Worse Gas Mileaage MPG - - SIGNIFICANTLY worse

Used to get a best of 430 miles to a tank of gas for Highway driving, averaging about 27MPG. Now, I am lucky to get 350 miles to a tank, which is under 22MPG.

 

MPG started going down about a year ago, I kinda though it was because the spark plugs were approaching 80k, but I pushed them a little further and replaced them about 8k miles ago and it fixed a CEL I had for cylinder 3 misfire, but it did not fix the fuel mileage. I am thinking of doing coils next since they have about 180k on them...

 

Car is an 05 wagon 5MT, BNR 16G, 850cc injectors, walbro fuel pump, turbo back exhaust, Grimmspeed EBCS, and other mods not relevant to issues too...

 

(Also to preface - I have another thread right now and my car won't crank, but thinking the fuel mileage/CEL issue might be related. But I had a CEL last week for cylinders 3 and 4 misfire, so had been planning on new coils next anyway. But now my car just won't crank, and thinking possibly coils 3 and 4 died completely and computer is keeping it from cranking)

To be honest, don't bitch. Don't even start. A 16G with bigger injectors and a tune really shouldn't be seeing more than 350 a tank, at best.

Haha, ya I've thought that myself, but seriously 430 miles to tank is what I used to get for the first 80k or 90k I put on the car!

 

Seems like a pretty significant drop though is why I think maybe coils?

seems a little weird I've notice a significant difference (drop) in gas mileage come winter then back to better gas mileage during spring time.

seems a little weird I've notice a significant difference (drop) in gas mileage come winter then back to better gas mileage during spring time.

 

Really? With my subie I've never noticed any difference in cold temps vs warm temps, BUT with all my previous cars (mostly american) I definitely got BETTER mileage in the winter time. After all cold air is more dense, more dense air contains more oxygen per cubic in.

There should be a difference between Summer and Winter blends, as far as mileage goes. You should experience a drop in mileage during the colder months when the Winter Blend starts hitting the tanks.

FWIW... I don't get close to 350 per tank with a VF52 on stock fueling. I probably should get a new tune. Unless tunes are like art... is mine more valuable now? I don't know. Someone help me with this.

FWIW... I don't get close to 350 per tank with a VF52 on stock fueling. I probably should get a new tune. Unless tunes are like art... is mine more valuable now? I don't know. Someone help me with this.

 

Shit, I'm lucky if I see 200/tank!

On a stage 1 OTS tune, my OBXT is lucky to see maybe 280 a tank... I drive roughly 80% highway.

350 to the tank isn't bad at all for what you're running.

 

Tris is right, there's a difference in summer and winter blends of fuel, you'll absolutely see worse fuel economy in the winter.

Im getting between 305-320 miles per tank currently on 93 octane shell winter gas with a stage 2 set up and cobb ots map(auto). I used to get 340+ miles per tank on my 06 sti stage 2.

 

 

Edit: I basing my number on my average mpg times fuel capacity not by tank average. My average mpg almost always stays at 19.8 on my legacy. Got it as low as 18 and as high as 23.7. For my sti I almost always stayed at and average of 23mpg. In any case my point is I can certainly tell that im filling up sooner in my lgt than in my sti. I only put $20-25 in at a time since I dont usually drive more than 100 miles per week.

Seriously don't listen to these nay sayers. Doesn't matter if your now getting what they consider is "normal", everyone's car is different and if your specific car got better mpg before and now it's getting worse, something is wrong.

 

Next, your miles to the tank measurement is as accurate as the weather channel. Your tank fill up in the warm could have been 14 gallons, while in the cold it's 15 gallons, that one gallon makes a huge difference in MPG. Per tank measurement is very inconsistent and is really just a guess, the only proper way to measure it is Miles driven / Gallons filled up.

 

Both of my Subaru's suffer a good 2-3mpg loss when temps hit below 60*F consistently, and it's not winter gas. I have couple hundred fillups between my two Subaru's overs the last two years in a spreadsheet. I haven't noticed winter gas blends make a noticeable gas mileage loss. What I have noticed is the cold weather killing my gas mileage due to longer engine warm up times, thicker fluids causing more friction etc.

 

 

Really? With my subie I've never noticed any difference in cold temps vs warm temps, BUT with all my previous cars (mostly american) I definitely got BETTER mileage in the winter time. After all cold air is more dense, more dense air contains more oxygen per cubic in.

 

More oxygen means more fuel needed to keep you at the 14.7afr. But it also does mean more torque, which means less throttle is needed to accelerate, but less throttle means your throttle plate is closed more thus you increase your pumping losses (less throttle = more vacuum = harder for your pistons to go up and down).

 

But, the best but of all, the real answer is "it depends". Every car is tuned by different companies and tuners with different agendas in mind. American cars you had before might be heavier, less aerodynamic, and engines weren't tuned to provide best torque at all temps, thus they struggled to keep moving while warm.

Tires? Brake dragging? Bad wheel bearings? Roof rack?

 

Are your injectors sticking open, flooding the cylinders?