Quote:
Originally Posted by wmjinman
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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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.