Grease is the word: a guide to oil and your carWritten by Nick Shultz | | firstname.lastname@example.org
Lubrication engineers tell us that the moving mechanical parts within our engines should be separated by a thin film of oil. Theoretically, the only time that any significant engine wear should occur is during engine start up. During cold engine startup, the crankshaft and other internal engine parts rest against one another until the engine’s oil pump has delivered enough pressurized oil to create a barrier between the moving parts. This can take a few seconds after initial engine startup.
The amount of internal engine wear that can occur during startup is significant. Therefore, manufacturers have recommended the use of thinner engine oils which reach internal engine parts sooner after startup.
As long as engine oil is maintained and no dirt is allowed to build up within it, oil should perform its primary tasks quite well throughout its life span.
Engine oil has several primary tasks. Various additives are mixed into the basic lubricant so that engine oil can perform multiple tasks. Besides acting as a lubricant, engine oil also acts as a sealant. It helps prevent combustion gasses from entering the crankcase. Oil aids in internal engine corrosion resistance. Additives within modern engine oils help prevent an engine corroding from the inside. Those very same additives are what cause oil to “stick” to engine parts.
Oil has additives which help keep it from foaming within the crankcase. As the crankshaft spins within the engine and oil is slung inside the crankcase the oil has a tendency to foam. Aerated oil cannot be readily picked up and transferred by the oil pump. Therefore, anti-foaming additives are added to the oil to help prevent this condition from occurring.
Detergents and dispersants are added to oil to help keep small dirt particles suspended within the lubricant. If those particles are large enough they will be trapped by the engine’s oil filter as the oil passes through it. If the suspended particles are too small to be trapped by the engine’s oil filter then they will not be removed from the oil until the engine oil is replaced. This is one of the primary reasons we should replace our oil on a regular basis. Engine oil undergoes thermal breakdown at high engine temperatures. At these high engine temperatures, oxygen and oil chemically react with one another and mix with moisture trapped inside the crankcase which then creates a gummy black mixture called sludge. Sludge can block oil passages and deteriorate the engine’s lubrication system to a point where serious engine damage can occur. The detergent additives added to modern oils helps to dissolve the sludge and then suspend it within the engine oil. It is these suspended dirt and varnish particles that make our oil appear black.
Viscosity by definition is an oil’s resistance to flow. It is basically, although not literally, the thickness or the body of oil. Engine oil must be able to flow in order to lubricate. At very low operating temperatures, oils by nature, do not flow very well. Additives are added to oil to make them flow better at lower temperatures.
The Society of Engineers (SAE) and the American Petroleum Institute (API) established guidelines years ago for oil flow performance. Today we simply refer to these established standards as an oil’s viscosity index rating. Most modern engine oils have a number that looks something like this: 10W30. The first number before the “W” indicates the oil’s flow characteristics at zero degrees and the number after the “W” indicates the oil’s flow characteristics at 212 degrees Fahrenheit. The “W” itself simply means that the oil was tested at zero degrees Fahrenheit and often is referred to as “winter weight” oil. If there is only one number and no “W” is present then the oil was only tested at 212 degrees Fahrenheit.
The lower the number is before the “W” the better flow characteristics that oil has at low temperatures. The higher the number after the “W” the better flow characteristics the oil has at operating temperatures. Most modern day engines require engine oil that has a Viscosity Index of 5 W 30. However, check your owner’s manual for the manufacturer recommended oil viscosity.
If you have ever heard that short trips are harder on a car than highway driving, you heard correctly. When a vehicle is not driven at operating temperature for any length of time. the moisture within the engine never has an opportunity to fully boil out of the engine. The water then mixes with the engine’s oil and creates some very nasty chemicals which can rapidly destroy our engines. Therefore, vehicles that may never be driven out of the city must follow a different maintenance schedule then those cars that have a combination of highway and city driving on a regular basis.
Oil change intervals
Vehicles that are driven primarily around town and that rarely see highway use should have their oil changed at 3,000 mile intervals. As I stated earlier, city driving is the hardest on engine oil.
For vehicles that are driven a combination of city and highway miles on a regular basis then 5,000 mile intervals should be adequate between oil changes. Finally, for those vehicles that are driven primarily on the highway and very little in town most oil manufacturers recommend that the engine oil should be changed every 7,500 miles.
Of course, if you operate your vehicle in dusty environments or at extreme temperatures, then you should change your engine oil more regularly.
It is also much better to change your engine’s oil when your engine is at operating temperature. When your oil is at temperature you are more likely to purge the engine’s crankcase of unwanted sludge and dirt particles.
I have briefly discussed engine oil this week. There is much more to engine oil than I was able to cover in this short piece.
I am always available to field any questions you may have regarding any automotive related topic, including engine oil.
Next week I will discuss conventional engine oils versus synthetic engine oils.
Nick Shultz is an instructor of Automotive Technologies at Owens Community College. He is an arbitrator for the Better Business Bureau who specializes in cases involving the Ohio and Michigan Lemon laws. He is a certified master automotive technician by ASE, General Motors Corp. and Ford Motor Co. E-mail your auto questions to email@example.com.