First off, my credentials to make following statements: automotive engineer, 30 yrs experience. Worked as an engineer for Mitsubishi, Mazda, BMW & Porsche, plus as a field engineer (investigative) for one of the Big 3 for about 8 years. Doesn't mean I know everything, but I actually had some input on this issue with one of the manufacturers and talked to my counterparts at other companies regarding this.
The biggest concern manufacturers have in idling is simply that it worsens their corporate fuel economy number. As in, makes it worse, and the government doesn't like that.
We had a lot of cars in port storage a few years back and their batts were going flat at about 1 - 1.5V /mo. We checked with the manuf. about fuel consumption when idling so we'd have enough fuel in the tanks that they wouldn't all go dead out there. (We were idling them to recharge the batts) I don't remember the numbers now but it was very small, perhaps about 0.3 liters of gasoline/hr? No also not a big individual contributor to pollution but if everyone's doing it, it becomes a mass issue.
Modern engine assembly tolerances and metallurgy are significantly better managed during all aspects of manufacturing so that during warm-up the various interacting metals, often specially coated or alloyed to reduce wear, don't need as much time or heat energy to come to tolerance. But, IMHO, we also knew that the average driver would often hot-foot it outa the driveway on a cold day in Michigan oblivious to the simple laws of physics, metallurgy and wear. Not good.
The best thing in the cooler months, unless it's very cold like it is here now in central WA St. (-3˚ this morning), is to start it, let it idle for perhaps 30 - 45 seconds, and then proceed out at normal driving speeds without WOT (wide open throttle) operations for 3 - 5 minutes. If it is fairly cold (i.e. < 25˚ F), you should let it idle for about 2 minutes. Gets the coolant circulating, the oil everywhere in the engine, and some temp energy migrating into manifolds, etc.
If it's quite cold (< 15˚ F) then please let it warm up for about 5 - 10 minutes out in the driveway. Note that this does nothing for the auto trans until you start moving and circulating that trans fluid up through it's intercooler next to or under the radiator . You will likely notice the auto trans is a bit sluggish, but don't try to tell it who's boss by going WOT and forcing it to do things your way. Fast way to buy yourself a trans job (about $3500 if done right...).
If you are only driving a short distance and then shutting off, good luck to your engine! That's the worst thing to put them through. You can have a "Winter Front", a radiator blind or wbig block 7.3 turbodiesel International Harvester engine is so cold-blooded that it won't warm up for at least 15 - 20 minute, and that's only if it's "worked" a bit. It's such a big engine block that it just takes a long time to warm up. Very hard on the engine if I don't warm it up for about 15 minutes before starting out (that's if I didn't plug it in). Even then, the auto trans doesn't like to work. I simply
have to plug it in every night, but I use a high-amp capacity outlet timer to turn the block and battery heaters on at about 5:00am for 3.5h, not all night. That's unnecessarily long and energy-wasteful.
The Ford block heater system also includes heated battery blankets. I wish it had a trans fluid warmer and I may install one next summer. When it's warm! Amsoil™ also offers a pre-oiler pump system to power up the engine oil pressure before starting the engine. Now we're getting serious! And engines treated like that go for a million miles, easy! You'll get the full benefit of all those well-managed manufacturing tolerances!
Use synthetic engine and ATF fluids if approved for your motor. (Not always a good idea in older designs or very worn engines; they can really start using/burning oil if you switch). They certainly protect fabulously at high loads and temps, and they generally flow better when cold, cling to surfaces overnight for the horrible first few seconds after startup when, with well-worn, dirty regular oil, there's precious little protecting your metal to metal surfaces. You know, little inexpensive items like the crankshaft, bearing journals, camshaft lobes, etc. etc.
I knew the owner of a rare Aston Martin who installed a simple electrical system switch that allowed the engine to crank over but the ignition system to not work. He'd crank the engine to the count of about 5 seconds and flip on that ign switch. This pumped oil into the system under pressure and only
then the engine lit off. Last I heard, that motor had about 330,000 miles on it with only a head gasket at 200,000.
Treat 'em like babies, warm them up a bit in the morning, and drive gently for the first few miles, and they'll smile back at'cha! Plus you'll have some defrost and floor heat comfort!
Well, that's my two bits worth. Happy motoring!
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Warm-ups: It's Mostly a Good Thing
