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Old 12-27-2012, 09:33 PM   #31 (permalink)
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I run 5W20 in the Ranger and the Fiesta. I never let the engine run without getting moving. I will pulse and coast (engine on), even in the first .3 mile out of my neighborhood.
After sitting a week my 1937 Ford flathead coupe would produce 60 PSI of oil pressure in 5 seconds of cranking (it had a starter button for ignition off). Thats a direct drive 6 volt starter cranking at 100 RPM, less than 10 revolutions of the engine.
The cranking speed of most modern cars is about 300 RPM. which means you get the same pressure in 1/3rd the time, or less than 2 seconds.

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Old 12-30-2012, 03:05 AM   #32 (permalink)
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Quote:
Originally Posted by rbrowning View Post
I guess the question I would like to see a definitive answer to is:

Is the fuel consumed in running an engine at idle for a minute more than offset by the reduction in fuel consumed because of the warmer oil?

Yes, obviously the fuel consumed is "wasted" because it doesn't move you down the road, like the example of the winglets on the airliners. They add drag, they produce no lift therefore they are bad, right? Wrong, they improve the lift by keeping the airflow over / under the wing without it slipping off the end of the wing. Can the fuel burnt by idling the engine a minute improve the efficiency when the engine is under load enough to pay for itself?
It shouldn't be too hard to test. Either with a ScanGauge or without. Start up the car & take off without warming it up & drive it for 5-10 minutes or so on a given route, come home & park. Next morning, repeat. Next morning, repeat again. Etc. Check mileage. Then do it again, but let "warm up" for 1 minute (60 seconds on the stopwatch) each time before taking off. Check mileage. And there will be the answer - It'll either help, hurt, or have "inconclusive results"?

With a ScanGauge, just do a "trip" average "current-reset" each time & note it. Then you can even spend the rest of the day driving "normally". But check it each time you do a cold start in the "morning".

Without a ScanGauge, there would probably have to be about 10 cold starts & drives on 10 different days for each the "no warm-up" and "with warm-up" tests checking mileage at the gas station when filling up. Obviously, it would be very important to drive the exact same number of identical trips for each the "warm-up" and "no warm-up" halves of the test and to fill up to the exact same level both times - same station, same pump, same time of day, etc, etc,
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Old 01-01-2013, 03:35 AM   #33 (permalink)
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earlier today I started the truck and it idled cold at around 1300 rpm, when i switched on the fan to full it dropped at least 100 rpm, so a bit of load there, could that change the mileage a bit to run with only normal draft air and no fan, should be about 1/10 HP difference if the fans on high . some one else posted something about this somewhere. and Happy new year Guys and Girls . May all your trips be downhill and downwind.
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Old 01-01-2013, 04:16 AM   #34 (permalink)
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Quote:
Originally Posted by wmjinman View Post
It shouldn't be too hard to test. Either with a ScanGauge or without. Start up the car & take off without warming it up & drive it for 5-10 minutes or so on a given route, come home & park. Next morning, repeat. Next morning, repeat again. Etc. Check mileage. Then do it again, but let "warm up" for 1 minute (60 seconds on the stopwatch) each time before taking off. Check mileage. And there will be the answer - It'll either help, hurt, or have "inconclusive results"?

With a ScanGauge, just do a "trip" average "current-reset" each time & note it. Then you can even spend the rest of the day driving "normally". But check it each time you do a cold start in the "morning".

Without a ScanGauge, there would probably have to be about 10 cold starts & drives on 10 different days for each the "no warm-up" and "with warm-up" tests checking mileage at the gas station when filling up. Obviously, it would be very important to drive the exact same number of identical trips for each the "warm-up" and "no warm-up" halves of the test and to fill up to the exact same level both times - same station, same pump, same time of day, etc, etc,
I'm pretty sure idling to heat the oil is going to burn more fuel, because most of the heat energy of the engine goes out the tailpipe, not the coolant and oil. When you idle to heat the engine, you transfer maybe 20-30% of the fuel's heat energy into the engine. When you drive the car, you get that, the extra losses from pumping the cold oil (converting some of the 25-35% of the net mechanical work into heat via friction, dumping it directly into the oil), and you use the engine to do useful work at the same time. You get more efficient heating of the oil when the engine is cold this way, that is you have more fuel energy going into heating the oil, which is energy that you cannot get out of investing every time the car is driven.

I've started to switch the engine off at stoplights when it's cold.

Last edited by serialk11r; 01-01-2013 at 04:28 AM..
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Old 01-01-2013, 04:13 PM   #35 (permalink)
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Quote:
Originally Posted by serialk11r View Post
I'm pretty sure idling to heat the oil is going to burn more fuel, because most of the heat energy of the engine goes out the tailpipe, not the coolant and oil. When you idle to heat the engine, you transfer maybe 20-30% of the fuel's heat energy into the engine. When you drive the car, you get that, the extra losses from pumping the cold oil (converting some of the 25-35% of the net mechanical work into heat via friction, dumping it directly into the oil), and you use the engine to do useful work at the same time. You get more efficient heating of the oil when the engine is cold this way, that is you have more fuel energy going into heating the oil, which is energy that you cannot get out of investing every time the car is driven.

I've started to switch the engine off at stoplights when it's cold.
I understand - and I don't disagree. But rbrowning was saying he'd like to see definitive proof one way or the other. The intent of my reply was just to say, "It shouldn't be that hard to get definitive proof", and if I were to do the test, this is how I'd do it. - - - and I might - just for fun. I've got a ScanGauge, so doing a few "drive off immediately" cold starts (like I normally do), taking the same route out of the nieghborhood, and logging the mpg for the first 5 or 10 minutes of the trip vs doing the "one minute warmup" first, and THEN driving out of the neighborhood taking that same route shouldn't interfere with my daily life too much.

And then, hopefully, the results don't fall into the "inconclusive" region, and I can post my "definitive results" for everyone of "ooh" and "ahh" over.

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