Question-------------------------
Followup To
Question -
I have a 1991 Fleetwood and the gas milege has been horrific. Ranging from 9.9mpg (city) to 15mpg on the highway. But an interesting thing happened. Just recently I forgot to put the gas cap back on after a fill up and I got 18mpg on that tank. So the next tank full, I left the gas door open & the cap off & got 24mpg. Not city driving on the 18 and 24, but not super highway either. Can you explain what is going on? I would like the problem solved so I can close the gas door and not look like "an old lady that has lost her mind". Thanks for any info that you can give.
Sally
PS: The car was given to me by a dear friend and meant to be a blessing.I have been driving it for over a year and the fuel bill has been very hard on my budget. Trust me, I am very thankful that I forgot the gas cap & will not put it back on right away, I am sure. Thanks again.
Answer -
This is ONE that I have NEVER encountered inover 25 yaers. I don't want to dis-believe yiou but this is totally impossible.
the only thing that can cause a SLIGHT reduction in fuel mileage is a problem with the emissions system.
I just plain don't believe that this DRASTIC improvement in fuel mileage is possible.
I think your calculations are WAY OFF.
I don't mean to be rude or disrespectful but this is literally imposssible UNLESS you posibly have a leak in one of the fuel lines when the system is pressurized with the cap on.
You need to get this vehicle looked at NOW.
autohelp
Responding to the above answer:
Thank you for your answer. I agree that it sounds absolutely insane. My mechanic is extremely reputable and he says that it is impossible also. But I really do know how to figure gas milege. 1.Fill the tank to full (let the pump shut off automatically & don't top off)) 2.keep track of miles driven 3.fill tank the same way, same place and same pump if possible (which I have done very consistantly)
4.divide miles driven by number of gallons it takes to refill the tank. Is that correct? Maybe I am doing it wrong. I have checked MANY times for a puddle of gas on the ground thinking I have a hole in the tank, but to no avail. The average milege on the tripometer is 50-55 when the F on the gas gauge dissapears & it shows 15 gallons left. That is when I am getting around 15mpg. When I got the 18mpg I had 72 miles on the tripometer when it showed 15 gallon mark and I had an amazing 91 on it when it showed 15 gallons. When I got the least mpg it only had 45 miles on the tripometer when it dropped from the F to 15 gallons. ? Thank you for your time and expertise in this matter. I have had my mechanic work on it. And like I said, he is very reputable and has a Cadi of his own. It was him & his wife that gave this one to me. They had never owned it, but took it in as payment for services done on something else. He is as confused with this car as I am. I will tell him what you said (& he certainly will agree that it impossible for the milege to vary that drastically) I am not sure that he has checked the gas lines for leakage. It was about 11 months ago that he worked on it and I just never said any thing more to him about it. Except when the mpg went up. Thank you for your time. If I ever get a definate answer (even if it is my mistake) I will let you know. Have a great life.
AnswerIf you are using the fuel mileage display gage that is on the dash, This is where you are going WRONG. This display is NOT accurate and is NOT to be used for fuel calculations. All this is basicall for is just another TOY that Cadillac should have been SHOT for installing it in the first place.
I have explained this to so many people over the years that I could literally scream.
To get an ACCURATE fuel mileage calculation:
1. Set the trip meter to "0".
2. Fill the gas tank and TOP IT OFF.
3. drive the vehicle until it gets down near empty.
4. refill the gas tank and TOP IT OFF.
5. Lets say you drove 350 miles and refilled the gas tank and TOPPED IT OFF and you installed 16 gallons of gas. This would give you an average of 21.87 miles per gallon.
You can also calculate your mileage by taking the mileage from the odometer AFTER you TOP OFF the gas tank. Let's say the mileage reads on your odometer as being 46118.7.
You drive the vehicle until the gas gage reads near empty and you refill the gas tank and again TOP IT OFF and you installed 18 gallons of gas in the tank.
Now your odometer reads 46412.8.
Therefore:
46412.8 Mileage on original fill.
-46118.7 Mileage on re-fill.
-------------
294.10 Miles actually driven
Your fuel calculation will then be 294.10 divided by 18 = 16.33 miles per gallon.
ALWAYS TOP OFF the gas tank when you fill it if your going to calculate gas mileage.
autohelp
