The viscosity of boat motor oil is one of its most important properties, as it measures how any given oil will flow. Thicker oils will generally have a higher viscosity than thinner oils. The viscosity of boat motor oil is essential for productive engine operation.
The numbers and letters on boat motor oil packaging refer to measurements that have been taken at specific temperatures. A “W” means the oil meets viscosity specifications for winter use. Multi-viscosity boat motor oils prevent the oil from thinning as it warms up because polymers have been added to prevent the oil from thinning. It is wise to use multi-viscosity boat motor oil with the narrowest span of viscosity for the temperatures you will encounter-in the winter, for the lowest expected temperature, and for the summer, for the highest temperature anticipated.