Trip mileage computer

[TFlewitt]

I am looking for an '06 DRW 3500 and noticed that the trip computer only has average fuel consumption, not average and instant like the '01 trip computer I have. Does anyone know if any of the 3rd generation years had the instant fuel consumption feature? I find it really useful for finding the sweet spot for towing. Thanks!

 

[rbattelle]

None of the 2003-up trucks have the instant fuel economy display.

Ryan

 

[Motorhead]

I liked the one on my '01. 5 also. I used it like a vacuum guage is used on a gasser. When I towed, I would pull out of OD when the instant got to 10mpg.

 

[TFlewitt]

I wonder if the chip has the capability, but was just not enabled for some reason. Looking at the L. E. D. display on a '99 and '01 computer, the display is the same - both have the instant readout capability, but the '99 will not actually display this data. I will perhaps have to look at the chips to see if they are the same or not. Anyone know if this feature could be enabled on the 3rd gen computers?

 

[betterthanstock]

The 03, after you reset it, shows your instant mpg, but you lose the long term. It averages from the last reset. How does yours react, after you reset it?

Otherwise, a strictly instantaneous mpg is worthless, since it changes drastically second by second, with every bump of the throttle/cruise control, and every hill and wind gust, so you still need to average over a mile or two, to get any meaningful number.

 

[TFlewitt]

Trip computer

I guess if you haven't used the earlier trip computer with both instant and average functions, it is hard to explain. No, it is not useless, but in fact very useful. There is some slight delay programmed into the instant setting, but no, it does not change drastically second by second. After reset, the average setting works like yours, the instant setting continues to show current fuel consumption. Very handy for towing and testing.

The 03, after you reset it, shows your instant mpg, but you lose the long term. It averages from the last reset. How does yours react, after you reset it?

Otherwise, a strictly instantaneous mpg is worthless, since it changes drastically second by second, with every bump of the throttle/cruise control, and every hill and wind gust, so you still need to average over a mile or two, to get any meaningful number.

 

[betterthanstock]

I guess if you haven't used the earlier trip computer with both instant and average functions, it is hard to explain. No, it is not useless, but in fact very useful. There is some slight delay programmed into the instant setting, but no, it does not change drastically second by second. After reset, the average setting works like yours, the instant setting continues to show current fuel consumption. Very handy for towing and testing.

I have driven a borrowed car with instant mpg way back in the 80's, when they first came out, and I own one now with instant mpg. The instant mpg just follows your right foot. The only difference with the average guage is that you need to reset maybe 10 times, to find your sweet spot.



Now some people are obsessed with the mpg guage, and slow down uphill, for fear of seeing really low numbers (like you don't see 0 mpg at all stoplights-- is 5 mpg any worse than 0?), and speed up downhill, because the gauge "allows" them to speed with no apparent mpg penalty. That is not true. The average mpg is best if you don't speed downhill, as long as you don't use your brakes, and if you don't slow down uphill, as long as you do not have to downshift.

So for a gentle hill, if you slow down uphill, to increase your mpg from 5 to 6 mpg, and then speed up downhill, your downhill mpg drops from infinite(zero fuel used, showed as 99 on our guages) to let's say 20 mpg.

On a 10 mile long hill (5 miles up/5 down) you burn one gallon going up at 5 mpg, and zero down. Slowing down to get 6 mpg uphill, you burn 0. 83 gal uphill, and then at 20 mpg you burn 0. 25 gal down hill, so you actually burn more. This was just an example, but I remember a physics/engineering problem that asked "if you cruise for half an hour at 50 mph, and half an hour at 60 mph, and someone cruises for one hour at 55, which one gets the better mileage? (you both arrive there at the same time, since your average speed is 55 in both cases)

The guy going 55 steady gets the better mileage, due to the much higher fuel wasted when you go 60, which more than wastes the savings you got going 50. OF course this ignores engine efficiency, but for trailer towing, the speed has a much bigger influence on mpg than a little higher pumping loss in the engine at higher RPM.

That is NOT true empty, or cruising in a sports car. Most sports cars (corvettes, vipers, mustangs, not wheezer honda or tiny turbo engines), get their best mpg at 70-80 mpg, due to big displacement engines (which need a load on them to start getting efficient), tall gears (low rpm) and slick aerodynamics. Most trucks/suv's get best mileage at 45-50, and regular sedans 55-60. Trailer towing, I would guess at about 45 would be your sweet spot, but time is money too.

 

[TFlewitt]

What you say is true, but that is not how I use the data. I use it to find the most efficient speed for the load I'm presently pulling on a level road. The instant function has been very useful for this purpose. I'll have to take a look at the 2 years of chips to see if they are the same or not.

I have driven a borrowed car with instant mpg way back in the 80's, when they first came out, and I own one now with instant mpg. The instant mpg just follows your right foot. The only difference with the average guage is that you need to reset maybe 10 times, to find your sweet spot.



Now some people are obsessed with the mpg guage, and slow down uphill, for fear of seeing really low numbers (like you don't see 0 mpg at all stoplights-- is 5 mpg any worse than 0?), and speed up downhill, because the gauge "allows" them to speed with no apparent mpg penalty. That is not true. The average mpg is best if you don't speed downhill, as long as you don't use your brakes, and if you don't slow down uphill, as long as you do not have to downshift.

So for a gentle hill, if you slow down uphill, to increase your mpg from 5 to 6 mpg, and then speed up downhill, your downhill mpg drops from infinite(zero fuel used, showed as 99 on our guages) to let's say 20 mpg.

On a 10 mile long hill (5 miles up/5 down) you burn one gallon going up at 5 mpg, and zero down. Slowing down to get 6 mpg uphill, you burn 0. 83 gal uphill, and then at 20 mpg you burn 0. 25 gal down hill, so you actually burn more. This was just an example, but I remember a physics/engineering problem that asked "if you cruise for half an hour at 50 mph, and half an hour at 60 mph, and someone cruises for one hour at 55, which one gets the better mileage? (you both arrive there at the same time, since your average speed is 55 in both cases)

The guy going 55 steady gets the better mileage, due to the much higher fuel wasted when you go 60, which more than wastes the savings you got going 50. OF course this ignores engine efficiency, but for trailer towing, the speed has a much bigger influence on mpg than a little higher pumping loss in the engine at higher RPM.

That is NOT true empty, or cruising in a sports car. Most sports cars (corvettes, vipers, mustangs, not wheezer honda or tiny turbo engines), get their best mpg at 70-80 mpg, due to big displacement engines (which need a load on them to start getting efficient), tall gears (low rpm) and slick aerodynamics. Most trucks/suv's get best mileage at 45-50, and regular sedans 55-60. Trailer towing, I would guess at about 45 would be your sweet spot, but time is money too.