hate RF's)I believe I have the manual climate control..with the 3 dials in the center console. Most likely the car is just suffering from the cold and the longer idling, but I need to get a checkup on it since I haven't since I bought it.

 

air is also more dense in the cold, which requires more fuel to help balance out the Stoichiometry. that will drop, im ussually 28-29 in the summer, right now im sitting at 23-24

also the denser air is harder to push in your car, our cars are not as aerodynamic as some, then theres the winter blend of fuel

many things contribute

heat should be coming out of your vent, even tho it is on 0, air is still moving through for saftety reasons with refreshing air, such as if you had a CO leak from your exhaust, air would still be flowing through your car so you dont die. when you turn the blower on to 1-4 that actually starts the blower