I work for a university where students are often approved for a Sallie Mae loan, but usually only for a small amount (less than $2,000). When the amount gets higher, then factors like income and the length of your credit history will matter more.
Getting Started. Fouled, damaged, or worn out spark plugs can lead to a variety of engine problems, such as misfires, hard starts, increased emissions, and poor fuel economy. For most vehicles, you should replace your spark plugs every 30,000 miles (consult your owner's manual for your specific interval). It is also recommended that you replace your spark plugs wires at the same time, or you may still experience misfires or other problems.
High performance engines and engines that rev to high RPMs also tend to wear out quicker. For all of these reasons, it's important to replace your spark plugs from time to time. Fortunately, high-quality spark plugs should last tens of thousands of miles, so replacing them is not something you'll have to do often.