The type specified by the vehicle manufacturer in your owner's manual. For most passenger car and light truck gasoline engines today, it's any oil that meets the American Petroleum Institutes "SH" rating. As for the viscosity of oil to use, most new engines today require a multiviscosity 5W-30 oil for all-round driving. The lighter 5W-30 oils contain friction reducing additives that help improve fuel economy, and also allow the oil to quickly reach critical upper valvetrain components when a cold engine is first started. Most engine wear occurs immediately after a cold start, so it's important to have oil that is thin enough to circulate easily -- especially at cold temperatures.

Because the internal combustion engine is an inherently dirty design. But with the right controls and add-on devices, it can run exceptionally clean -- not as clean as a zero emissions vehicle like an electric car, but clean enough so as not to pose a serious threat to the environment.

The catalytic converter is our main line of defense against air pollution, so it's important to make sure it is functioning efficiently and passing exhaust without creating undue restrictions that might reduce performance, fuel economy or emissions. That's one of the reasons for periodic vehicle emissions testing. If the converter isn't working, you won't pass the test.

Not unless you are willing to risk electrical damage or a fire! A fuse is a protection device that is designed to blow if the amp load in a circuit exceeds the "safe" limit for that circuit. Fuses are built with a specific amp rating which is marked on the fuse. The wiring and design load of the circuit dictates the size of fuse that's required to protect the circuit. Circuits that draw a lot of power need fuses with high amp ratings (20 or 30 amps) while those that use minimal power require smaller fuses (5 to 15 amps).