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Re: [RC] Diesel MPG - Truman PrevattWhat they read will depend on how they are programmed. However, most I've seen are programmed to take the running average over some number of miles - I believe I read somewhere that Ford uses 500. That is if I have been driving at 60 on the highway and not towing, it would read say 18 mph. Now I hitch up and start out and my actual mileage is say 12 mpg. For a long period of time - more than a tank or two of fuel it will read somewhere between 18 and 12 based on the average over the past 500 miles. It will read greater than 12 until it flushes out the higher mileage history. So if you depend on the miles to go to tell you when to get fuel your miles estimate will be too high (since it is using the average over the previous 500 miles). The reverse is true if you have come back from towing for a 1000 miles and then unhook and drive off. They are fairly accurate since they base the information on fuel flow (controlled by the truck computer) and speed (available to the truck computer).The best thing to do to get accurate reading from these instruments is to reset them often. That way you get rid of the long term memory that can bias them. I once had a car with a long term mpg read out from the computer and a instantaneous mph gauge under the speedometer. Boy you never wanted to look at the instantaneous gauge - especially if you liked to "goose it." Truman Milinda Ellis wrote: Jennifer is right on all counts! Another thing about watching your fuel economy the "old fashioned way" (that Jennifer described) is that you can sometimes tell when a problem is brewing with your vehicle when your MPGs drop (taking into consideration where you've been driving, how you've been driving (impersonating Shirley Muldowney, for instance), etc). It can also tell you if your fuel gauge is "off"... There's nothing like running out of gas/diesel and walking in the Texas summer heat, toting a gas can when your fuel gauge shows you still have 1/4 tank... When filling up our 1994 Chevy dually (now a lawn ornament, but that's another story...) the fuel gauge would shoot over way, way past "full". If you let it get down to below 3/8 of a tank, you'd better be sitting at a gas pump!!! -- "The opposite of a correct statement is a false statement. The opposite of a profound truth may well be another profound truth." Niels Bohr -- Nobel Laureate, Physics =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Ridecamp is a service of Endurance Net, http://www.endurance.net. Information, Policy, Disclaimer: http://www.endurance.net/Ridecamp Subscribe/Unsubscribe http://www.endurance.net/ridecamp/logon.asp Ride Long and Ride Safe!! =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
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