Today's fuel injection solves the old problem of gas mixing with oil.

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Dear Car Talk: When I was a young lad learning to drive in Pennsylvania in the winter, I was always told that the best way to warm up a car on a cold morning was to start it, then drive away immediately but gently. It was common wisdom that to let it idle was to decrease the life of the engine, since nothing warmed up quickly enough: The moisture in the exhaust would condense more and rust the muffler; the oil would be sluggish, and thus the lubrication incomplete in the engine. Now we have cars with remote starters, and we are encouraged to start the car as we sit sipping our morning coffee in our jammies, so that the car is a tropical paradise when we finally start out on those cold winter mornings. What has changed? Are cars really designed for that abuse? Is it another case of planned obsolescence? Or is it a case of our laziness winning out over good car sense? — Richard

A: Historically, laziness always prevails, Richard. But these days, it’s not doing much harm to the car.

In the old days, when you started a cold car, the carburetor would pour gasoline into the cylinders almost indiscriminately — as if you were pouring it from a boot. Then unburned gasoline not only would come out the tailpipe and cause smog, but it also would find its way past the piston rings and mix with your oil. That meant your engine was being lubricated with gasoline and oil, instead of just oil — and gas is not nearly as good a lubricant.

But these days, all cars are fuel-injected, so the fuel is very carefully metered.  So, do you harm your car by warming it up in the driveway for 20 minutes nowadays? Not really. The biggest issue, really, is that you’re wasting fuel and creating more pollution.

But the pull of an 80-degree car interior on an 8-degree morning often is powerful enough to outweigh the 30 cents’ worth of gas you waste, and the ten-thousandth-inch sea rise you’re personally causing.

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