I noticed there is a lot of confusion on this forum about the proper engine oil type or viscosity someone should use in their vehicle. I have put together a short statement to clarify the issue for the many of you who do not have the experience in professional engine repair or design to help understand why it is important to use the correct type of oil in your engine.
There are two main reasons why vehicle manufacturers recommend thinner or lighter viscosity grades of motor oil. First, a gain in fuel economy can be achieved with lower viscosity oil. At cold temperatures and at start up, lower viscosity oil will reduce internal engine friction. About 10% of the engine's horsepower is lost to internal engine friction, resulting in a drop in fuel economy. Additionally, vehicle manufacturers are struggling to meet Corporate Average Fuel Economy (CAFE) requirements set by the government and avoid paying associated fines. Any fuel mileage improvement associated with a lubricant use would be good for them, and lighter viscosity grade motor oil will make a difference.
Second, thinner motor oil is essential for easy starting, particularly in cold weather, and for proper lubrication once the engine starts. Today's smaller engines have smaller clearances and tighter tolerances between moving parts, and there have been some instances where camshaft damage has occurred because of inadequate lubrication with higher viscosity grades in colder weather. Thinner oils, such as SAE 5W-30, will flow faster than heavier motor oils during start-up and initial engine operation and will help protect the engine from excessive wear. Multigrade oil will also offer the same high temperature protection as single grade motor oil. Always check your vehicle owner's manual to select the proper viscosity grade based on the expected temperature range.
The viscosity grade(s) recommended by the vehicle manufacturer depend somewhat on engine design. Engine manufacturers have spent considerable time and expense experimenting with different viscosity grades and have indicated in the owner's manual the grades they feel will best protect the engine at specific temperatures. While one manufacturer's engine may require an SAE 10W-30, another manufacturer's engine may require an SAE 5W-20 viscosity grade. This is likely due to different tolerances within the engine or other engine design factors.
There are two main reasons why vehicle manufacturers recommend thinner or lighter viscosity grades of motor oil. First, a gain in fuel economy can be achieved with lower viscosity oil. At cold temperatures and at start up, lower viscosity oil will reduce internal engine friction. About 10% of the engine's horsepower is lost to internal engine friction, resulting in a drop in fuel economy. Additionally, vehicle manufacturers are struggling to meet Corporate Average Fuel Economy (CAFE) requirements set by the government and avoid paying associated fines. Any fuel mileage improvement associated with a lubricant use would be good for them, and lighter viscosity grade motor oil will make a difference.
Second, thinner motor oil is essential for easy starting, particularly in cold weather, and for proper lubrication once the engine starts. Today's smaller engines have smaller clearances and tighter tolerances between moving parts, and there have been some instances where camshaft damage has occurred because of inadequate lubrication with higher viscosity grades in colder weather. Thinner oils, such as SAE 5W-30, will flow faster than heavier motor oils during start-up and initial engine operation and will help protect the engine from excessive wear. Multigrade oil will also offer the same high temperature protection as single grade motor oil. Always check your vehicle owner's manual to select the proper viscosity grade based on the expected temperature range.
The viscosity grade(s) recommended by the vehicle manufacturer depend somewhat on engine design. Engine manufacturers have spent considerable time and expense experimenting with different viscosity grades and have indicated in the owner's manual the grades they feel will best protect the engine at specific temperatures. While one manufacturer's engine may require an SAE 10W-30, another manufacturer's engine may require an SAE 5W-20 viscosity grade. This is likely due to different tolerances within the engine or other engine design factors.
(the only reason you still have water in the radiator is because it's a presurized system). Also engines require a bit more lubrication than water can provide (although you are absolutly right that water can act as a lubricant.....try hitting the brakes hard in the rain to learn that one).
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