how accurate is the ditital mpg in the car. if we have a 20 gallon tank and i got 315 miles out of the tank then if im dividing correctly thats barely over 15 mpg. but my reading in the car said i was getting 22.7 mpg. any thoughts?

 

Mine's proven to be within about half a mile per gallon over about 3500 miles. Your calculation is off because you never use all 20 gallons of gas, unless you started with it completely full and ran it until it quit

Fill up the car, set the tripometer to 0. Run it until it's just about empty, then fill it up again. Record the mileage and divide it by the number of gallons you just put in.

 

What SteveZzz said. There's no way to determine how much gas you really used unless you run it from dead full to dead empty, or running from full and refilling to full. I have seen 450 miles of highway driving on a single tank, at about 27 mpg...after refilling, I found the car's estimate to be pretty accurate.

 

i dont think that digital one cannot be used to calculate total miles per gallon. it calculates how much you are getting at that time the reading was done... sometimes it gets a reading while i am in the parking garage and says that i am getting 9 mpg, and sometimes when i am driving down the street, i notice it says i am getting 18 mpg. i dont really use the feature for that reason.

 

it shows nine when stopped because it is an average from when you last reset it. it is pretty accurate. it bumps up to 18 when you drive because at that time you are probably getting like 23 or so. so the average increases. i reset mine at every tank. it is pretty accurate.

 

This is something I've wondered about lately with any car using any of these averaging meters. Let's say the car takes a sample (mpg, speed, etc.) every 1 second and averages that into it's running total. My question is, how many sample points can the computer store? 100,000? 1,000,000? If it can store 100,000 sample points, then the buffer would fill up after about 27 hours of driving and start overwriting the oldest data. 1,000,000 sample points would mean 277 hours of driving.

Basically, I'm just wondering what sort of buffers these things use.

 

if it is accurate, then that sucks because i am only getting about 14-15 mpg. i guess i am still breaking it in and i only do city driving.

yeah, how often does that thing take a sampling?

 

The buffer lasts somewhere between 6500-7000 miles. I'm not sure what the timer was on at that point though, so if it is based on time and not mileage, then I have no idea what the interval is.

I know this because I never reset my meter, except when the buffer fills up and the MPG all of a sudden goes to zero. I've had to reset the meter three times now (and the interval seemed consistent, but I'm not sure if it really was or if that was just my imagination), and I just passed 22,000 miles. I'll try to get a good mileage reading the next time it happens. I first time it happened was between 6000 and 7000 miles, and the second time it happened was between 13,000 and 14,000 miles.

I'm currently running 25.5 MPG in mostly highway driving.

-D'oh!

 

I reset mine every time I fill up and it does a good job. No complaints here.

 

This isn't true. It's pretty easy. Fill up the car and reset the trip mileage computer (odometer). Whenever you refill next time (at empty or quarter full or half full or whatever) use the mileage indicated by your trip computer divided by the amount of gas you just put in (at the end of your trip, not the beginning).

So for example, let's say you fill up on monday and reset the trip mileage computer. You drive around all week and on friday you are at 1/4 tank and your odomoter shows 280 miles since monday. You decide to fill up. You put 14 gallons of gas in. This means that you used 14 gallons since monday (since you were full then) and covered 280 miles. This equals 20mpg (280miles/14 gallons).

Of course the mileage may be inaccurate and the pump's meter may be off but my point is that other than instrument error, there is a very easy methodology for measuring mpg that doesn't require you to drive from "fully full" to "fully empty".

Jason

 

Who cares! Just drive it like you stole it and worry about gas later.

 

I've noticed that mine is a bit pessimistic, but is very close most of the time, usually within 1 mpg. I reset my meter every time I fill up the car.

 

hehe.. I wish we could do that hear in Oregon. Some of the stations here hit $2.35 for premium over the labor day weekend.

 

I average 15.6 mpg and it is all city driving. If I drive around in 6th gear, I can keep average about 1500 rpms, then the average goes up to 21 mpg.

 

That sucks! I guess we are somewhat lucky in Georgia. I can get premium for $1.50-$1.60. Still not cheap by anymeans though.