Aveo Gas Mileage - Good then not so Good

[whitefish]

I recently read a post on ways of improving fuel mileage on Chev Aveo's. As per the post, I replaced my air cleaner (which was a fairly new OE GM air cleaner) with a K&N filter and a set of new spark plugs. The old stock air cleaner looked okay, but the spark plugs were BADLY eroded (about 70k on it at the time). Mileage jumped from about 350km per tank (mostly highway miles) to over 500km per tank (sometimes over 550km).

My mileage is starting to drop again to around 400 to 450km per tank. I cleaned the K&N air cleaner (as per instructions and replaced filter oil) and checked the plugs. Some slight erosion, but still in spec (0.044 inch gap).

My only thoughts are that mileage would be dropping (now down about 20%) due to the change in temperature - I did the tune up in summer when the temp was about 25C and now its about 5C.

Any ideas....?

[whitefish]

Anyone....?

[Daox]

Winter mileage will always be lower. Your mileage should be increasing now that its getting warmer out. Wait it out a few more tanks and keep track of your mileage to be sure.

[whitefish]

I agree that winter has an affect on fuel economy and I do see my fuel economy rising now that the temps are above freezing. Problem is, I did the tune up (K&N air filter and plugs) last May and watched the economy go down in late summer/early fall - well before winter. Then it went down slightly more in the winter.

I have noticed that when I do an ECU re-learn (aka, pull the battery cables), my fuel mileage goes back up, but then back down again after one tank. No CEL has come up, but I haven't check for error codes. I'm wondering if it isn't the O2 sensors, but I haven't got around to checking them.

[petrified.rabbit]

If it's good after disconnecting the battery it might do worse as it learns your driving style? How do you typically drive? The car could be running lean during the learning curve giving you the extra mileage.

Converting that though you sound really low with typical driving is that Mostly city?

[whitefish]

Most of my driving is commuting back and forth to work on the highway at about 100-110 km/hr. Some limited city driving. As I said, with the same commute, same driving style and just the replacement of a filter and plgs (I didn't remove the battery cables for that, so no ECU reset), I jumped from high 300's to mid 500 km per fill up (I do calculate by odometer and litres per fill so that I do calculate this more precisely). After a few months, mileage started to go down again.

I've tried varying my driving style, changing where I fuel up, and two treatment of GM fuel injection cleaner. Noting has significantly changed my fuel ecomony.

[Daox]

You need to actually log your mileage if you want to analyze things. KM per tank is just about the least accurate way to measure things. Your gas gauge is pretty inaccurate. Its basically there just to tell you when the tank is getting low. I suggest logging your miles driven and gas used at each fill up and calculate the mileage manually. Its the only way to know for sure what the mileage is. From that you can see what you are getting versus what you are supposed to be getting per the EPA and go from there.

[whitefish]

You need to actually log your mileage if you want to analyze things. KM per tank is just about the least accurate way to measure things. Your gas gauge is pretty inaccurate. Its basically there just to tell you when the tank is getting low. I suggest logging your miles driven and gas used at each fill up and calculate the mileage manually. Its the only way to know for sure what the mileage is. From that you can see what you are getting versus what you are supposed to be getting per the EPA and go from there.

Thats precisley what I do:

(I do calculate by odometer and litres per fill so that I do calculate this more precisely

What I should have said is "trip odometer". I don't have my Mileage Excel spreadsheet on this computer, but I have tracked fuel consumption per km/mile since I bought the car, based on the method you suggested. It has definately varied substantially. I'll look at the numbers tonight and post some examples.

[Daox]

Woops missed that.

Yeah, post the numbers up and we'll figure stuff out.

[whitefish]

Woops missed that.

Yeah, post the numbers up and we'll figure stuff out.

Not a problem. Okay, here are some numbers. These will be in a litres/100km, Miles/US Gallon and, Miles/Imp Gallon. All numbers reported are primarily highway miles.

The BEST mileage I ever had in this car, was shortly after I bought it in 2006, which was 6.73/34.94/41.97
The worst ever highway mileage was 9.81/23.97/28.78 in January 2010. The mean temperature was around -19C

RIGHT before I did the K&N filter/spark plug tune up in spring of 2009 it was 9.61/24.46/29.38

RIGHT after I did the K&N filter/spark plug tune up in spring of 2009 it was 7.97/29.50/35.43

It was up to 7.44/31.61/37.7 at one point.

By October/November 2009, I was averaging 9 litres/100km (26 miles/us gallon).

Just to show this isn't seasonal, I was routinely getting 7.8 litres/100km average (30.2 miles/US gallon) in January of 2007!
The mean monthly temp that year was -16C