Oil Ratings - What they mean.
10W what?

The Viscosity Rating is a measure of an oil's flow characteristics, or thickness, at certain temperatures.

The low-temperature viscosity (the first number, 5W in a 5W-30 oil) indicates how quickly engines crank in winter and how well the oil will flow to lubricate critical engine parts at low temperatures. The lower the number, the more easily the engine will start in cold weather.

The high-temperature viscosity (the second number, 30 in a 5W-30 oil) provides thickness, or body, for good lubrication at operating temperatures.

Always refer to your owner's manuals to select the proper viscosity oil for the ambient temperature and operating conditions at which the equipment will be used.

A multigrade oil provides good flow capability for cold weather but retains thickness for high-temperatures.