It’s surprising how many people are reluctant to follow Ford Motor Company’s recommendation for specific motor oils for their vehicles. Either they don’t understand the engineering of modern lubricants or are clinging to things they learned about oil back when they first started to drive.
Let’s review the basics.
Engine oil performs many functions. It stops all the metal surfaces in the engine from grinding together and tearing themselves apart from friction and transfers heat away from the combustion cycle. Engine oil also holds in suspension all the nasty by-products of combustion like silica (silicon oxide) and acids. Finally, engine oil minimizes the exposure to oxygen and thus oxidation at higher temperatures. It does all of these things under tremendous heat and pressure.
The Society of Automotive Engineers (SAE) has established a numerical code system for grading motor oils according to their viscosity characteristics. SAE viscosity gradings include the following, from low to high viscosity: 0, 5, 10, 15, 20, 25, 30, 40, 50 or 60. The numbers 0, 5, 10, 15 and 25 are suffixed with the letter W, designating they are winter (not weight) or cold-start viscosity. The number 20 comes with or without a W, depending on whether it is being used to denote a cold or hot viscosity grade.
Kinematic viscosity is graded by measuring the time it takes for a standard amount of oil to flow through a standard orifice, at standard temperatures. The longer it takes, the higher the viscosity and thus higher SAE code.
The SAE has a separate viscosity rating system for gear, axle and manual transmission oils, and should not be confused with engine oil viscosity.
Because machined internal engine parts are more precise than the parts of 20 years ago, oils need to be thinner. Clearances between moving parts are smaller and more exact. Thinner oil such as 5W-20 can flow more freely through the engine while still filling the spaces. Thicker oil is harder to push through the spaces between the parts. This causes the oil pump to work harder, which in turn increases oil pressure while simultaneously decreasing oil volume. A lack of oil volume results in a decrease of lubrication and cooling, which may decrease engine part life.
Some customers are basing their oil usage on the incorrect assumption that Ford and other auto manufacturers only recommend 5W-20 oil in order to increase fuel economy. Using 5W-20 oil can increase fuel economy by about 6/10ths of a percent compared to 5W-30 and more if you are currently using a higher-viscosity oil. This equates to an additional savings of 125 million gallons per year when used in all applicable Ford vehicles. Since its introduction in the 2001 MY, 5W-20 oils have saved up to 640 million gallons of gasoline in the U.S. or an equivalent 5.6 million metric tons of carbon dioxide emissions.
Since any increase in fuel economy may not be noticed by the average motorist, the best reason to use 5W-20 oil is it’s thinner with lighter viscosity and creates less drag on the crankshaft, pistons and valve train. Additionally, the oil pump can move thinner oil more easily, improving oil circulation. The lighter viscosity of 5W-20 oil flows faster at start-up compared to higher viscosity oils, which helps reduce engine wear in critical areas by lubricating parts faster. Valve train components at the top of the engine require immediate lubrication at start-up.
Another oil misconception is that over-the-counter additives improve oil’s performance. We don’t recommend using oil additives and this is noted in the owner’s manual. The American Petroleum Institute (API) certifies that oils such as Motorcraft 5W-20 already contain the necessary additives for friction, detergent, etc. The addition of additives may actually interfere and react with the additives already present in the certified oil.
Hopefully this little refresher course in engine oil will help you better understand why Ford Motor Company and other automakers recommend certain oil for their vehicles.