While synthetic oil is a good option and offers some advantages, conventional 5W-30 is perfectly suitable for a car with that mileage. Using a higher viscosity oil (like 10W-30 or 20W-40) is generally *not* recommended unless specified by the owner's manual for hotter climates or more strenuous use. Always check your owner's manual for the manufacturer's specific recommendation, as it will give you the best guidance.