how can you get better gas milage
A few things you could do include keeping your tires at the proper psi, eliminating any unnecessary weight, using a quality full synthetic oil, keeping the engine tuned up, and upgrading your air filter.
what is the different between full synthetic oil and castrol gtx motor oil?
GTX is a conventional(mineral based) oil. This means that it doesn't perform as well as what a synthetic would. Full synthetics cost more but can generate slightly better fuel economy, reduce engine wear, and even improve power. Just make sure it is full synthetic and not a "blended" synthetic for the best results.
Looking for a Used 300M in your area?
CarGurus has 235 nationwide 300M listings and the tools to find you a great deal.
Search Chrysler 300M Questions
Chrysler 300M Experts