Unusual gas mileage situation

[gyrene81]

I have a 2003 Dodge Neon SE, 2.0 liter SOHC all stock.

Here's the situation. The car has 134,000+ miles on it with no major repairs aside from the radiator. Last year I did a gradual switch from conventional motor oil to full synthetic, now I use Mobil1 10w30 high mileage formula. Last May I put a set of Bosch quad fusion plugs in it. Just this past weekend I got a fresh oil change (after nearly 10k miles), new oil filter, air filter and plug wires. Ran 1 container of fuel system cleaner  through a tank of premium unleaded gas...I put 550 miles a week on the car.

Here's the rub...filled my tank this morning, I had 213.4 miles on the trip meter (gets reset with every fill up) since the last fill up...and only put 6.363 gallons of premium unleaded in it...that calculates to 33.5 miles per gallon!!!  The car is only rated at 29mpg brand new.

Has anyone else had anything like that happen without modifying the engine or doing a rebuild?

The only time I have ever had any vehicle get better than new gas mileage like that was after doing a full engine customization/overhaul...I'm not complaining but with my luck I'm waiting for the inevitable catastrophic failure... 

[APDrone]

Don't finalize your calculations on a single fill-up.

Run a couple tanks through and try to fill-up at the same pump.

Then see what you have.

 

[gyrene81]

Don't finalize your calculations on a single fill-up.

Run a couple tanks through and try to fill-up at the same pump.

Then see what you have.

 

Yeah you're right and that's the thing...prior to this last oil change I was getting consistent 30mpg.

[rpm]

So you went from 30 to 33.5? That sounds about right for switching to full synthetic and a tune-up.

[Strip]

Going from 30 to 33.5 mpg is only about 10% and can be attributed to driving conditions alone. A tune up and full synthetic is certainly capable of creating those results.

I ran four tanks of gas both before and after switching to synthetic myself, net result 1.3-1.4 mpg improvement over dino oil.

[CAP1]

I have a 2003 Dodge Neon SE, 2.0 liter SOHC all stock.

Here's the situation. The car has 134,000+ miles on it with no major repairs aside from the radiator. Last year I did a gradual switch from conventional motor oil to full synthetic, now I use Mobil1 10w30 high mileage formula. Last May I put a set of Bosch quad fusion plugs in it. Just this past weekend I got a fresh oil change (after nearly 10k miles), new oil filter, air filter and plug wires. Ran 1 container of fuel system cleaner  through a tank of premium unleaded gas...I put 550 miles a week on the car.

Here's the rub...filled my tank this morning, I had 213.4 miles on the trip meter (gets reset with every fill up) since the last fill up...and only put 6.363 gallons of premium unleaded in it...that calculates to 33.5 miles per gallon!!!  The car is only rated at 29mpg brand new.

Has anyone else had anything like that happen without modifying the engine or doing a rebuild?

The only time I have ever had any vehicle get better than new gas mileage like that was after doing a full engine customization/overhaul...I'm not complaining but with my luck I'm waiting for the inevitable catastrophic failure... 

my 93 geo prism averages 35+.

all stock 1.6L DOHC running regular oil, plain old champion spark plugs.

and i have a HEAVY foot.

[SEraider]

Are you taking it easier on acceleration due to milage?

Also, your tires at peak inflation?

[CAP1]

Are you taking it easier on acceleration due to milage?

Also, your tires at peak inflation?

me?

i run my tires at 35psi. i never take it easy in that car. my average cruise speed on the highways is 75mph indicated. there is some error in the speedo though.
 i'm used to 400hp v-8's, so i tend to have my foot in the floor on acceleration......till i get to my chosen speed.

 last year, i was running the a/c on the hotter days, but this year, i haven't needed it yet.

[gyrene81]

Are you taking it easier on acceleration due to milage?

Oh hell no...I'm an old geezer who grew up with modified big block engines, no such thing as "easy on acceleration"...


Before the switch to synthetic I was averaging 28.5 mpg...after the switch to synthetic it went to 30 mpg...now it's at 33 mpg...that's what has me confused here...I know this engine is loose and could probably use a top end rebuild so logically it shouldn't be improving...I drive a lot of highway miles at 73 mph...with a window open and the ac going...so I'm breaking all the rules for fuel conservation...

Also, your tires at peak inflation?

Yeah, I had the pressure checked and tires rotated when I got the oil change done...32 front 28 back

my 93 geo prism averages 35+.

all stock 1.6L DOHC running regular oil, plain old champion spark plugs.

and i have a HEAVY foot.

LOL Cap...you probably got the only one in the country that is good...might end up being a museum piece.  

[Shuffler]

Probably going downwind most of the time during this time of year.

[gyrene81]

Probably going downwind most of the time during this time of year.

LMAO... 

No such thing in Wisconsin...it's cross wind or head wind.

[CAP1]

Oh hell no...I'm an old geezer who grew up with modified big block engines, no such thing as "easy on acceleration"...


Before the switch to synthetic I was averaging 28.5 mpg...after the switch to synthetic it went to 30 mpg...now it's at 33 mpg...that's what has me confused here...I know this engine is loose and could probably use a top end rebuild so logically it shouldn't be improving...I drive a lot of highway miles at 73 mph...with a window open and the ac going...so I'm breaking all the rules for fuel conservation...

Yeah, I had the pressure checked and tires rotated when I got the oil change done...32 front 28 back

LOL Cap...you probably got the only one in the country that is good...might end up being a museum piece.  

lol....it'll never be museum worthy..........2 big dents, faded paint, headliner falling down, all that fun poop that tended to happen to early 90's poop-boxes....

 i just drive it for the mileage.

[Hornet33]

my 93 geo prism averages 35+.

all stock 1.6L DOHC running regular oil, plain old champion spark plugs.

and i have a HEAVY foot.

How "heavy" can your foot get in a Geo Prism? I thought putting your foot through the floor board was SOP just to get one of those things moving. That goes 0-60 in 20 minutes right??

[CAP1]

How "heavy" can your foot get in a Geo Prism? I thought putting your foot through the floor board was SOP just to get one of those things moving. That goes 0-60 in 20 minutes right??

nah...a little slower than that......0 to 60 in about the time it takes to eat dinner.


but that's WHY my foot's heavy.....it's the only way that car will out accelerate a lawn tractor. 

[Wolfala]

I forget who mentioned doing this, but i'll remember it as best I can. There was a guy who drove around the airport in a VW Rabbit with a diesel. Always bragging the mileage he got. A couple mechanics decided to screw with him - and would add a gallon everytime he showed up so his gauge would never move. During those times, they ask how many MPG you getting? Naturally the guy was quoting 70, 80 mpg and going up. Till eventually they started draining gas from his tank and giving him Escelade like mileage. Then the questions began, hows the MPG? The guy couldn't figure it out.