Thread: Oil temp
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Old 01-01-2013, 03:13 PM   #35 (permalink)
wmjinman
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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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