What’s Wrong With My Fuel Economy?

John Paul, aka “the Car Doctor,’’ answers readers’ car-related questions.

By John Paul

May 6, 2015

3 minutes to read

Q. I am hoping that you can help me find a solution to my problem of poor gas mileage on my new 2015 Toyota Camry, purchased the end of on 2014. The sticker says the fuel economy should be 25 miles per gallon in the city and 35 miles per gallon on the highway. In the 2,200 miles I have driven so far, I average city-highway combination is about 23 mpg. My dealer checked it out and said nothing is wrong. I took it to another dealer who said the mileage ratings are under “ideal conditions’’. I bought the car on reputation, and mileage. This is the first car that has not at least met the numbers on the sticker. I got better mileage on my 10 year old six-cylinder Buick, than on this four-cylinder Camry. What should I do?

A. I think time is what is necessary to see the estimated EPA fuel economy. It has been my experience with many new cars they don’t return the projected fuel economy until the engines reaches 5-7,000 miles, some engines even more. To some extent the dealer who told you that the mileage is under ideal conditions is correct. The gasoline that we use in winter combined with winter warms and short trip can have a dramatic impact on your car’s mileage. If there is nothing physically wrong with your car, I believe the fuel mileage will improve over time.

Q. My 2007 Toyota has 115,000 miles on it. When I brought it in for transmission fluid change at 100,000 miles per the owner’s manual, the service tech at my dealership told me it wasn’t necessary. The technician told me that the transmission fluid was good forever. What do you think?

A. Toyota has two recommendations for transmission fluid changes, depending on how the car is driven. Under normal conditions, the fluid should be checked regularly and changed if it shows signs of discoloration and wear. If the car is driven more aggressively, the fluid should be changed every 36 months. If the fluid looks okay, leave it in the car. If the fluid is dark and burnt have it replaced.

Q. I have been told, and have experienced, that if a modern car is allowed to stand unused for about two weeks that the battery will drain to zero and not start the engine. The explanation given by my very competent mechanic is that the computer is programmed to let this happen. Why, if true, would any computer programmer cause this to happen? Is this some safety feature or are they in bed with battery companies?

A. We have certainly seen evidence of this over the past winter as people have left their cars for weeks at a time. Cars today have so many electronics in them that it can be a burden to the cars battery. In most cases, the electronics are designed to go into a “sleep’’ mode to minimize the chance of a discharged battery. Most cars will easily be able to sit for three weeks, and in some cases more, without the battery becoming fully discharged. In fact the car’s computer is programed not to let this happen and in many cases will shut down power robbing systems. I would have your car tested just to make sure that all the systems are shutting down as they were designed to.

Q. We have a 1996 Nissan 4X4 pickup with a small plow that we have used this past winter. We have put in new battery cables, a new alternator, and a new battery. If the headlights or heater are on while we are plowing, the truck will start sputtering and quit within 30 minutes and the battery will be dead. If the headlights and/or heater are not on, it will run a little longer, but will still eventually quit. What could be wrong?

A. The output voltage of the alternator should be checked to see exactly what is happening. At first impression, it would seem as if the alternator belt is slipping. Recently I saw a very similar problem and the belt was slipping because the crankshaft pulley was starting to separate and would spin under load and stop charging. When testing the alternator it is important to look at both voltage and amperage. The voltage output should be between 14.1 and 14.7 volts and when tested the alternator amperage output should be more than 47 amps at 2500 RPM.