Gas milage accuracy?
 

How accurate is the average milage display in the car? Mine shows 22.8 average. If I put it on instant it rarely shows 30 unless I an going down a hill. Mostly on the highway at 60 it shows in the high 20's.

I know when I refill the tank, the average is around 1 mpg lower then when I calculate the total Miles divided by gallons at fill up :confused:

My experience has been exactly the same as lvhhrpanel is describing.

Interesting. I routinely see 40 and 50 mpg stretches on slight downhill grades, routinely see the engine go into fuel cutoff mode (99mpg) on decent grades, and get plenty of mid to upper 30's on the flats. my DIC is showing 32.7 mpg overall, and was as high as 33.3 mpg until I had a spurt of rushed city driving last night.

It will be interesting to see where mine settles in once the engine is broken in and running with a belly full of synthetic oil.

UPDATE:

I just filled the HHR on the way to work today. I logged 33.8 MPG by the calculator, The DIC was showing 33.1 mpg. Not bad for a sub 1k mile engine in a combined cycle driving environment.

mpg
 

i found mine to be very accurate...within 1-2 mpg , and never more than 3 off...i used to check it daily , or every other day...i use just a little over a tank every 2 days...i allways used the same pump set on slow fill , then checked on paper and with calculator....i used to allways have my dash thingy set on instant...i just got tired of allways watching it....i still watch it , but i keep it on average now and reset it every time i put in gas , around 8 gal a day for 270 miles....the worse i ever seen it not match my paper/calculator was when i drive it real hard , testing my mods. ..i drove a double shift today , and watched it drop to 26 mpg:eek: , i was driving hard , with ac on , the traffic was heavy and i was in a hurry to get done..

Likewise.

My 2.4 HHR is very optimistic, it states that it is 23mpg when I calc it was 19. I changed out the gas and installed the intake/ecu upgrade so we will see how well it will look.

Just passed 10,000 miles on my 2009 and the DIC said 21.3 and I reset it for the next 10,000 miles. My calculation is 22.7 MPG. Good enough accuracy for me - I don't have any unrealistic expectations of technology.

My records for a 2800 mile trip matched the DIC average exactly.

taking mine to Bristol in a couple of weeks, nice long 1300 mile drive (one way), should be a good test of what kind of mileage I'm actually getting.