The Craftsman 6.5 lawnmower is self-propelled, with the option to push using your own strength. With its mulching and bagging capability, this Craftsman mower uses a gas-powered engine that requires constant lubrication. To keep that engine in shape, you must choose the right type of oil and oil weight.
The Craftsman 6.50 rear deck mower uses a Briggs and Stratton engine, which is configured to accept conventional engine oil. Conventional engine oil is petroleum-based and often used in car engines as well. Conventional oil is relatively inexpensive, with the primary functions of lubricating engine parts, transferring heat away from them and keeping parts clean. The general drawback to using conventional oil is that it's inherently toxic, so you must dispose of it according to your local government's environmental standards. Low-quality conventional oil also emits pollutants via your Craftsman's exhaust system.
Synthetic oil is also acceptable for your Craftsman mower engine. Synthetic oil can cost three times as much as conventional oil. However, it lasts longer than conventional oil because it doesn't burn up as quickly in high temperatures. You can also leave synthetic oil in your mower while it's being stored because there aren't as many deposits and sediments as with conventional oil. One drawback of synthetic oil is that it doesn't lubricate new or rebuilt engine parts as well as conventional oil.
Whether you use synthetic or conventional oil in your Craftsman mower, you must consider the oil's viscosity rating. Viscosity measures the speed of the oil's distribution at extreme temperatures. Colder engines require lower viscosity ratings for optimum startup, so engine parts spend less time wearing on each other without oil. Low-viscosity oils, by nature, are thinner for that reason. Operation in warmer temperatures benefits most from high-viscosity oils because they can withstand the heat without burning out.
Consider in which temperatures you will operate your Craftsman before you choose the oil based on viscosity. If you mow only during warmer temperatures above 46 degrees Fahrenheit, it's acceptable to use SAE 30. If you operate in temperatures below 46 degrees F, use a low-weight oil such as 5W30. If you use your Craftsman year-round at temperatures between 6 and 122 degrees F, you can use a multiviscosity oil rated at 10W30.