Edmunds Answers



  • zaken1 01/20/12 12:09 pm PST

    This is not only usual; in fact it is COMMON with all types of cars during the winter months. In your case; it is caused by three factors: One is that new motors will not get good fuel economy or perform at their potential until after they have run far enough to wear down the microscopic high spots on the cylinder walls and piston rings, and develop a close fit between those parts. This "bedding in" process is essential to a well running motor; and usually takes over 2,000 miles to achieve. As the motor breaks in; the compression gradually increases, the internal friction becomes less, and it develops greater and greater performance and fuel economy.

    The second factor is that all internal combustion motors generate excess heat; which is regulated by releasing it into the atmosphere through the radiator. There is a thermostat in the engine which regulates the flow of coolant through the radiator; in order to keep the coolant and intake manifold at a temperature that is hot enough to vaporize the fuel which is constantly being injected into the engine. But when the ambient air temperature drops below about 50 degrees F; the amount of heat drawn out of the radiator by the cold air becomes enough to require the engine to burn excess fuel just to maintain the desired coolant temperature. Your home heating bills rise drastically in the winter; and so do your cars fuel costs, for the same reason.

    The third factor in this conspiracy is that fuel refiners are required by law to add oxygenating chemicals to the fuel they produce dirung the winter months. These oxygenates (typically ethanol and related compounds) reduce carbon monoxide pollution during cold running; but they also reduce fuel economy.

    If you wait until after the motor is broken in, and the warm months arrive, and then check your mileage again; you'll get a realistic measure of the car's true fuel consumption.

    I also would like to point out that it is possible to be too easy on an engine during break in; and thus not put enough pressure on the piston rings to allow them to properly seat in. It is recommend to (only after the motor has reached normal operating temperature) do a series of acceleration runs from about 35 mph to about 55 or 60 mph at half to 2/3 throttle; progressively increasing the thrttle opening during the process.. These runs will enable the rings to seat properly; and will pay off in improved performance throughout the life of the motor. About ten of these runs spaced out over a few hundred miles is what it takes. You should be able to feel the engine becoming stronger and more responsive as the break in process proceeds.


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