802lexus

So when I got my 2002 sc430 it had 50k miles and I would get around 300 miles to the tank. Now with 60k I would get 250-270 miles to the tank. Can someone tell me why/how my car would loose 50-30 miles like that?

KBALL

I'm no expert by any means...but are tires underinflated now? Did you move and change elevation?
Have you tried some fuel injector cleaner? Did you start using a lower octane gas? Do less hwy driving? Have air filter replaced?

VVTiBob

KBALL is correct. There are too many variables to offer a definitive or reasonable explanation. To his list i'll add it could be as simple as adaptive driving...the SC's have a learning ECU which adapts to your driving habits/style. When you got the car the previous owner may have been less aggressive than you. Or it could be as simple as using the PWR switch which effects throttle and transmission.
You could test the latter theory by resetting the ECU and REALLY monitoring your driving habits for a few tankfuls. Although all of KBALL's suggestions are valid too.

Harold57

What time span are you talking about here? Gasoline chemistry changes with the seasons (typically there is a summer mix and a winter mix) and they perform differently. There is also the diference in loads between the seasons. During the winter, there is heavy use of the heater. During the summer, there is a very heavy use of the air conditioner (at least, here in Texas). During parts of the spring and fall, the a/c and heater are hardly used. That can affect your mileage. Have your driving habits changed? Do you have different tires now? (Different tires have different frictional qualities or drag on the road and will affect your mileage also.)

Another possibility is your oxygen sensor (or one of the other sensors) has gone out.

802lexus

thanks for all the help. i do have a aggressive driving habit. My tires are always inflated and i dont do that much hwy driving. i will check all of those things you guys have mention and hopefully it will be back to normal-ish haha

sebtown

Are you doing the math? or are you relying on the computer in the car? I do both and sometimes the car is as much as 3mpg off and other times the math and the car agree. I think it has it's own personality!

Jabberwock

Make sure tires are fully inflated. Clean your MAF, clean your throttle body, and make sure air filter is new/clean. These are simple to diy and likely to improve your millage a little. Put a couple of cans of Techron concentrate thru your gas.

You might also want to switch to a high quality full synthetic oil if you are running dino....that will also help a little.

That's about it - (assuming nothing is actually wrong with the car like a bad wheel bearing or a sticking caliper) making sure air and fuel systems are totally clean and tires are fully inflated, running full syn oil - all adds up to slightly better mpg.

GS4_Fiend

iTrader: (22)

change air filter and clean the MAF sensor. If the MAF sensor is dirty, you will get bad gas mileage period.