I'm getting around 15mpg

[Srmichi23]

94 lumina 3.1 with 30k miles on it. this two passed tank fulls i only just made it to 240 miles a tank if I'm lucky. i don't live in the city i drive on the highway to work everyday keeping it around 65ish, not really stuck in traffic since i go to work pretty early and come home early. I've read other threads about how much mpg people get and i only wish i could get as many miles as they do. any idea how i can better my mileage? or even better whats causing my bad mileage?

[Blue Bowtie]

How many gallons (not tanks or fill-ups) have you used over that 240 miles? I keep a notebook in my vehicles for recording gallons purchased and mileage. Using the fuel gauge and odometer is highly inaccurate.

[jfitzsi1]

Check engine light on?

[Srmichi23]

well when i fill up i get receipt for 13 gallons. hence leaving me with 3 gallons or so left in the tank when it marks E. during filling up i reset the odometer to check how many miles i will add up before it reaches E again.

check engine light is not on, only light that turns on is the overheating light on cold mornings but then slowly dims away.

[jrecken]

I have a 99 Buick Century with the same engine. I keep track of every drop of gas I put in the car and record the mileage every time. In the cold weather my mileage drops to 22-24 mpg. A month ago I filled up and the mileage dropped to what you mentioned. I filled a second time at the same gas station from the same pump and again the mileage was way down to 14-15 mpg. I was on a trip at the time and I was beginning to think something was wrong with the car although it was running just fine. I filled up again at a different gas station and the mileage went back to normal. I can only believe that it was just bad gas.

[Srmichi23]

ima try another gas station at next fill up and start to keep a log off miles and stuff.

By the way what should i be putting in my lumina, what octane?

[zuke448]

In regards to octane you should be putting on normal unleaded 87 octane. Running higher octane WONT give you better mileage. Dont waste your money

[GreyZ34]

I disagree. I use premium in my Z34 Monte and Z34 Lumina and get two to 4 mph using premium. It also starts easier better acceleration and more miles to tank. higher octane fuel burns hotter thus you do not need as much fuel to produce the same amount of hp and if you notice the computer can add more air to fuel burn process thus making it make more horsepower.
as for the mileage wow change stations see if that helps also listen to see if anything is missing when its idling or just coming off idle leaving a stop light.

[richtazz]

Originally Posted by GreyZ34

I disagree. I use premium in my Z34 Monte and Z34 Lumina and get two to 4 mph using premium. It also starts easier better acceleration and more miles to tank. higher octane fuel burns hotter thus you do not need as much fuel to produce the same amount of hp and if you notice the computer can add more air to fuel burn process thus making it make more horsepower.
as for the mileage wow change stations see if that helps also listen to see if anything is missing when its idling or just coming off idle leaving a stop light.

Higher octane fuel does not burn hotter, it actually is less volatile. Higher octane fuel resists detonation by being less apt to pre-ignite. Unless your car has a lot of carbon build up, there is absolutely no advantage to running high octane fuel in a car that doesn't need it. GreyZ34, both of your cars mentioned have the DOHC 3.4, which GM recommends running higher octane for peak performance (but it isn't required). The OP's 3.1 will gain nothing from running higher than 87 octane.

[Srmichi23]

k Ty for the info guys and i will try a diff gas station next fill up probably on friday so far almost 100 miles and it's half way empty

[Srmichi23]

well last night i changed gas station i decided to go to Shell and put regular at $1.71 a gallon. i fill up and went out for the night, this morning i went to the mall and back so far i have gotten 62 miles and the needle is still marking full

[Blue Bowtie]

Calibration of the pumps at gas stations is something which is usually only spot-checked, and is often driven only by consumer complaints. You might be paying $1.71 for a "gallon" of gasoline and only actually getting three quarts. You can check this yourself by filling a 5 gallon can for your snowblower and comparing the pump register to the capacity of your container. Don't be surprised if it is off by 10% or more.

[zuke448]

This is a possibility... Where I live in St Louis they have ethanol in the gas for emissions reasons and I seem to get worse mileage with the ethanol gas than I do with the non ethanol gas that I get while at school in Cape Girardeau. That is with every vehicle that I drive whether I drive my truck or the Lumina. It is always a matter of 2-3 mpg

[bigbadbronxy2k5]

OH man. I just calculated my mileage using this way: reset the odometer to zero @ fill up, fill tank to full and use Chevy's measurement of a full tank which according to my owners manual is 16.6 gallons. then drive till nearly empty and recheck odometer. 245 miles. That works out to 14.76 mpg. Ugghh . That sucks. BTW, no CEL, new air, fuel filter. PCV was changed as well, oil change done recently plugs and wires are in good shape. Car hauls a** like you wouldn't belive, so I'm guessing the converter isn't plugged. Car was a NYPD /FDNY car all its life so was well taken care of. It's a 99 9c3 w/ 3.8 and recently rebuilt tranny (well actually a new GoodWrench tranny was put in by FDNY 3 months before selling). No slippage and I added an external cooler and the fluid is new. Tires are properly inflated and brakes are new and free wheeling, lol, thought about brake drag. Had it happen to me on a Nissan Z once. Any ideas? And also I have found my Loomie runs different on 87 vs 93 Sunoco, which I always put in. 93 it runs quicker, and idles smoother. And during this test I was extremely lightfooted on it using mixed highway and city 55, max.

[zuke448]

Have you thought about carbon buildup on the intake? I know that GM sells a top end cleaner that removes all of the buildup on the intake where the stuff that you put in your tank doesnt reach. But the problem is that usually when you run that stuff in you will need to change the plugs because they will be black and black can get. Also you could be starting to have an injector leaking. I think that mine leaks as well.