DECLINE IN GAS MILEAGE

[Ilovemyv8]

70k miles. Still getting 23 to 24 mpg.

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[H_Cons]

Haha everyone relax. I didn't think all caps would be such a big deal. It's kind of a habit for me because of work. Anyways I appreciate the replies. I am using the built in gauge and looking at total miles per each tank. It is summer so yes I'm using the AC more but this is my third summer having the car and I don't think I'm doing anything different while driving it. Only modifications I have are lowering springs and exhaust, which were both done when I first bought the car. I was thinking about taking it to the dealer to have them check the car. At point this I have no idea what the problem could be to be honest. Also, I use 91 octane and typically fill up at the same place every time.

 

[DickR]

Haha everyone relax. I didn't think all caps would be such a big deal. It's kind of a habit for me because of work. Anyways I appreciate the replies. I am using the built in gauge and looking at total miles per each tank. It is summer so yes I'm using the AC more but this is my third summer having the car and I don't think I'm doing anything different while driving it. Only modifications I have are lowering springs and exhaust, which were both done when I first bought the car. I was thinking about taking it to the dealer to have them check the car. At point this I have no idea what the problem could be to be honest. Also, I use 91 octane and typically fill up at the same place every time.

Any chance someone is siphoning gas from your car?

Have you checked the air fuel mixture gauge in the instrument panel to make sure it stays around 14?

 

[H_Cons]

Any chance someone is siphoning gas from your car?

Have you checked the air fuel mixture gauge in the instrument panel to make sure it stays around 14?

I doubt anyone is siphoning my gas. I typically only drive on weekends and I keep garaged during the week. I'll check the air fuel mixture when I get a chance. Thanks!

 

[Silver Bullitt]

Your mileage is pretty poor overall. Have you noticed if the car is running cooler than normal? Could be your thermostat is stuck open which will reduce your fuel mileage.

 

[draph]

How long since your last oil change? What is the oil level currently? Did you change it yourself, or do anything to verify the right stuff at the right viscosity was put in?

 

[Pony Express]

Potential exhaust leak?

 

[Interceptor]

Many areas have Summer formulations of gasoline, not sure if that applies to your area or not. People have reported performance differences between formulations for years.

This is most likely correct answer
I contantly monitor my MPG, never reset it. For last 10-14 days milage has dropped .5 mpg for no reason

 

[Cobra Jet]

Are you using the A/C more frequently? If so, it will reduce mpg’s.

Check tire pressures (when cold before driving).

Have you checked the condition of your spark plugs yet?

 

[Norm Peterson]

At point this I have no idea what the problem could be to be honest. Also, I use 91 octane and typically fill up at the same place every time.

I suppose you could pull and inspect the spark plugs.

I didn't think all caps would be such a big deal.

The Verdana font used by this forum (and many others) is proportional-spaced (letter widths as displayed vary). When you type Verdana in all caps, the spaces between the words are narrowed (a space is considered to be a relatively narrow letter) which makes the words look like they're ALLRUNTOGETHER (← exaggerated a little). Makes reading what you typed a task separate from the problem you want help with.


Norm

 

[DickR]

Many areas have Summer formulations of gasoline, not sure if that applies to your area or not. People have reported performance differences between formulations for years.

Usually winter gas combined with winter driving conditions result in lower gas mileage compared to mild weather. That said as I recall it has been extremely hot compared to normal on the West Coast recently so it might be taking more energy to keep the car comfortable.

https://www.bellperformance.com/blog/bid/49483/fuel-mileage-dropping-blame-the-winter-blend-gasoline NOTE: The writer made a typo part way down. Winter gas has lower energy content than summer gas as he states in other parts of the article.

You may notice that your gas mileage has gone down a little bit in the past couple of months. Before we go blaming on ethanol (even though ethanol’s been in the fuel all year), you might want to consider the little-known fact that “summer blend” gas is actually different from “winter blend” gas.

What’s this? Gas isn’t the same all year round? Well no, it really isn’t.

Gasoline formulators vary the composition of gas in the hot summer months and the colder winter months, in order to meet emissions and air quality standards. This “reformulated” gas is blended in such a way that it has a lower vapor pressure in the summer and a high vapor pressure in the winter blends. This means the summer gas evaporates less and thus contributes less to the “evaporative emissions” which represent million of gallons of gasoline per year evaporated in the air. Winter gas is more volatile and evaporates more quickly, so it is ideal for it is used in the colder air of winter.

In terms of gas mileage, you get better mileage on summer blends than winter blends because the summer blend gasoline has about 2% greater energy value than winter blend. So the gas you are using now most likely has a lower energy value than the gas you used in the winter. That means a little bit lower mileage for you until the spring time, when they will reintroduce summer blend gasoline. And this is beyond mileage loss you see with ethanol being blended into both summer and winter fuels. Cars, trucks, boats and small engines, all will see the difference in mileage and fuel consumption between the seasons.

Why can’t they just use summer blend gas all year round? Summer blend gas doesn’t work as well in the cold winter months because it is less volatile and doesn’t evaporate as well. This contributes to starting problems in the winter. Hence winter blend gas is prepared to eliminate this issue.

Can you avoid the summer gas/winter gas switch? Not likely if you live in California, New England or a major city of any appreciable size.

 

[DickR]

Also, the only accurate way to determine fuel mileage is to keep track of the actual miles per the odometer and calculate the mpg based on the amount of gasoline purchased. The trip computer in the car can be a decent estimate but accuracy varies from car to car from my experience so it is better to do the math yourself. Most of my driving life (since the 1960's) I recorded the overall odometer reading, the trip odometer reading since the last fill, quantity purchased, and the cost. I finally decided this year that I never really used the info unless I was concerned whether the car was "out of tune", etc. and now only keep track of major stuff since cars don't go out of tune anymore. Even old dogs can change.

 

[Bluemustang]

Your injectors might be a little dirty/clogged or your air filter needs to be replaced would be my guess. Put in some fuel injector cleaner when you fill up next time and then do it again on the second fill up. And change the air filter and do a KAM reset. I'll bet that will solve your problems.

Also look at your lead foot. You may be driving more aggressively than you're realizing. Still 10-11 seems a little even with a lead foot. I get that driving around down and idling alot when I am using E85, which uses almost 30% more fuel.

 

[TexasRebel]

10 is bad. My 140,000 mile F250 gets 13 mpg.

 

[NoVaGT]

I HAVE A 2016 MUSTANG GT PP. I JUST HIT 14K MILES THE OTHER DAY. FOR THE PAST MONTH OR SO I NOTICED A DECLINE IN MY GAS MILEAGE. I TYPICALLY DRIVE THE STREET AND A LITTLE FREEWAY AND I AVERAGED ABOUT 14-15MPG. NOW THE PAST MONTH MY AVERAGE MPG HAS DROPPED TO 10-11MPG. IM NOT DRIVING IT ANY DIFFERENT THAN BEFORE AND I HAVENT DONE ANY MOTIFICATIONS THAT MIGHT CHANGE MY GAS MILEAGE. I DIDNT GET A V8 FOR GAS MILEAGE BUT I THOUGHT THE SUDDEN DROP WAS STRANGE. HAS ANYONE EXPERIENCED THIS BEFORE OR KNOW WHAT IT COULD POSSIBLY BE?

IT WAS SUMMER, AND YOU WERE DRIVING HARDER. IT'S JUST YOUR DRIVING. MAYBE THE SUMMER BLEND OF GAS GETS LOWER MPGS. BUT THERE'S NOTHING WRONG OR DIFFERENT WITH YOU CAR.

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