Scangauge KR

Interesting! So if a 1hp increase in engine load affects fuel economy by 1%, what happens when you go to 250 hp or 300hp? Do you loose 300% in fuel economy?

 

If what you are saying is true, you should be able to see the change as the compressor cycles on and off. Why would you not have hard numbers to back this up? You should also be able to see a change when you turn the lights on or off.

 

1hp/250 = 0.4%

But you probably don't run at 250-300hp all day long. On flat ground my truck needed roughly the following hp to maintain steady speed:

45mph: 50-60 hp
50mph: 60-75
55mph: 75-95
60mph: 90-110
65mph: 110-130

 

You can definitely see when the compressor cycles on/off. The problem is the instant mpg readout fluctuates so much anyway that you really can't tell whether it is 0.5% or 5% from watching that display, at least while driving. But you can get a much better idea at idle when using either the gph/lph or hp gauges.

The A/C compressor uses 4-5 hp when it is running. A 185amp alternator puts out 2220 Watts at 12 volts and 2590 Watts at 14 volts. That's 3-3.5hp for the entire electrical system. You're lights are a tiny, tiny fraction of that. So instead of driving for 1/2 mile or mile, you would need to drive for thousands of miles with them off and then thousands of miles with them on before having a large enough experimental sample to be statistically significant.

However, we can just calculate the energy draw by adding up the wattages:

2 headlights 19W each = 38W
14 side/clearance/marker lights 3W each = 42W
4 tail lights at 8.25W each = 33W
----------------------------
113W or 0.15hp



At 65mph/120hp the extra 0.15hp is 0.125% -- 7.30mpg instead of 7.31 so over the course of a 130,000 mile year you'd burn an extra 22 gallons (17,784 lights off, 17,806 lights on).


LED lights draw ~1/6 the energy so they would be ~19W instead of 113 (0.025hp instead of 0.15). So 7.308mpg vs 7.31 or 17,788 gal/year vs 17,784.




Side note: 113W over 2,000 hours (130,000 miles/ 65mph) = 226KWh which costs ~$80 in diesel (22gal $3.64/gal). That is 0.354 per KWh which is about 3 times what household electricity costs...

 

Again, there is no difference between the two units save the name on the unit. The D has the tools you need if you want to see your fuel cost (TFC) or your cost per mile (CPM).
Profit per mile? How can Scangauge calculate that without knowing a baseline? Every load will have a different break even point. Scangauge has no way of knowing what that is, nor is there any way to input that info. The best way to calculate your profit per mile is to use an accounting/bookkeeping program that you keep track of your expenditures and income, along with mileage.

 

Please understand this. I am not bashing Kevin Rutherford, nor the Scangauge KR. I am trying to inform people that you can get the EXACT same product for less money. Don't pay for the name is all I'm saying. You can get the Scangauge D at Camping World for $152.00 + tax. Buy the KR version and its $199.99 + tax + shipping.

 

I have a scanguge and I can't see any change as the compressor cycles on and off.

 

Bottom line, A/C is a convenience. The world has always paid for items of convenience. Personally, I would much rather pay the inconsequential amount of extra fuel per year to stay comfortable. You cannot stay comfortable without A/C. I don't know where you normally run, but where I'm from (Florida) humidity will eat you up in a heartbeat. In the summertime it gets over 95 everywhere. Again not comfortable. Running with the windows down to keep cool is not an option, especially if you're on phone calls or listening to music. You mentioned not rolling windows down. WTF??? Maybe you like to sweat and stink, but most of us would rather not, so we use our A/C for that very reason.

You claim with your numbers that it wastes fuel. We could argue that point til the end of time. We could also agree that there many other things we do that wastes fuel. For example: Why fill up your tanks and haul the extra weight? That burns more fuel. Why have a sleeper cab that weighs more when you could sleep elsewhere? Why have a spouse or kids ride with you. Why not lose 20 lbs of body weight? That's extra weight. Why plug a TV, phone charger, turn on the blower fan since they all use wattage to some degree and increase fuel consumption.Why, why, why? Anyone could nitpick anything. The thing is that all these are insignificant amounts.

 

You enter fuel cost per gallon & rate per mile into the scangaugeKR -- it will display profit per mile and profit per hour. You can use them to determine optimal cruising speed, how fast to climb hills, etc.

Neat, but more useful for those with $1.30/mile revenues.

I wouldn't own a truck without A/C. But there are plenty of times where it is 70 & dry outside and the vent is all I need/want yet I would unknowingly have the A/C on (especially with thdefroster set to low). That to me is a waste.

If the benefits are worth the costs, by all means use the luxuries that matter to you. But there is no such thing as free energy.

I'm a little surprised it costs $80/year to have "lights on for safety." But you can pretty easily find 10 little things just like it and that's $800 -- not so inconsequential to me.

While idling turn off A/C. Set the scangauge to display power & fuel useage (preferably in liters per hour). Reset trip A, time for 60 seconds, then look at gallons/liters burned. Then turn on A/C, reset trip A, & time for 60 seconds & compare.

 

The only time I turn the AC off is when climbing a long grade. I don't do it specifically to save fuel. I turn it off so the cooling system can do it's job better without the extra heat from the AC condenser.