When you purchase a car, one of the prominent issues that haunt your mind is which oil to use at the time of oil change. Having spent a lot of money on purchasing the vehicle, you really don’t want to undergo any risk by resorting to cheaper oils. At the same time, you may also be prepared to go for the `second-quality’ oil, if that doesn’t call for trouble. Nevertheless, a variety of factors determine the kind of oil required for a vehicle. Undoubtedly, fully synthetic oil is best suited for any vehicle in the long run, despite costing more, because you are actually saving the service life of your vehicle with synthetic oil. On the other hand, half synthetic oil, which is a mixture of conventional oil and synthetic oil in 75:25 ratio, provides better performance only over fully conventional oil and not fully synthetic oil. Fully synthetic oil offers a much purer base oil and is the ideal choice, particularly if you own a new car because the oil is designed with improved lubricate properties and enhanced viscosity. This provides superior protection from engine wear, reduced heat breakdown, improved fuel mileage and easier engine cold storage. Semi synthetic oils do not typically include all the advanced additives of fully synthetic oils. So they are more preferred for older vehicles due to the engine seals. Trying fully synthetic oil with older vehicles may lead to oil leak as there can be a build up of waxes and sludge left by semi sythentic oils over time which may mask worn engine seals.