Many drivers think that letting their vehicle warm up for fifteen or twenty minutes on a cold morning is the right thing to do.  Yet, it is actually improper to let it sit and gently warm up, and it wastes gas.  Most cars today use electronic fuel injection. When your car’s engine is cold, the computer tells the fuel injectors to stay open longer, allowing more fuel into the engine to help it run cold. As the engine warms up, the injectors let in less fuel and everything returns to normal function. However, letting the car idle is the absolute slowest way to bring it up to operating temperature. A further problem is with the catalytic converter.  This is a device in the exhaust system that works to burn off unburned hydrocarbons in the exhaust stream. A cold engine emits a far higher percentage of unburned hydrocarbons than a warm engine and most catalytic converters can’t process 100 percent of unburned hydrocarbons even in the best of times.  The catalytic converter needs high exhaust temperatures to work properly. If you have a cold engine emitting a high percentage of unburned hydrocarbons, over the course of many cold days, you can end up with a “plugged” converter: the converter becomes overwhelmed and literally ceases to function. This will take a long period of time to happen, but the end result of letting your car warm up on a daily basis will only lead poorer mileage and significantly dirtier exhaust.

So, what to do? Even when it is very cold out, let the vehicle run for 30 to 60 seconds to get all the fluids moving, then drive off gently. The engine will warm up faster, the exhaust system will get up to temperature faster, the catalytic converter will work more efficiently, and you will use less fuel.