Engine oil is refined crude oil. Synthetic oil is refined, distilled and purified with additives to protect engines better from wear, high heat conditions and cold weather. In areas of extreme cold or hot temperatures, synthetic oil provides better protection and better cold starts on a lawnmower. It can operate well in temperatures from 104 degrees Fahrenheit to 22 degrees below zero F. You must first remove the old oil from your lawnmower to reap the benefits from synthetic oil so the two do not mix.
Start your lawnmower and run it for about five minutes to thin the oil. Place the lawnmower on a flat surface. Pull the spark plug boot off the spark plug to prevent accidental starts.
Clean around the oil filler tube and drain plug on a riding lawnmower with a cloth. Clean around the oil reservoir on a push mower with a cloth.
Place an oil drain pan or other container underneath the oil drain plug on a riding lawnmower. Open the drain plug, remove the dipstick and allow the oil to drain until it no longer flows. Place the side of a push lawnmower on bricks to elevate the side with the spark plug. Tilt the oil reservoir on the opposite side of the spark plug towards a drain pan and let all of the oil flow out.
Turn the oil filter counterclockwise with an adjustable wrench to remove it on a riding lawnmower. Dip your finger into a bottle of synthetic oil and rub in on the seal of a new oil filter. Screw the oil filter on the lawnmower clockwise with an adjustable wrench.
Pour 10W30 synthetic oil into the oil filler tube through a funnel on a riding lawnmower or the oil reservoir on a push mower. Fill the area slowly, and then check the level on the dipstick on a riding mower or the reservoir on a push mower.
Replace the spark plug boot onto the spark plug and press it firmly in place. Crank a riding lawnmower to distribute oil into the new oil filter, and then top off the oil level to the full mark on the dipstick.