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View Full Version : BIG mpg DROP in car??? WHY


cbryan70
12-07-2007, 09:09 PM
I have an 02 chevy impala. In the past week or so i have notice my car has been burning ALOT more gas. meaning i was getting about 26 mpg and now its probably at 20 MAYBE. I realize it has gotten colder but i dont think i should have this dramatic of a mpg drop. About 3 weeks ago or so my check engine light came on, i checked the code it was low coolent "just had it tuned up" and it was maybe a half a a quart low so i added. And reset the code. Could this have anything to do with my big gas milage loss? any ideas what may be causing this?"

icewake
12-07-2007, 09:14 PM
I always see about a 4-5 mpg drop in my maxima. it kind of depends on how far you drive it becuase during the winter months the car runs much richer to warm up faster, im not sure how far you drive or anything but this could be a factor becuase the farther you drive the less decrease in gas mileage you will see

cdstukey
12-07-2007, 09:17 PM
Do you gas stations switch to ethenol for the winter? Gas mileage usually decreases when using ethenol or ethenol blended gas.

cbryan70
12-07-2007, 09:19 PM
ha our gas stations ALWAYS run 10 percent ethenol. Really that much richer icewake? Im only driving about 25 miles a day to and from work. And alot of times i will sit in my car during my lunch hour and take a nap. Could this really be affecting it that badly?

sand2snow22
12-07-2007, 09:20 PM
Shot in the dark, but sometimes when you have a bad CO2 sensor it causes the engine to run rich....

jwchapman
12-07-2007, 09:21 PM
Did the car overheat when the coolant was low? I had a time where the car overheated - overheating and burning the transmission fluid. Got much lower mileage until the transmission fluid was changed. Just a thought.

Leroy
12-07-2007, 09:21 PM
Are you running it during your lunch siesta and did not earlier?

icewake
12-07-2007, 09:23 PM
i say it would effect it some. i forgot about it but there is a lower restriction on how "clean" gas is during the winter months becuase it doesnt have as much effect on the atmosphere as the summer months. therefore during the winter months the gas is usually of a lower quality, not lower grade just quality. thats generally why you see gas rise during the summer months becuase it is of better quality so the companies charge more money. i could be wrong about all this but thinking about it and knowing a little about it its a possible reason

cbryan70
12-07-2007, 09:24 PM
no no problem with overheating. Ran at the same temp. Always been running it during lunch its either freezing here and need the heat or hotand need the AC not much of an inbetween! The car had a tune up at 100,000 and jumped up to about 28 mpg sometimes close to 30 for long trips on the highway but normal driving seems to keep it around 26 or so but lately for instance i burned a quarter tank in 87 miles and i usually get over 120 miles to at least the first quarter tank

cbryan70
12-07-2007, 09:25 PM
woudnt be an issue with gas quality we have heave smog regulations so gas prices in my area are generally more expensive then even 2 hours south of me. damn chicago!

icewake
12-07-2007, 09:27 PM
i visit chicago about twice a year and talking to my relatives up there they said it was very cold lately. if that is the case then when you do warm up your car its is using more gas, like i stated before. I am in tennessee and i recognize the difference due to weather changes

cbryan70
12-07-2007, 09:28 PM
yeah maybe the warming up the car a few times a day is killing the milage. I was thinking the ox sens to maybe i will have a loko at it

bigbird1031
12-07-2007, 10:20 PM
I dont think it is an o2 sens...i think it is a tradingvalve trade up to a toyota

cbryan70
12-07-2007, 10:28 PM
welp just filled up my car and only getting 17 mpg almost 10 mpg difference. any ideas

BoulderX45
12-07-2007, 10:58 PM
I would suggest you check the following; tire pressure and air filter also check to see if this car has a collant temperature sensor. This sensor, if not operating properly will set the fuel mixture rich to adjust to the cold temperature it is in or thinks that it is in due to the wrong readings. Some indications of this are hard starts when warm. I would also try and find out where your coolant is going? Is it leaking outside to the system or the inside of system like into the engine block itself.

Leroy
12-07-2007, 11:00 PM
Googled 2002 chevy impala gas mileage and seems this is within the range of mileage you should expect. Track over the next couple of tanks and note city or highway.

cbryan70
12-07-2007, 11:03 PM
coolant temp sensor i believe that is what set off my check engine light the first time. I have had full coolant it isnt leaking anywhere it was just a bit low from a coolant change i believe

cbryan70
12-07-2007, 11:04 PM
yeah well i havnt ever gotten 17 its been 20 AT THE LOWEST maybe never even that lowtill now i have the 3.4 engine not the 3.8

cbryan70
12-07-2007, 11:04 PM
how would i know if the coolant temp gauge was bad? is there a way to test it?

cbryan70
12-07-2007, 11:05 PM
Im not sure if it was the coolant temp gauge that was bad but it was somthing with coolant that set off my check engine light. would that be the one to do that boulder?

88 PS190
12-07-2007, 11:12 PM
I also notice a decrease, both with temp and with ethanol, midgrade in iowa is 10 cents cheaper a gallon than regular due to the ethanol in the midgrade, so I only run the regular till it gets cold, then sometimes the premium as I get stuttering sometimes out of my e30 running the regular and premium here has less ethanol than regular.

I would be sure to check the tire pressure, colder air = less tire pressure - worse economy.

cbryan70
12-07-2007, 11:14 PM
yeah im going to check tire pressure tomorrow. you guys run 30 E somtimes? wow we are always at 10 and then we have the E85 bs

JoshBuzz
12-08-2007, 02:34 AM
geez bryan, what're ya tryin to do? run up your post count?? haha you posted three times in two minutes!!

88 PS190
12-08-2007, 04:50 AM
I am in full support of E85, where else can you get 110 octane fuel that can be run through a carb for 2.8$ a gallon??? how else will you drag race and still not spend 400$ on fuel?

BUT! in cars it just plainly does not make sense! We make ethanol using corn and soybean mostly, which are both row crops. Which means we have fields for most of the winter/spring in barren soil which makes rain and melt runoff flow off through drain tiles and overground erosion.

This is not the best use for our soils!

Areas like brazil which can grow sugar cane (not a row crop) will not have the barren soil problem meaning less erosion and loss of fert.
Loss of fert means nitrates and phospates entering our waterways which leads to eutrophication and loss of usable ski waters!

My prefered methods... Diesels, for one diesels have higher energy per g/combusted than do conventional combustion engines (gas/ethanol) additionally biodiesels are able to be formed from waste and other sources (NO FREE LUNCH) we are after all going to form these things using Photosynthesis... meaning Light _ Carbon compounds _ energy... but along the way we need to conserve and prevent fert. run off into our waters!

BUT... ethanol burns more volume no matter what than gasoline, and most gas engines do not have the compression ratio or timing set up to deal with the shift in fuel types.

Some flex fuel vehicles can. Good luck for that.

TMCNo1
12-08-2007, 06:34 AM
People drinking corn liquor (moonshine) lose performance and mileage just like vehicles do, I'm just saying...........................http://www.gottadeal.com/forums/images/smilies/gd_tequila.gif

Maristar210
12-08-2007, 09:55 AM
People drinking corn liquor loose performance and mileage just like vehicles do, I'm just saying...........................http://www.gottadeal.com/forums/images/smilies/gd_tequila.gif:friday: :toast: :friday:

Maristar210
12-08-2007, 09:56 AM
Bryan,

I would think tire pressure might be down, air filter clogged letting the car warm up for periods adds up as well. Keep us posted and pay not attention to those Toyota folks 8p

TRBenj
12-08-2007, 10:54 AM
I always note a substantial drop in MPG this time of year. I dont know exactly what changes with the formulation, but Ive always been told that the gas stations switch over to a "winter blend." I see a corresponding increase in the spring when they switch back. All we have in this area is E10 year-round. Maybe a chemical engineer/gasoline expert could fill us in on the science behind it.

If youre seeing a 10MPG decrease, thats pretty dramatic. Ive always noticed about a 3MPG change. It could be the gas formulation change is compounding another problem. Sounds like you did a full OBDII scan- low coolant was the only code it threw?

JimN
12-08-2007, 12:09 PM
"during the winter months the car runs much richer to warm up faster"

Actually, the air density has a bit to do with how much fuel is needed and cold air with no change to the fuel will run lean.

Also, "winter blend" is different from "summer blend". Check the air cleaner, check your tire's pressure and re-check the coolant level.

cbryan70
12-08-2007, 01:00 PM
yeah that was the only code that it threw off

rick s.
12-10-2007, 01:49 PM
being from california I would suspect reformulated gas that we are supposed to burn in the wintertime. Supposed to be cleaner burning, but how clean can it be if you burn 15 to 20% more doing the same stuff you did before?

tommcat
12-10-2007, 01:51 PM
fuel mileage always drops this time of the year for several reasons.
1 is it's colder out and air is denser, denser air requires mores fuel to keep the same a/f ratio.
2 is vehicles take longer to warm up and run rich during this period
3 is people let their cars warm up in the mornings and never seem to take into account that while warming up in the driveway they are getting 0 MPG, which brings your average down quickly
4 is that fuel is blended differently in the winter months and this blend get worse fuel mileage.

you could also have a legitimate problem but more than likely it's just due to these factors

etakk7
12-10-2007, 02:33 PM
here in Minnesota they switch over to Winter blend as well and I notice the difference immediately. My wife's Pontiac Vibe and my Nissan Sentra both decrease about 3-5 MPG. 5 when it's very cold out, 3 if it's reasonable (ie. maybe 30)

Workin' 4 Toys
12-10-2007, 08:44 PM
I'd blame the catalytic converter.

cbryan70
12-10-2007, 08:47 PM
I'd blame the catalytic converter.
that clogged up on me right before the warrenty ended thankfully only about a year ago. Checked the tire pressure fronts were fine at a bit over 30 rear were at 28 bumped them all up to 30 or above

Leroy
12-10-2007, 08:48 PM
Hey Bryan, do you have a little brother that is 16 and just started driving? :D

cbryan70
12-10-2007, 08:49 PM
hahah that would explain alot...if i did he wouldnt drive my ****ing car!

TMCNo1
12-10-2007, 08:50 PM
I always run my tire pressure, 2 lbs. under max.cold on the front and max. on the rear.

Workin' 4 Toys
12-10-2007, 09:01 PM
that clogged up on me right before the warrenty ended thankfully only about a year ago. Checked the tire pressure fronts were fine at a bit over 30 rear were at 28 bumped them all up to 30 or above
I wonder if hollowing it out would help (I say don't do it)..... That stuff is like busting through solid charcoal though....(Not that I would know) I've heard.

A guy I used to talk with once in awhile had a buick (I don't recall year or model sorry) said his mileage went in the toilet slowly after about 150k(Keeping in mind he only lived less than a mile from where he worked). He had his cat. replaced and claimed to have his mileage back. Of course this in one guy, one car. No actual facts or documents. But I have (heard) what's in them, and I can't believe air (exhaust) actually passes though them.

What would it take to clog? And what problems would arise from it? I can't say for sure.

cbryan70
12-10-2007, 09:07 PM
when mine was clogged it was CLOGGED. No power in the engine reved high killed gas milage. And my car ran real hot. Happend on my way down to school out of no where. its a little warmer now so we will see.. since i refueled it hasnt been dropping as quickly as i havnt worked the past two days so perhapes alot of it has to do with idling in the cold weather. I wont do that this time around and see how it is.

Workin' 4 Toys
12-10-2007, 09:24 PM
Excessive idling....... It's the root of the problem IMO. Get the problem solved, and stop letting it idle so much. IMO.

cbryan70
12-10-2007, 09:34 PM
thanks for your guys help ill keep you posted

JimN
12-10-2007, 09:50 PM
With a one mile drive to work, there's no way it would be fully warmed up and running rich is a really efficient way to kill a convertor.

Workin' 4 Toys
12-10-2007, 09:58 PM
I've heard a 4.3 V6 with (what might have been) no cat. and a 40 series flowmaster...Sounded good I must say. I'd have to assume there is no chance of a clogged cat. with that set up.

Footin
12-10-2007, 10:20 PM
Oxygen senser?

damaged442
12-10-2007, 10:24 PM
I have an 01 Impala LS, I've got the 3.8 instead of your 3.4. 89,000 miles on it now. I notice the exact same thing you describe each winter. I normally run 27-29 mpg during summer, and 18-20 during winter. I just had the temp sensor go bad, had it replaced. I check tire pressure each week, and set it for 32 psi. Air filter is good, all other sensors good, mpgs bad. Just chalked it up to a winter thing. I wouldn't sweat it. Especially if you have any EtOH in your gas. It will make mileage suffer.

Footin
12-10-2007, 10:27 PM
My Avalanche has dropped also, in the summer I average 18.5 mpg and now with the colder weather it has dropped to 16.5.

Leroy
12-10-2007, 10:37 PM
Sounds like my sons who are sharing a car now.....

hahah that would explain alot...if i did he wouldnt drive my ****ing car!

MIMC
12-11-2007, 12:13 PM
Bryan -

If your mpg calcs are correct there is no way "winter blend" and "warm up idling" will drop your mpg by 10 alone. I'm assuming the car is warming up for 5-10 minutes. You already checked tire psi (32) and air filter. Is there a check engine light on now? How is the heat in the vehicle, does it crank out substantial amount of heat? I'm concerned about the coolant being low. 3.4's had have some issues with head gaskets and intake gaskets leaking - mostly externally. Please check your oil to make sure there is no "milkshake" look to your oil. If all the above checks out then I recommend getting a Tech 2 (or equivalent) scanner on it. Very possible you have a "lazy" O2 sesnor or coolant temp sensor - still functioning but barely and not falling out of parameters to set a code (check engine light). I'll do a bulletin search for ya and see if anything else comes up.

Lee in the "Big D"

damaged442
12-11-2007, 12:18 PM
Just brought this up to my brother, who works at a Chevy dealership, and he reiterated MIMC's words on the 3.4 having intake gasket problems. Apparently it is quite a popular problem.

cbryan70
12-11-2007, 01:19 PM
OHhh yeah already went the the intake gasket problem got it replaced. My car isnt running hot the heat is still normal temp. I think the coolant temp sensor was what set off the check engine light to start. loooked at it checked fluids put a little in and reset the code and it hasnt come on since. Would the Coolant temp sensor make the car get worse gas milage. there was alot more idling then just 10 min...about 40 min or so.

MIMC
12-11-2007, 03:58 PM
Bryan -

Whoa - is 40 minutes necessary? How many times a day? I don't know your situation, but I'm ready to retract my previous statement that "no way" is "blend" and "idle time" lowering your MPG's. :)

Regardless, without a SES light or diagnostic trouble code (DTC) the best thing you can do is connect a scanner and watch the performance of each particular sensor. Yes a weak coolant temp sensor can contribute to lower MPG's. Otherwise it looks like you addressed most of the common culprits that reduce MPG's. The cheapest way is to lower your idle time to 5-10 minutes and see if that helps. I did not see any technical service bulletins in our database that would possibly be related.

Thanks -
MIMC

cbryan70
12-11-2007, 04:00 PM
well since your online.. i have a knocking whe ni accelorate or turn. I beleive it is the intermediate steering shaft. Am i correct? i had this thing replaced when i got the car used and it is knocking. Is tha ta big deal? is it hurting anything?

MIMC
12-11-2007, 04:09 PM
Bryan -

Yea, I'm familiar with the i-shaft rattle! The noise is annoying but no concerns on safety, none at all. You have three options:

1.) Replace the i-shaft (I need to see if we released a new design for your application). If one is available it will be the most expensive option, but will be a permanent fix. Stay tuned.....I'll see if there is a new p/n.
2.) Apply the grease kit. Some cost associated with the repair, only a temporary fix, noise will come back in about 10k miles.
3.) Un-bolt the i-shaft at the steering gear, "stroke it" 3-4 times (take your mind out of the gutter for just a minute) :D and re-attach. Should last about another 6-10k miles before the noise returns. No cost, just a little labor.

cbryan70
12-11-2007, 04:35 PM
yeah not to worried about it. My gf's dad is a mechanic ill ask him how hard it would be to lube it up for another 10K. thanks for your help

cbryan70
12-27-2007, 03:44 PM
Well it was the coolent temp sensor that was causing the drop in gas milage. First run through with the new one and back up to 23

Bruce
12-28-2007, 01:57 PM
People drinking corn liquor (moonshine) lose performance and mileage just like vehicles do, I'm just saying...........................http://www.gottadeal.com/forums/images/smilies/gd_tequila.gif

Not me. If it is double and twisted with a good bead it will make you rich, good looking, and out of debt! I also have also been told my I.Q on occasion approached genius level, I was the funniest man alive and the coolest dancer ever. That of course was in my youth.
Bt the way Harold as a kid I ran shine from Hendersonville N. C. to Greenville S.C. (down the mt. no lights at night) Guess I am o.k. with statue of limitations.

TMCNo1
12-28-2007, 02:03 PM
Not me. If it is double and twisted with a good bead it will make you rich, good looking, and out of debt! I also have also been told my I.Q on occasion approached genius level, I was the funniest man alive and the coolest dancer ever. That of course was in my youth.
Bt the way Harold as a kid I ran shine from Hendersonville N. C. to Greenville S.C. (down the mt. no lights at night) Guess I am o.k. with statue of limitations.


Stories like that I like to hear, way to go! Just think, you could have been another Junior Johnson and made a fortune in NASCAR!:rolleyes:

Bruce
12-28-2007, 02:23 PM
Stories like that I like to hear, way to go! Just think, you could have been another Junior Johnson and made a fortune in NASCAR!:rolleyes:

If only I had had a good manager. I had the car! (My dad's 1949 Ford) It would flat haul! Many moons later(no pun)When my Dad would come to visit me here in La. He would always bring me a qt. of "shine". He always got the best. He got it from the sheriff! Talk about smooth!( the bad stuff which used red devil lye to work it would hurt you!)

TMCNo1
12-28-2007, 02:39 PM
If only I had had a good manager. I had the car! (My dad's 1949 Ford) It would flat haul! Many moons later(no pun)When my Dad would come to visit me here in La. He would always bring me a qt. of "shine". He always got the best. He got it from the sheriff! Talk about smooth!( the bad stuff which used red devil lye to work it would hurt you!)

Or the old brass lead soldered car/truck radiators used as condensing units!!!!!!!

I knew a prominent NASCAR/Winston Cup personality who, as late as 1995 was hauling 300 gallons/week out of Wilkes County, NC in a 1965, 289c.i. restored Mustang that had 8" thick rear springs at the axle. He also owned a 1940 Ford Deluxe Coupe Street Rod (yea, sure) with a 358 c.i. Winston Cup engine, running gear, suspension, brakes built by JJ, that he drove to Wilkes County occasionally.
That is some sweet stuff, just hours out of the cooker! I haven't had any since he passed away of natural causes!

JBaker
12-28-2007, 02:52 PM
Guess I am o.k. with statue of limitations.

Hey Bruce! Statue of limitations, eh? Is that like a sculpture of limitations? Sorry, had to bust ya!:D

Bruce
12-28-2007, 03:02 PM
Or the old brass lead soldered car/truck radiators used as condensing units!!!!!!!

I knew a prominent NASCAR/Winston Cup personality who, as late as 1995 was hauling 300 gallons/week out of Wilkes County, NC in a 1965, 289c.i. restored Mustang that had 8" thick rear springs at the axle. He also owned a 1940 Ford Deluxe Coupe Street Rod (yea, sure) with a 358 c.i. Winston Cup engine, running gear, suspension, brakes built by JJ, that he drove to Wilkes County occasionally.
That is some sweet stuff, just hours out of the cooker! I haven't had any since he passed away of natural causes!

Harold hope we can meet one day. Man, could we talk! By the way my wife's first cousin was married to an old time racer-Buck Baker and she was a Miss Darlington 500.
You are right on about the radiators. (Wonder where a guy could find a good worm these days?) Also ran from Tuxedo and Flat Rock. I was a Junior in High School and making what was big bucks in those days.

Workin' 4 Toys
12-31-2007, 08:37 AM
Well it was the coolent temp sensor that was causing the drop in gas milage. First run through with the new one and back up to 23
Good to hear.;)

Bruce
12-31-2007, 12:36 PM
Hey Bruce! Statue of limitations, eh? Is that like a sculpture of limitations? Sorry, had to bust ya!:D

Oops, Is there another t there Vanna?

sc00ter_17
07-27-2008, 02:18 AM
I have a 99 Pontiac GTP slightly modded with a smaller supercharger pully reprogrammed PCM, Cold air Intake and some exhaust mods and I am getting 28 MPG in summer and 24 in winter running 93 Octane ethenol fuel (Milwaukee). Smokes the tires rolling at 30 MPH. Almost as fun as power turns!!:)