What would cause bad gas mileage for a 2005 Chevy classic?

Answer 1

This question poses ALOT of potential responses.

1. The air filter could be dirty and need cleaning or replacement, only clean a cleanable filter, such as an Air Hog (r) TM or K&N, this is also a good time to upgrade to one of the cleanable filters.

2. As the seasons change there are many things that change as far as general performance. Heat i.e. hot air is less dense than cold, so your fuel is less efficient due to its volume being less dense, your gallon of gas in December is "more fuel" than in the dead of summer, additionally by the oxygen in the air being less dense it is less oxygen per volume than in the winter, this is why a deep breath in the winter feels more fulfilling than in the summer

3. The exhaust could have any number of issues, it could be an oxygen sensor, if you have a shop manual and a volt tester as well as a blow torch you can usually test this yourself by measuring voltage output or voltage resistance depending on the O2 sensor, the next issue could be a congested catalytic converter, or muffler. lastly has the piping of the exhaust suffered any dents or compressions, as the restriction of airflow out is as important as the restriction of airflow coming into the engine.

4. The spark plugs, or spark plug wires could be needing replacement or cleaning. again this is an opportune time to upgrade to a recommended performance plug that will spark hotter to allow more of the fuel in the cylinder to ignite and burn more effeciently, producing more horespower and torque, in turn reducing the ammount of rmp used to acieve optimal economy

5. the transmission needs to be regularly serviced, per the owners manual recomendations, it is well worth it to have the Transmission Fluid and filter changed or replaced regularly as recommended by the manufacturer, there is a significant loss of torque and horsepower already through the drivetrain when it is in pristene new condition, and as the fluids break down and the filter acumulates debris it becomes less efficient and needs to be given attention to reclaim the previous specification for power transfer

6. there are very simple things as well such as making sure your alignment is correct, your tire pressure is at the recommended level using either the label inside the drivers door or the pressure recommended on the sidewall of the tire, pay attention too though as it recomends the "cold pressure" i.e. when the tire is cold is when you should fill to the recommended pressure, this again goes with the density of air and the expansion due to increased atmospheric temperature. additionally if you fill your tires to xx psi in December, then in June the psi may have significantly increased, a way to combat this is to fill your tires with compressed nitrogen, as it is not effected by atmospheric temperature changes

7. the final recomendation is to make sure the oil is fresh and changed every 2750 to 4250 miles, or every 3-4 months on a regular schedule, do not re-use the oil filter unless it specifies that it is acceptable for xxxx miles. also consider using an additive in your fuel that will clean or remove carbon build up from the cylinder, cylinder head, walls, and passageways