Q I have a 2000 Dodge Durango and, for the last couple of years, when the weather turns cold my gas mileage goes down. During the spring, summer and fall I average around 15 miles per gallon, but in cold weather it drops to an average of 10 or 11 mpg. Do you have any idea why this happens? Any suggestions how to correct this?
A Perfect timing for this question, don't you think? Every motor vehicle will experience a drop in fuel economy in cold weather. One key reason is that cars take longer to warm up to operating temperature, which means the engine management system will command richer fuel/air mixtures for a longer period of time. Until the coolant and catalytic converter are up to temperature, the engine cannot deliver its best economy. Add to this our personal warm-up time -- using an auto-start system to warm the vehicle or letting the engine warm up for several minutes before driving away -- plus the slower stop-and-go traffic in metro areas, and you've got a measurable drop in mileage.
Several smaller factors also reduce mileage in cold weather: higher initial rolling resistance from cold or underinflated tires, increased mechanical drag from cold lubricants, and higher use of energy-using accessories such as the heater/defroster, rear window defroster and headlights.
Together, these easily can cause a significant drop in fuel economy during winter. How much? That's hard to predict precisely because our vehicles and driving patterns vary so much. In my experience, a 10 percent drop in mileage is about average, but it can vary widely.
Why does your mileage drop about 25 percent in cold weather? It might be worth checking to make sure the thermostat is operating properly and bringing the vehicle up to full temperature -- and keeping it there -- as quickly as possible. With many vehicles, the engine management system won't allow overdrive to engage until the vehicle is warmed up, which would further affect fuel economy.
Also, because modern vehicles really don't need much of a warm-up before driving -- and actually get up to temperature and out of the warm- up mode more quickly -- simply start the engine, let it idle for a few seconds, engage the transmission, let it idle in gear for a few more seconds, then drive the vehicle gently up to temperature.
Sure, when temperatures drop well below zero, a longer warm-up period might be useful and a bit more comfortable. It won't hurt anything but the fuel mileage.
Q The right front headlight assembly on my 2003 Lexus ES300 has developed condensation inside the front lens. The dealer says it's probably because of a broken seal that allowed moisture to collect inside. A replacement part is extremely expensive, costing $1,000 or more. Is there a lower-cost alternative such as someone who can disassemble, clean and reseal the headlight?
