A dirty air filter will NOT affect fuel mileage and replacing an air filter will NOT increase fuel mileage. Air filters do get dirty and should be replaced when they are dirty, but fuel mileage will not be affected. Restricting air flow is much like releasing the throttle on the vehicle. As less air enters the engine, less fuel is added. Performance may drop, but mileage will not.
2. Small cracks in a serpentine belt means the belt is bad
Small cracks in the ribs of a serpentine belt are fairly common and do not necessarily mean the belt is bad. Many high quality original equipment belts are replaced with aftermarket belts that are not as good as the belt replaced. Fraying of the belt, exposure of the cord, deep cracks to the cords missing pieces and wear in the teeth area mean a serpentine belt is bad. Ironically, modern EPDM belts may show no cracks at all yet can be can be worn out. A special gauge made for the purpose is the best way to check a serpentine belt for wear.
3. Fuel injectors should be routinely cleaned
Fuel injectors are self cleaning and rarely need attention unless contamination enters the system. Dirty injectors will normally show up as a rough idle. Routine injector cleaning will not increase mileage, extend engine life and may be bad for the fuel system. The best way to prevent injector problems is by using high quality fuel.
4. Rotate and balance
Tire rotation is maintenance and helps to even out tire wear. Wheels are balanced when the tires are installed and a proper balance will last the life of the tire. Rotating tires will NOT affect balance. If the tire is taken off of the wheel or if a balance weight comes off of the wheel, balance is needed. The symptom of improper wheel balance is vibration or steering wheel shimmy while driving 30 MPH and faster.
5. Wheel alignment every year
Wheel alignment is not maintenance and does not need to be routinely performed. Vehicles are not knocked out of alignment by hitting potholes, unless something is bent or damaged. The symptoms of wheel alignment include tire wear particularly to one side or the other, a crooked steering wheel when driving straight and/or a pull to the right are left that is constant at all speeds.
6. Synthetic oil last longer than conventional oil
Synthetic oil can tolerate far more abuse than conventional oil and offers better protection to the engine. It also cleans better than conventional oil and will get contaminated just as fast. Driving style determines the need for oil change, not mileage and not the type oil used. Short trips, under five miles mean more frequent oil changes. If the vast majority of driving is for longer periods, ten miles or more, oil changes are needed less frequently, with or without synthetic oil.
7. Nitrogen in tires will extend life and increase mileage
This is totally false as proper inflation with air (80% nitrogen) offers the same benefit as proper inflation with nitrogen or any other gas. Improperly inflated tires wear and decrease mileage regardless of their content. Exact inflation is not a precise science. For guidelines see our Detailed Topic on tire inflation.
8. Leakage means shocks and struts should be replaced
Minor dampness around the shaft of a shock or strut is fairly common and does NOT signal a problem. Oil covering the shock or strut housing or dripping off the housing signals a need for replacement. Shocks and struts are often replaced with units that are of lower quality than the part replaced. Some of the symptoms of bad shocks or struts include excessive bouncing when driving, noise on bumps and excessively rough ride.
9. Fuel and oil additives are good for a vehicle
Name brand fuel from a high volume station contains everything an engine needs. Additives like fuel injector cleaner are NOT good for the vehicle and can sometimes cause problems. The proper viscosity engine oil, replaced on a regular basis will not benefit from oil additives. Engine oil additives can cause adverse effects and should not be added.
10. Tire dressing is good for tires
Tires do NOT require any type of dressing. Quality tire rubber contains an anti-ozone material to protect the tire. Some chemicals used as tire dressing can contribute to side wall cracking and damage the tire. Excess tire dressing can also get onto brakes and cause problems. Simply washing tires with soap and water when they are dirty is all that is needed.
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