In the past 2 weeks I have noticed i have lost about 35 miles off a full tank of gas...I normally get about 200 miles per tank...I have not modified the car at all in the past 3 months and I would be interested to hear any opinions on what could be causing this and if there is anything I should check..the only change is that it has been very cold in the past 2 weeks other than that no changes in the way i drive.
Decrease in gas mileage =[
- Thread starter jcori1
- Start date
wmburns
SN Certified Technician
Quick suggestion. Clean the MAF. Use MAF cleaner.
Next, consider replacing the O2 sensors if over 100k miles. As they age, the O2 sensors response time slows. This slows the PCM's reaction time to changing conditions resulting in less than ideal operation (decrease in fuel mileage).
Check for vacuum leaks.
Check the spark plug wells for moisture.
The usual stuff follows. Spark plugs, air filter, fuel filter, air pressure, dragging brakes......
Next, consider replacing the O2 sensors if over 100k miles. As they age, the O2 sensors response time slows. This slows the PCM's reaction time to changing conditions resulting in less than ideal operation (decrease in fuel mileage).
Check for vacuum leaks.
Check the spark plug wells for moisture.
The usual stuff follows. Spark plugs, air filter, fuel filter, air pressure, dragging brakes......
ChillPhatCat
20+ Year Stangneter 
Have you actually calculated your mileage or are you just going off of the gas guage? Next time you should record how many miles you put on since your last fill up and then divide that by the number of gallons it takes to top off your tank. Chances are it's just the cold weather startup and other things that make cars less efficient this time of year. You should always calculate the actual mileage instead of guessing from highly inaccurate guages that come in just about every car. Variances of 2-3 mpg are pretty common between seasons.
Thanks for the suggestions...ever since i bought my car about 2 1/2 years ago completely fill up my tank from empty and reset my tripometer...so i usually get about 200 miles to a full tank...sometimes i see a decrease of 10-15 depending on different factors...but this by far has been the biggest drop and it made me nervous....after i top it off the tank my needle usually doesnt go below the full line until i put about 24 miles on the car...i put about 22 miles and the needle is between 3/4 and full...I am going to do one more full tank and see how many miles i get out of it and if it stays with the problem I am going to have to really do something about it
ChillPhatCat
20+ Year Stangneter
patman0911
Founding Member
Track it for a few fill-ups and see if it's a trend or if it's just one off tank. And yeah, actually write the mileage and gallons down and do real math.
My MPGs dropped off pretty starkly with the onset of cold weather and I suspect the changeover to winter gas blends a couple of months ago. It's gone from my usual 18 MPG to a consistent 15.
My MPGs dropped off pretty starkly with the onset of cold weather and I suspect the changeover to winter gas blends a couple of months ago. It's gone from my usual 18 MPG to a consistent 15.
With the temperature dropping over the last month, i can think of at least 3 reasons.
1. Colder environment means unless you have added air, your tire pressure will be lower, resulting in lost fuel economy through increased rolling resistance
2. Colder environment means air is denser which raises the total aerodynamic drag (not to be confused with your drag co-efficient). Your car has to do more work to push the air out of its path
3. Colder environment, especially in ice and snow, means your tires never reach normal operating temps which further increases their rolling resistances.
4. So many other things that could have happened that I can't think of.
If you are seriously concerned with your fuel mileage, the best way to improve it is to remove as much restriction in both the intake and the exhaust path. Get it tuned and specifically tell the tuner you want an economy tune added. Add tires with lower rolling resistance ratings. On top of that, if you have aftermarket gears over 3.55, adding a 6 gear with a .50 ratio will do worlds for your mpg. Even with everything I have done to my car including the supercharger, I will still get over 30 mpg on the highway. At 200 miles, I am barely under 3/4 of a tank which is still stock size. if you have questions, let me know.
1. Colder environment means unless you have added air, your tire pressure will be lower, resulting in lost fuel economy through increased rolling resistance
2. Colder environment means air is denser which raises the total aerodynamic drag (not to be confused with your drag co-efficient). Your car has to do more work to push the air out of its path
3. Colder environment, especially in ice and snow, means your tires never reach normal operating temps which further increases their rolling resistances.
4. So many other things that could have happened that I can't think of.
If you are seriously concerned with your fuel mileage, the best way to improve it is to remove as much restriction in both the intake and the exhaust path. Get it tuned and specifically tell the tuner you want an economy tune added. Add tires with lower rolling resistance ratings. On top of that, if you have aftermarket gears over 3.55, adding a 6 gear with a .50 ratio will do worlds for your mpg. Even with everything I have done to my car including the supercharger, I will still get over 30 mpg on the highway. At 200 miles, I am barely under 3/4 of a tank which is still stock size. if you have questions, let me know.
patman0911
Founding Member
Another side effect of cold, dense air is that pumping losses are increased at cruising since it takes less throttle opening to allow the same mass of air into the engine.
Between the temps in the teens and 20's, long periods of idling when checking for leaks after my intake swap and lots of bursts of WOT acceleration enjoying the results of my intake swap, I'll be lucky to crack 200 miles on this tank
Between the temps in the teens and 20's, long periods of idling when checking for leaks after my intake swap and lots of bursts of WOT acceleration enjoying the results of my intake swap, I'll be lucky to crack 200 miles on this tank
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