So I am over 11000 miles on my G. I would roughly get 300 miles at approx. 16 gallons. Lately, it would seem it has gone down to about 260-270 @ 16 gallons. The air filter was super dirty so I said screw it and got a new one. Always use Shell 93 from the same station. Driving style is basically the same. Not quite sure what is causing the problem.

Any ideas?

 

First thing I thought of is maybe the MAF sensor is dirty. IDK.
Not an expert on all this electronic engine management stuff.
Another possibility could be low or lower tire pressure, which causes lower mpg.
About all I can think of now.

 

Take for what its worth
I read once where a guy put two and two together and came up with this...

he stated that when replacing a dirty air filter with a clean one with ultimately burn more fuel because with more clean air molecules passing the MAFS, it tell the master computer to pump more fuel into the mixture to compensate.
It made me think... Hmmmm?
But really, I found that sometimes subconsciencely I burn more fuel on sunny days than cloudy days...(in Ohio we only average 100 per year). I find myself giving it a bit more gas (higher RPMS between shifts) and whoops, I burn a little more fuel between fill ups... about the same difference you are getting.
just my $.02

 

I considered all of those. Tire pressure is always between 33-35 I never let it drop below that. The mass air might be dirty, but it seems to much of an immediate drop. A dirty mass will gradually decrease in mileage.

As for the sunny day scenario that is why I specified that I have not changed my driving patterns. Meaning no extra stomping on the accelerator. The exhaust does not smell any different meaning if it is running lean or rich.

I will probably reset the ECU to see if that works.

 

Depending on state, winter gas additives may reduce gasoline effectiveness 5-15%

 

Hmmmm...... that seems like a plausible idea. I am in NY as it is they supplement the gas with up to 10% ethanol. Before winter they stuff oxygen into it to make it run cleaner.

I will still have a go with the ecu reset for now, but this seems logical.

 

There's absolutely nothing wrong with your car. Winter gas is here and it has less BTUs per gallon than non-winter gas. If the temps have dropped then expect longer engine warm up which means prolonged rich A/F conditions. Expect to see a 10-15% drop in MPGs in the cooler months (sub 60 degree temps). My G has gone from getting a combined 21mpg to 19mpg in the past month after temps dropped into the 40s-60s.

For the winter, I recommend reducing as much sub 5-mile travel as possible and do as many errands as you can at once because you can really kill your mpgs in the winter. It wouldn't be uncommon for a G on a cold motor driving 1 to 3 mile stints to see 10-13mpg.

 

even with the MPG on this car, I have nothing but smiles. EVEN WHILE IM PUMPING my money into the tank... its just so damn fun

 

Thanks

 

Depends where your at if you have Winter gas or not. But even cold weather will make the car use more fuel normally. I know in Texas we do not get the Winter Gas here.

 

Am I the only one who's doing well on MPG around here? My 6MT has about 7700 miles on it. I'm doing 23-24 overall and it seems to be creeping up slightly with almost each fill-up, and I'm a fairly aggressive driver.

 

uhmm thats interesting..i never knew winter gas was different...good info

 

Are you do for a oil change? I normally get 300 mile per 17 gal and when the mileage comes near for an oil change, it drops to 270 per tank.

 

A 10% reduction in fuel economy from old (but still within specs) oil?
Consider the friction in your oiled engine bearings relative to all the other factors affecting fuel consumption like the car's mass, transmission/differential drag, rolling resistance (tires, wheel bearings & CV joints), brake pad drag, aero drag, accessory drag, etc. All other things being equal, your engine bearings would have to be compromised to the point of permanent damage in order to increase total fuel consumption by any measurable amount, let alone 10%. My $0.02.

 

^ Don't ask me buddy? I just fill the baby up. Regardless what season it is plus I live in SoCal where the weather's always warm, my mileage drops significantly around 2500k an oil change. I don't have a heavy foot or anything to abuse my ryde.