2004 lancer what kind of oil 10w-30 full synthetic or regular oil

Cris, you are not telling us how many mile your engine has on it. So, the way I look at it, this is a depends question. The problem that most people encounter when switching a high mileage car to synthetics is due to the detergents in the synthetic oil. The conventional oil sludge accumulates around the gaskets and other places, often times preventing leaks. The synthetic oil begins to remove this sludge and things like oil pan gaskets, main seals, and valve cover gaskets beging oozing oil. If you do a regular oil change, check your oil level, there is really no reason why you should not continue to use regular motor oil.