Closing the Gap: How much does it matter?

Do not EVER trust instrumentation like that to be accurate unless you have VERIFIED it's accuracy with independent measurements. This is the real world, and in the real world, instruments have an accuracy range. It is based on the EXPECTED ERRORS from the manufacturing process. The majority get sold but not tested. Those errors show up in the sensor, variations in length of cable or tube or hose used, and in the mechanical device driving the pointer, or in the resistance to current flow in the case of an electronic device. SOME, but not all, of those instruments get tested to make sure they are in range, and if not get put aside and not sold (IF we are lucky). You can pick up 3 different instruments, and if you are LUCKY, one will read at the high end of accuracy range, another the middle, and the third at the bottom. All three are "accurate", but will give different numbers.

The bottom line, is do the math yourself and compare it to what you were getting on your dash, THEN use the dash number as an indicator of what your mileage is doing, but do NOT rely on it to be the one true gospel of fuel mileage. Shoot, I don't even trust the fuel level gauge to keep me from running out of fuel by itself. Ever.

 

Something interesting that I’ve noticed with the readout on my 579 is that if I drive for a while, or even most of the day, before I unload the dash will read higher than actual mpg. But if I sleep at or near the customer and I have an hour or so of pto time first thing the readout will show quite a bit lower than actual mpg.