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Why Does My Car Lose Gas Mileage?

By Junior Damato, February 23rd, 2019

strong>Dear Doctor: I'm the original owner of a 2009 Toyota Matrix with 66,000 miles. Since new it has been consistently getting 30 mpg no matter where I drive, but about nine months ago fuel economy slowly began to drop. The mpg went from 30 to 28, then 26, then 24 and now it is 22 mpg. During the winter, the car is kept garaged. My local mechanic said I should take it to Toyota to have the codes scanned. He said it can be costly to repair. What may be the cause in fuel drop? Irvin

Manufacturer photo: 2009 Toyota Matrix
Manufacturer photo: 2009 Toyota Matrix

strong>Dear Irvin: There are a number of reasons for a loss of fuel mileage and all can be checked by an ASE Master Technician for proper diagnosis. The first step is a full-engine scan test with a professional scan tool. This would include all systems. Sensors can sometimes be lazy to operate at factory specs without setting a check engine light. The engine must get up to operating temperature before the computer goes into what is called "closed loop." The computer then looks at all of the input information oxygen sensors -- also called air ratio sensors -- which do wear and become slow to operate. Dirty fuel injectors, partly blocked air intake systems are also part of the fuel management system to be looked at.

strong>Dear Doctor: We love our 2009 Nissan Altima coupe. Occasionally when starting the car we hear a noise that sounds like it's coming from beneath the steering column or near the center of the dash. The noise sounds like a vibration, almost like a duck quacking, and sometimes like something is inflating or deflating rapidly. It lasts for only a few seconds and then goes away. It does not appear to affect the starting or running of the car, it's just more of an annoyance. What is causing this noise? Jim

strong>Dear Jim: The noise you describe sounds like a blend door actuator inside the plastic heater box. There are at least three blend door actuators that control the temperature and the position that the air blows out of the system. You need to have a qualified technician listen to and diagnose the sound.

strong>Dear Doctor: I have a 2007 Honda CR-V. Its windshield wipers and rear wiper want to creep up on the windows rather than stay set in place. I have to turn the wiper switch on then off to get them to go into their original setting. What should I do to correct the issue? Alan

strong>Dear Alan: I have seen many Honda vehicles with wiper problems like this, and 90 percent of the time the fault is the wiper motor. For some repairs the replacement of the wiper motor cover will resolve the problem. The other choice is to replace the motor to the wiper. You can also ask your technician about a used motor replacement.

strong>Dear Doctor: I read your advice to a reader that premium gasoline burns hotter than regular or mid-grade. Hot or high-octane gasoline does not have any higher energy content than regular gas. In my small engine equipment (chain saws, 4-wheelers, etc.) I burn 100LL aviation fuel to guard against the negative effects of ethanol in today's filling stations. Shell Oil, Chevron, and Phillips fuel specs indicate an actual lower heat content (BTU/lb) for aviation fuel than auto gas. What do you think? Joe

strong>Dear Joe: I cannot comment on the results of the oil companies' fuel specifications, but the higher the fuel octane, the slower and hotter the combustion. In cold weather, some engines will be harder to start and could hesitate until the engine is warm. I use aviation fuel in the summer on outdoor power tools and performance boat engines. I have never had an engine burn out from the use of aviation fuel. In the old days of carburetor engines and engine run-on pre-ignition, the use of premium gasoline would eliminate the problem. That indicates the higher temperature needed to light off the fuel.

strong>Dear Doctor: I have a 2019 GMC Yukon XL Denali 4WD with the 6.2-liter engine, 10-speed transmission, and 22-inch wheels. I feel every bump in the road. When I test-drove the 5.3-liter six-speed with 20-inch wheels, the ride was much smoother. Can I replace the 22-inch wheels on my Denali for 20 inchers? If not, what would you recommend to make my SUV drive smoother? Richard

strong>Dear Richard: Yes, the switch to a 20-inch wheel and tire size will make the ride much smoother.

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