Chevy Aveo Gas Mileage

whitefish · November 5, 2009

Hi Everyone,

I'm getting nowhere on the chevroletforum site with this, so I thought I would ask here.

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 - stock Ac Delco non-platinum/iridium with 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 to an horrible 350 to 380km 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). The spark plugs were pretty black (sooty) and smelled of fuel, so I think the car is running rich. MAF or oxygen sensor?

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

Any ideas....?

Thanks guys.....

desrtrat · November 5, 2009

what year Aveo do you have.. i have a 08 LT sedan w/ 5 sp and i use to get avg. 37-39 mpg with it. now i can sometimes only get 33 mpg with the same driving. i have taken mine to 2 different dealers and no one can give me a answered as to why. the first 10,000 mi i was getting 41-43 mpg. that includes a round trip from Ca. to NY city. i understand lousing mpg when we are forced Fed winter gas at 10% ethanol, but not the rest of the time..i'm at 28,000 now and when i get the chance i'll put pluge in and see what happens....

BTW.. no MAF on these motors

good luck

whitefish · November 7, 2009

Its a 2005.

For your mileage, is that US gal/mile or imperial? The best I EVER got was about 35 US gal/mile (about 42 IMP MPG). This is when I first got mine at around 10,000 miles, but it went down from there. I was amazed it jumped back up again to 42 MPG after the tune up!

I reset the computer by pulling the battery cable and I think mileage may be back up again (I haven't gone through a tank yet). Must have been an error code - all the more reason I need to get a scanner.

Nytemare · November 7, 2009

you may have an O2 sensor starting to go....just not enough out of tolerances to cause a CEL yet. That combined with winter fuel....mileage can drop a lot.

Make sure you give it some good Injector cleaner too....like Techron... it could have dirty injectors.

whitefish · November 7, 2009

Thanks. I did pick up some injector cleaner and I'm going to try it out. I thought about the O2 sensor too.

Nytemare · November 7, 2009

GM dealerships also have an intake cleaner that they snake through the entire intake to clean it out. And you could also try some Seafoam to clean the top end. That will help a lot.

desrtrat · November 7, 2009

Its a 2005.

For your mileage, is that US gal/mile or imperial? The best I EVER got was about 35 US gal/mile (about 42 IMP MPG). This is when I first got mine at around 10,000 miles, but it went down from there. I was amazed it jumped back up again to 42 MPG after the tune up!

I reset the computer by pulling the battery cable and I think mileage may be back up again (I haven't gone through a tank yet). Must have been an error code - all the more reason I need to get a scanner.

mine is US gal/MILES

GM dealerships also have an intake cleaner that they snake through the entire intake to clean it out. And you could also try some Seafoam to clean the top end. That will help a lot.

you can also use Deep Creep also from Seafoam and clean your throtle body while your at it..

good luck

whitefish · November 8, 2009

mine is US gal/MILES

Thats outstanding. So you are getting 450 to 500 miles per tank? I have a 4sp auto and I drive at about 60mph when commuting.

GM dealerships also have an intake cleaner that they snake through the entire intake to clean it out. And you could also try some Seafoam to clean the top end. That will help a lot.

When you say top end, do you mean down the cylinders or throttle body?

Never heard of Deep Creep, but I've been told to use GM Carb Cleaner on the throttle body of my 05 Silverado by a GM shop forman. Same idea?

Well, pulling the battery cable cleared something. Last tank was 500+ km.

Thanks guys. This site bets the crap out of chevroletforum. STILL no responses there.

Nytemare · November 8, 2009

By top end I mean the Throttle body, intake, valves, piston tops, and the top compression ring.

You pour the Seafoam/deep creep down the T-body modulating the throttle to keep the car going until it finally stalls out. You let the product sit for 10-15 min than start the car up and watch the smoke show. When all the smoke clears up your top end is clean as a whistle.

I know the Seafoam can be used in the tank to do a similar job and clean the entire fuel system, and it can also be used in the oil to clean out deposits right before you change your oil. Not sure if deep creep can be used the same way.

Just follow the instructions on the bottle for best results.

The fact that you got better economy after disconnecting the battery tells me that you may have a sensor going bad.

Unless you have an adaptive ECM that changes shift points etc with the way you drive...Do you have kids that drive your car??

whitefish · November 8, 2009

By top end I mean the Throttle body, intake, valves, piston tops, and the top compression ring.

Thats what I thought.

Unless you have an adaptive ECM that changes shift points etc with the way you drive...Do you have kids that drive your car??

Nope, kids aren't old enough to drive. Just the wife and I. I think its a sensor too. Losing almost 40% of my gas mileage in one tank can't be ECM related, can it?

Awesome, thanks alot. I'll give the Sea Foam a try.

Nytemare · November 8, 2009

It could be if you were flogging it...but not in one tank.

I don't know if these cars have the adaptive program at all...but having kids that flog your your car would explain some of your mileage decrease. But since that's not the case I would go with sensor...you just have to wait till it goes and throws a light.

The Seafoam or deep creep will clean the O2 Sensor also if its just dirty. Also, have a sniff of your exhaust to see if there is a "rotten egg" smell, this will indicate that you could have a catalytic converter going bad.

desrtrat · November 8, 2009

here is a link for Sea foam. just click on the product, and will explain all

http://www.seafoamsales.com/

the vid shows them poring the Sea foam WAY to fast with the motor running. i can't say why they did it that fast, but YOU CAN hammer lock a motor that way..i just let it suck out of the can slowly..

good luck

90454SS · November 9, 2009

If you know someone with an obd2 scanner you can watch the O2 sensor(s) activity. There is a range that the reading fluctuates and it can stay in the low or high range or proceed through that range slowly if there are issues. Then a good mechanic can trace where\what the problem is. Good luck!

whitefish · November 9, 2009

I do know a "retired" GM Tech (affected by GM's decision to close small delearships) - I'll have to see if he has a obd2 scanner. I'm thinking of getting a obd2 handheld or pc software anyways.

I would go with sensor...you just have to wait till it goes and throws a light.

Is it possible that an error code will be registered without the "Check Engine Light" going on?

Also, have a sniff of your exhaust to see if there is a "rotten egg" smell, this will indicate that you could have a catalytic converter going bad.

No rotten egg smell.

Nytemare · November 9, 2009

I would go with sensor...you just have to wait till it goes and throws a light.

Is it possible that an error code will be registered without the "Check Engine Light" going on?

It is possible, get it read...its fairly cheep. The Tech2 scan tool is probably your best bet though, like was said...it will check the O2 sensors activity and operating range.

Oh by the way, another sensor to check is the Air intake Temp sensor. Just plug a multi-meter into both connection points and read resistance. If its out of whack it will dump fuel into the engine as it thinks its colder outside and the engine requires more fuel. This sensor will not throw a code, as long as the resistance values are present...it will only code when the circuit is an open.