Gas mileage has become poor

My granddaughter’s 2001 Toyota Sienna now has poor gas mileage. She will be taking it to her local Toyota dealer in Mankato, Minnesota; however, I have concerns on dollars, etc… She has poor understanding of the workings of cars. Any suggestions to correct the situation?

There are two things that can cause a sudden loss of fuel mileage.

One is the thermostat is stuck open. If the thermostat is stuck open the coolant doesn’t reach full operating temperature. The computer then thinks the engine is still cold and it uses more fuel.

The other is the coolant temperature sensor for the computer is defective. If this sensor has failed where it tells the computer that the coolant temperature never gets up to operating temperature when it actually does, the engine will use more fuel.


The most frequent causes of poor gas mileage are:
Lax maintenance
Driver behavior
Carrying too much unnecessary weight in the vehicle
The need for repair/replacement of certain parts

So, you have to ask yourself…

…Is it possible that your granddaughter, who has “poor understanding of the workings of cars” has neglected vital maintenance, such as spark plug & air filter replacement?

…Is it possible that her tires are rarely checked for proper inflation?

…Is she in the habit of idling the engine in order to warm-up the engine? In modern fuel-injected vehicles, this is not necessary.

…Does she go to drive-up windows at banks and fast food joints?

…Is she still carrying around sacks of sand that were intended for winter traction?

…Is she carrying around extra tires (other than the spare)?

And, then we come to one of the more common causes of poor gas mileage with older vehicles, namely, the need to replace the cooling system thermostat. If the thermostat is stuck in the open position, the engine will likely take a very long time to reach full operating temperature, and will use more gas as a result. With a 12 year old vehicle, the thermostat should be considered to be highly suspect.