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GasSavers_maximilian 08-18-2009 05:05 PM

Accurate way to measure idling fuel consumption
Because the amounts are so small, I want to be sure and measure the fuel consumption of my car while idling accurately. How much of a run do you guys think I need on my SG2 to be accurate? Any tips on testing procedure would be useful too. Thanks!

FrugalFloyd 08-18-2009 06:54 PM

You only need to run your car until it's warmed up to get a baseline idle fuel consumption. Five minutes is probably enough, but you can go to ten to be sure the car is warmed up. My Nissan drinks .22 gph, but my Scion only drinks .15-.17 gph. When they're cold, .35-.5 gph isn't unusual.

If I'm getting 60 mpg at 30 mph avg, I'd use a total of .5 gallon to go 30 miles in an hour. In a typical low speed scenario like that, I'm pulsing 1/3 of the time, and FASing the other 2/3. But if I were to coast NICE-on, I'd add another .2 gallons X 2/3 hour, or .133 gallons to my fuel consumption. That would bring my 60 mpg down to 30 miles/.633 gal, or 47.4 mpg. That's a significant cut in mileage, and is one of the reasons my wife's AT car only gets 40 mpg on the same country road route that I can get 60 mpg on with either of my MT autos.

GasSavers_maximilian 08-19-2009 04:23 AM

My initial estimate is around .19 gph, but I'm not sure how accurate that is (pulled it from my coast down data). I'll rerun things the next time I'm out and the engine is warmed up anyway. Probably not critical for my P&G calcs anyway, but it'd be good to know.

GasSavers_maximilian 08-19-2009 04:29 AM


Originally Posted by maximilian (Post 140072)
Probably not critical for my P&G calcs anyway, but it'd be good to know.

Wrong. For 5 mph P&G ranges it matters a lot. I'll rerun my program after I get the idle info.

GasSavers_maximilian 08-19-2009 09:19 AM

Much easier to do while not driving! I used my stopwatch to time how long my SG2 took to get to .03 gallons. Sitting there wasting fuel was hard! Took 530 seconds, so that's 0.20 gph, which is pretty good agreement with data from my coast down.

FrugalFloyd 08-20-2009 12:55 PM

You might not be aware there's a gph function on the SGII, so you didn't have to monitor current trip fuel consumption and calculate it over time.

GasSavers_maximilian 08-20-2009 01:05 PM

Yeah, I noticed that yesterday afternoon when trying to get IAT to show up. Didn't know it was in there. :o It shows either .21 or .22 when coasting. Slightly different than the idling calculations, and since they're both reliant on the SG2, I wasn't positive which to go with. I just called it .21 and ran my program.

Time for me to re-read my SG2 manual.

bowtieguy 08-20-2009 03:41 PM

a bit OT, but i found this on another thread... http://www.milesgallon.com/calculate...t_per_mile.php

i put $1 for selling price because it wouldn't take zero and i put miles on the car when i got it for miles when new. couldn't understand that one. oh, and i put 10 years for ownership.

anyway, it says i get 14 cents/mile. but it does not account for maintanence. even @ similar miles driven and similar vehicles, there must be a huge variance in cost regarding maintaining a vehicle.

GasSavers_maximilian 08-20-2009 04:57 PM

I use the Edmunds TCO numbers and then divide by the mileage to compute $ / mile. I made a spreadsheet so I can adjust their values to be more in line with my needs.

Larry1LT 10-21-2010 12:30 PM

Re: Accurate way to measure idling fuel consumption
Is it normal for my 2010 Kia forte 2.0L 4spd automatic to consume 0.3+ gph at idle when warmed up? Also, is there any way to lower the idle speed on newer cars?

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