Question: The fuel economy has dropped on my 1993 Dodge Ram pickup. I checked it recently on a trip and it was about 20 % lower than when I first got the truck. The mileage is also lower than the identical truck my brother has. I recently had a tune up done on the truck so I was expecting the mileage should be back to original. How can I improve my mileage?
Answer: Testing fuel mileage accurately is difficult using only one or two fuel fill ups. Gas tanks have an air pocket designed into the top of the tank to allow for expansion of the fuel when the tank is full. Depending upon how the truck was sitting when you filled it up, you can vary the amount of fuel enough to significantly alter fuel mileage calculations. Check the mileage averaged over several fill ups to get a more accurate calculation.
Factors such as outside temperature, wind strength and its direction, road condition, traffic volumes, and the way you drive can greatly affect fuel economy. A few quick accelerations from a stop or passing cars on the highway will quickly drop your mileage! These are reasons your fuel mileage may vary from other drivers.
There are mechanical reasons your mileage may have dropped. One common problem I see is a faulty engine thermostat. If the engine doesn't reach optimum operating temperature, the fuel injection computer delivers extra fuel because it senses a cold engine. How is your heater working? If it doesn't seem as hot, then your thermostat is likely bad. Simply replacing a bad thermostat can improve your economy.
Another mechanical problem affecting fuel economy is an exhaust leak. If there is exhaust leaking out, then air also leaks into the exhaust system. The fuel injection system oxygen sensor in the exhaust pipe detects the extra oxygen and tells the computer to deliver more fuel. Economy drops.
One of the tests a technician can do on your truck is to connect a "scan tool" diagnostic computer to your vehicle and read how the fuel injection system is working. The tool shows if the truck's computer is adding or taking away extra fuel from normal levels. The engine temperature is also accurately reported. Using this information, it is then easier to detect if something is wrong with the truck or if it is outside influences affecting economy.
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