Mileage Fluctuation

[sc72]

O.K. so here is the deal i own a 92 GL all stock except for the air box mod i did a couple days back, Thanks Tom and others, the deal is that the MPG's are changing with every tank refill and i always put 7 gallons in the tank, the mileage ranges from 25 to 38 mpg and anything in between, i have replaced the plug wires, cap and rotor, fuel filter, plugs on Monday and any thoughts on what plug to use. OK guys what are your opinions have i missed anything normal in the tune up line. Thanks

[freshtiva]

Temperature changes might make some difference but not that much. I assume your driving habits dont change that much. Do you buy your gas at the same place all the time ? Maybe someone is siphoning your gas .

[wybnrml]

Driving in the city and driving on the highway would make your mileage vary. Do you let your car idle to warm up sometimes, that would decrease your fuel mileage.

[ericsmith32]

Kraig have you replaced the o2 sensor, Denso only. Also get a can of throttle body cleaner and spray it around your vacuum lines. I had both on the Festiva and Aspire.

[crazyrog17]

How do you measure your mpgs? If you're always puting 7 gallons in, how do you know when to stop and calculate the mileage?

The gas gague can be very imprecise...

The way to do it would be fill it to the brim > Drive > Fill to the brim > Calculate MPG by how many miles you drove divided by how many gallons you filled up with.

[sc72]

Hello Shadran, your right, mpg's are better in the summer and less in the winter but this much change seems a little to much, ya i do get my gas at the same station 95% of the time, the last three tanks have been mostly road miles, mom is in the hospital in Des Moines and doing better so alot of road miles.

wybnrml, yes it does sit and idle but not more than maybe 5 minutes, do you think this would make that big of a change in mpg's.

Hello Eric, the car has aroud 140k on the clock so maybe it's time to change the o2 sensor, so the Denso is the one to have, ok it will get one. i'll give it a spray of either, probably just go buy a few feet of new vacumn line and replace. How is the wife and the pregnancy coming along. Karl

Crazyfrog17, i removed the gauge cluster and put a small white line down by the empty mark, when it gets to that point i put seven gallons in, read the trip meter and the odometer, log into a small record book in the glove box. I'll give it a try your way and see what happens, nothing to lose and i might just learn something.

Guy's i did forget to mention that the car surges as it climbs in rpm's between shifts i just ran out to the car and did the finger up the tail pipe test and yup i did get some black carbon on the finger. Any opinions about the brand of spark plugs to install.

[mattman]

the quality of fuel is crap here lately lots of methonal in all of it an water we have been tracking mpg in my wifeys hyndai an we run 120miles a night when we work out of town i was getting that to a quater tank an here recently it has now gone to almost a half tank 95% hwy miles driving at the same speeds an all car is in excellent tune tires are proper inflation ...i got a sample gallon from a local gastop an let it sit an it seperated into 4 layers after a few days so there has got to be somthing going on in the gas company looking for ways to charge more an spend less ...............at least thats what im thinking

[wybnrml]

wybnrml, yes it does sit and idle but not more than maybe 5 minutes, do you think this would make that big of a change in mpg's.

5 minutes won't make that much of a difference. But excessive idleing can decrease MPG, but I wouldn't worry about a few minutes.

[freshtiva]

? Maybe someone is siphoning your gas .

Off topic but a story:

A friend of mine use to live by a guy who always was talking about how much rain he'd get down at the local loafing spot everytime it rained. My friend started adding water to his neighbors rain guage when it barely rained and dumping rain out of it when it poured, guess their rain guages were on the same fence. Pretty entertaining my friend says. You dont have any jokers for neighbors do you ?

[sc72]

5 minutes won't make that much of a difference. But excessive idleing can decrease MPG, but I wouldn't worry about a few minutes.

OK thanks i'll take that off my list, but will remember to keep the idle time down.

mattman, just for giggles i'll clean out a Mayo jar and see what happens, might be interresting.

Has anyone done a milage test between Regular gas and the 10% Alcohol blend, any differance in performance.

[FestYboy]

^ i used champion, and later went to NGK, but the trick is to make sure they are copper core plugs, NOT paltinum or iridium.

[sc72]

Festyboy, NGK copper core, got it. thanks

Fresh, Levitan lives about fourty miles from me, so, well, naa, on second thought. Hows life down on the ranch other than the snow.

[Pu241]

Matt, Methanol is not DOT or EPA approved for motor vehicle fuel and is likely more expensive than ethanol.

sc72, hard to find just regular gas anymore around here. But, I would expect higher mileage because of the higher BTU content.
Also Temp does make a big difference in MPG, the colder it is the more heat is striped from the engine itself, which must be replaced or the engine does not operate at it's optimal temp. Also lower temps increase air density more than I would have at first thought, which make our already poor aerodynamics even poorer. check air density at say 80 degrees F and at whatever the temp you think you do most of your driving at.
I do not believe it will account for all your discrepancy but i believe is not insignificant.

[mattman]

my bad i was meaning ethonal not methonal my mind has been going 1000 ways all at once here lately so i sometimes scramble things a lil my bad on that thanks for the correction

[ericsmith32]

Hello Eric, the car has aroud 140k on the clock so maybe it's time to change the o2 sensor, so the Denso is the one to have, ok it will get one. i'll give it a spray of either, probably just go buy a few feet of new vacumn line and replace. How is the wife and the pregnancy coming along. Karl

My vacuum line was the one coming from the intake to the valve cover. Well until I ripped the one of the cannister yesteday. It may of been broke before I'm not exactly hee-man. Everything's going good so far going to the high risk doctors on the 14th. Ultrasounds every 2 weeks and every week after.