 » Site Navigation | | | | » Recent Threads | | | |  |  |  | |  04-30-2008, 05:40 PM | #1 | | Junior Member Join Date: Mar 2005 Location: Orange County Posts: 3 |  My MPG is suddenly down...
I typically get about 30 mpg, although all of a sudden I'm getting more like 20 mpg.
I don't know why.
I just had the oil changed and got a new set of tires put on -- so things are nice and smoothe... yet my mpg has been cut by 1/3.
Thoughts? |  |  | | 04-30-2008, 05:45 PM | #2 | | Senior Member Join Date: Sep 2007 Location: Malvern, PA Posts: 373 |
Any weird noises, rough idling? Listen closely for differences in engine sound. __________________
1997 TI Sport, Silver | | | | | 04-30-2008, 05:57 PM | #3 | | NOBODY F's with the Jesus Join Date: Oct 2006 Location: Ventura California Posts: 7,824 |
Look under the car for fuel leaks, check tire pressure, how old are your oxygen sensors? __________________ 4 MORE YEARS BABY!!! | | | | | 04-30-2008, 06:01 PM | #4 | | Senior Member Join Date: Aug 2004 Location: state college, pa Posts: 3,431 |
Tire pressure?
Also, did you change tire width/compound? __________________
I scream, you scream, we all scream for ZOMBIES. | | | | | 04-30-2008, 06:24 PM | #5 | | Senior Member Join Date: Sep 2006 Location: Wisconsin Posts: 1,895 |
After you check the tire pressure, check the air filter. __________________ ...
ʎɐqǝ uo pɹɐoqʎǝʞ ɐ ʎnq ı ǝɯıʇ ʇsɐן ǝɥʇ sı sıɥʇ | | | | | 04-30-2008, 09:04 PM | #6 | | Junior Member Join Date: Mar 2005 Location: Orange County Posts: 3 |
Thanks for all the replies!
The idling and engine noises are no different than ever...
I'll make a point to check the tire pressure later today -- and these new ones are the same size as the ones they replaced...
No leaks.
I'll have to ask the old man about the oxygen sensors...
Anyway, thanks guys for the input! | | | | | 04-30-2008, 09:37 PM | #7 | | Member Join Date: Feb 2008 Location: Frederick Maryland USA Posts: 45 |
Check your engine temperature. Thermostat failure shows up as lower operating temperature which will result in a richer than needed mixture and lower gas mileage. | | | | | 04-30-2008, 10:40 PM | #8 | | Senior Member Join Date: Sep 2007 Location: Malvern, PA Posts: 373 |
hmm. i think if you were getting an oxygen sensor failure your CEL would come on. can tire pressure really lower gas mileage that much? __________________
1997 TI Sport, Silver | | | | | 05-01-2008, 12:48 AM | #9 | | Junior Member Join Date: Mar 2005 Location: Orange County Posts: 3 |
Quote: Originally Posted by JNCoulombe  Check your engine temperature. Thermostat failure shows up as lower operating temperature which will result in a richer than needed mixture and lower gas mileage. | My temp guage is one thing I watch like a hawk, trust me. My first car was a Renault Fuego... let's just say it taught me some lessons.  Anyway, the engine temp is the same as always - it runs right at dead center of the temp guage... | | | | | 05-01-2008, 07:45 AM | #10 | | Senior Member Join Date: Jan 2008 Location: Milwaukee Posts: 189 |
Quote: Originally Posted by nyle hmm. i think if you were getting an oxygen sensor failure your CEL would come on. can tire pressure really lower gas mileage that much? | tire pressure can loser it quite a bit. I think they would have to be really low for that amount of change though. | | | | | 05-01-2008, 12:39 PM | #11 | | Member Join Date: Feb 2008 Location: Frederick Maryland USA Posts: 45 |
A poor performing, but not completely failed, O2 sensor does not necessarily trigger the code for sensor failure. I would certainly check tire pressure (costs nothing) and consider changing any of the usual suspects; air filter, fuel filter, spark plugs, and/or plug wires before changing the O2 sensors but that could be the cause. | | | | | 05-01-2008, 02:46 PM | #12 | | Senior Member Join Date: Aug 2003 Location: cary, nc Posts: 2,259 |
as for engine temperature, take note as to how long it takes to get to TDC.
my mileage dropped from 29 to 19 and it was the thermostat...the engine would be in the center....it just took forever to get there....thanks to a thermostat that was stuck open. replaced it and mileage jumped right up. __________________ 1995 318ti Active
Pioneer Speakers [] Aluminum Billet door locks [] ACS Pedals/Deadrest [] ACS Shift Knob / E-Brake Handle [] Clear Corners/Tails/Sides [] Sylvania Exterior Lighting [] Custom CAI [] Dinan Engine Chip [] Dinan Transmission Chip [] H&R Race Springs [] Tokico Illumina Shocks [] BMW X-Brace [] Relocated Lighter Mod [] Custom iPod Mod http://www.cardomain.com/id/robcarync | | | | | 06-29-2008, 12:08 PM | #13 | | Senior Member Join Date: Apr 2006 Location: San Diego Posts: 231 |
Try a different gas station, with prices this high, some of them are really watering it down. | | | | | 06-29-2008, 05:51 PM | #14 | | Senior Member Join Date: Apr 2006 Location: Oxford, Ohio Posts: 868 |
Vac Leaks... the boot at the intake is a bad culprit. Usually you have to take it off to see any holes. But there could be leaks in other places, so look around. | | | | | 04-09-2009, 09:01 PM | #15 | | Senior Member Join Date: Mar 2008 Location: Houston TX Posts: 309 |
If a thermostat is going bad can it really make MPG go down....I think the thermostat in my car is starting to go bad because it takes about 20 minutes to get to the center of the temp. gauge. And i can never get past 21.8 mpg. | | | | | |
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