Bad Gas Mileage - Advice

Long story short; my 2006 (NA) Legacy gas mileage has been getting worse lately.

 

When I first bought the car I was getting 500-550km (310-341miles) out of a tank. Now I'm lucky if I can go anywhere over 400km (248m) on a full tank.

 

What has changed?

 

Well, I'm running slightly wider tires in the summer. (245mm wide instead of stock 215). And I know that rolling resistance increased. I'm also aware that "winter gas" is worse, and thus the mileage during winter months gets worse.

 

Some background:

The car is a 5MT. Yes I drive it fairly aggressively. I know that your right foot dictates your gas mileage. BUT...

I know that I was getting over 330 miles out of my tank before, and now I can't get more than 250 under the exact same driving style.

 

Yes I take care of it and maintain it. Spark plugs are new. Air filter is cleaned regularly. Oil changes every 5000km (3000 miles) with synthetic, all other fluids are changed frequently, etc.

 

The only thing I can think of that would be causing this, is a clogged catalytic converter or a faulty o2 sensor. When I use Shell gasoline, the car throws a P0420 CEL. But the CEL disappears when I run any other brands of gasoline.

 

The car's computer is showing me an average of 10L/100km (23.5 MPG), and in reality there are days when it's more like 12L/100km (19.6 MPG).

 

This is definitely not normal, considering that I was getting far better mileage with the same car a year ago.

 

What other factors should I be looking into??

 

Thanks

You need to fill it and use the conventional method of going 200 miles, filling again and doing the math.

 

Everyone is complaining this year, I bet the fuel is the culprit. My mileage dropped from 22 to 20.

^^^ agreed. This miles per tank is complete bull sh!t.

I will try to do the 200 mile calculation and will report back to this thread.

However, it would be more accurate if I do this in a month or so. Right now it's still freezing cold where I live, and I idle the car for 2-5 mins every morning before I drive.

I personally fill up at the first quarter when I do city driving. That's usually around 70miles and enough gallons to avoid slight pump inaccuracies, but I also use the same station and pump for just about every fill.

 

Your winter time gas mileage will always be worse due to cold starts, all liquids are thicker when cold, plus oxyganated gas (might be different in Canada).

Don't let it idle !! That's the worst!

 

That's why your burning so much .

2 minute idle is healthy on a cold day with below zero temperatures.

 

 

EssTeeAai

Winter blend gas and idling to warm up reduced mpg by quite a bit.

I'm in Toronto (area) also and my mileage (kilometerage?) went down this winter too. I'm pretty sure its the brutal cold causing this. That said, I just drove back from Ottawa in good weather and I'm back to 7.6l/100km on the info centre display. Not spectacular by TDI standards, but for this car as good as it gets.

Yea idleing and short trips will burn a lot of gas .

Just cleaned the (K&N) air filter last night. Will have to clean the MAF as well, and see if that helps.

 

I also suspect that the gas we're being sold lately is worse than it used to be. (Not just the winter gas, but in general).

 

 

EssTeeAai

the car runs closed loop .. cleaning maf or air filter is not suppose to help unless there is something wrong with your car.

Just cleaned the (K&N) air filter last night. Will have to clean the MAF as well, and see if that helps.

 

I also suspect that the gas we're being sold lately is worse than it used to be. (Not just the winter gas, but in general).

 

 

EssTeeAai

 

You can buy 93oc everywhere in Toronto from top brands. You're still on winter gas but I bet your problem has nothing to do with any of that. It's been ultra cold which makes for longer motor warm up times.

2 minute idle is healthy on a cold day with below zero temperatures.

 

 

EssTeeAai

 

Says the man who cannot figure out why he has an MPG problem. No offense but you don't have a clue.

 

Start the car, remove any snow or ice and drive ASAP. You want high oil pressure and load on the motor.

 

Years ago when it would be -30-40c out we'd just start the car and drive it. We're talking late 80's early 90's. 5w30 dino oil. Never had any problems.

 

Any modern car is designed to be started and driven. So do so.

How often do you have to clean the air filter? I have that k&n flat air filter and I check it regularly, but the most I do is blow it out, which I see makes bigger air pockets. Is the filter cleaning kit a waste of money?

 

Also my exhaust leak from custom headers and a welded port of a 2 port cat for my rigged header setup really get the worse milage. Maybe opening up both ends of the cat isn't a bad idea

 

 

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you need the filter cleaning every 40-100k miles depending on conditions. that oil needs to be used annually for most people or it wont do any filtering.

 

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you can buy a more than life time supply in spray bottles and an aerosol for less than $20 on amazon.

the airfilter could be blocked completely if you engine is able to run it still use the same fuel.

 

a blocked airfilter would make your car better on gas as your maximum hp output would be less