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More mechanical problems
Here are some additional problems that hurt fuel economy:
More engine problems:
- high idle speed
- high fast idle speed when cold
- incorrect idle mixture adjustment (carburetor or fuel injection)
- leaking fuel line or carburetor (dangerous too)
- clogged jets (calibrated holes) inside carburetor
- defective power valve in carburetor
- worn camshaft lobes
- high alternator voltage (should be about 14 volts when warm)
- high oil level (interferes with crankshaft movement)
- high oil pressure (relief valve stuck or has wrong spring)
- stuck cooling fan clutch (runs fan when not needed)
Problems that increase rolling resistance:
- sticking disk brake calipers
- tight drum brake adjustment
- warped brake rotor or drum
- sticking parking brake cable
- incorrect wheel alignment, front or rear (check tire wear)
- worn suspension joints (ball joints, steering joints)
- worn control arm bushings (changes wheel alignment)
- worn or incorrectly adjusted wheel bearings
- leaking grease seals for wheel bearings
- use of snow tires when not needed
- leaking tires, causing loss of pressure
- warped tires
- bent rims, causing car to shake
- poor wheel balance, causing shaking at high speeds
- worn shocks or springs (forces driver to brake more)
Automatic transmission problems:
- wrong fluid level
- incorrect throttle valve cable adjustment
- bad vacuum modulator or vacuum hose to modulator
- sticking valves in valve body, causing delayed shifts; changing transmission fluid may help
- failure of torque converter to lock up (if equipped with lock-up torque converter); it should engage at 30-55 MPH, reducing engine speed about 10%
- stuck stator clutch in torque converter
Manual transmission problems:
- wrong fluid level
- excessive oil viscosity
- bad bearings
- failure to engage one or more gears
Differential problems:
- wrong fluid level
- excessive oil viscosity
- bad bearings
- high ratio ring and pinion gear set installed for racing
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