Kia Optima 2004 Owner's Manual page 223

RECOMMENDED SAE
VISCOSITY NUMBER
NOTICE :
Always be sure to clean the area
around any filler plug, drain plug, or
dipstick before checking or draining
any lubricant. This is especially
important in dusty or sandy areas and
when the vehicle is used on unpaved
roads. Cleaning the plug and dipstick
areas will prevent dirt and grit from
entering the engine and other
mechanisms that could be damaged.
7-38
MAINTENANCE
Engine oil viscosity (thickness) has an
effect on fuel economy and cold weather
operation (starting and oil flow). Lower
viscosity engine oils can provide better
fuel economy and cold weather
performance, however, higher viscosity
engine oils are required for satisfactory
lubrication in hot weather. Using oils of
any viscosity other than those
recommended could result in engine
damage.
When choosing an oil, consider the range
of temperature your vehicle will be
operated in before the next oil change.
Then select the recommended oil
viscosity from the chart.