Oil change intervals are one of the most disputed topics in the automotive field. Recommendations from 3,000 up to 20,000 miles are common. Mileage recommendations, without regard for long-term results, are irresponsible. Driving conditions and not mileage, determine oil change needs.
Oil change recommendations may not be based on the vehicle owners' best interest
Most recommendations I have seen, do not take the overall lowest cost of operation, for the vehicle owner into account. Misleading claims and false information are very prevalent. The facts are these:
An oil change interval should be based on driving conditions. Mileage is NOT a reliable indicator of oil condition
Oil does far more than lubricate the engine. Additives, which prevent wear, protect catalytic converters, reduce corrosion and keep seals pliable, diminish with use. Liquid contaminants enter the oil in operation, and changing the oil is the only way to remove them. This harmful waste passes right through the oil filter.
They recycle virtually 100% of oil, changed by professionals. It provides a large amount of heating oil, at much lower environment impact, than producing it from crude. The impact from worn piston rings, leaking seals and oil burned by damaged engines is huge and increased by neglecting oil changes.
Driving conditions and not mileage
I take a driving vacation and travel 3,000 miles in two weeks. My average trip is about 250 miles at highway speed. The engine oil is still fine and will easily go many more miles. Changing this oil will provide no benefit.
When I return to work, the drive is about five miles in stop-and-go-traffic. My car sets all day and is not run. In the evening, another five-mile trip takes me home. We exhaust the oil, in 3,000 miles, under such conditions. Additional driving, with worn out oil, damages my engine. Mileage is simply not a reliable indicator.
Time is also a consideration with engine oil, especially if the vehicle is only driven for short trips. Moisture will accumulate in the oil and produce corrosion and sludge. Properly draining the oil, helps remove most contaminants. Replacing the engine oil twice annually, on vehicles that do not get driven, should be considered a minimum.
Oil does more than lubricate
Additives in engine oil help keep seals pliable, preventing leaks and expensive repairs. Depleted oil greatly increases seal failure. As protection diminishes, seal and gaskets get hard. Soon they fail to seal, and leaks develop. Replacing a rear main seal may cost more than $1000.00. Valve cover gasket replacement is also very expensive. These costs quickly surpass any savings from extending oil changes.
Engine oil operates hydraulic tensioners and variable cam timing devices. To do this, the viscosity must be exact. This is why they require very specific oil in modern engines. Depleted oil that contains contaminants, changes viscosity. Check engine lights and expensive repairs result from oil that is too thick or thin to operate properly.
Catalytic converter damage may also result from improper oil viscosity. Depleted and contaminated oil is more volatile than fresh oil. These fumes burn in the catalytic converter(s) and may raise temperatures to dangerous levels. Converter failure is far more common on vehicles with depleted, contaminated and improper viscosity oil.
Liquid contaminants damage an engine
Short trips, less than ten miles, are extremely hard for an engine. This is far worse in cold, very hot or humid conditions. Start a cold engine and moisture forms in the crankcase. Corrosion additives in the oil, contain this moisture and protect the metal engine components.
Reaching and holding full temperature, normally about 25 miles or more, allows heat to boil this moisture. The PCV system draws the moisture, which rises as steam, from the engine. On short trips this does not occur. Oil is soon saturated, and the moisture attacks the metal components and forms sludge.
All vehicle manufacturers consider short trips as an extreme service. They recommend frequent oil changes, around 3,000 miles, under these conditions. This is the way most vehicles operate. Driving in cold (30' Fahrenheit or below), very hot (90' Fahrenheit or above) and humid conditions are severe service. Other conditions include, stop and go driving and idling. Most city drivers, operate in this manner daily.
Other liquids that enter the oil may include coolant, from internal leakage and fuel that gets around the piston rings. They design oil filters to remove solid particles from the lubricant. Liquid-contaminants travel through the filter. A proper oil change drains these contaminants and sludge from the engine. New oil also replaces the additives that protect the engine.
Why are longer oil change intervals pushed?
Solving problems requires time, understanding and study. Giving the impression of helping requires none of these, if no one checks the long-term results. Reducing the use of oil is a desirable goal. Understanding how an engine works and all the factors involved in lubrication and protection requires knowledge and study. Policy makers may demand longer oil change intervals, although this increases the use of oil and other costs in the long-term. They give the impression of action, not responsible for the problems created.
To help enforce short-term thinking, they often rate vehicles on maintenance requirements. Less maintenance equals a better rating. Extending oil change recommendations appears to decrease maintenance, since the long-term costs are not considered.
No one wishes to waste oil or spend money needlessly. However, drivers face the costs of reality many policy makers lack. The vehicle owner will pay the responsibility of overall costs. Pennies saved on extended oil-changes, may result in hundreds of dollars in auto repairs and vehicles needlessly scrapped. Vehicle owners pay the costs of poor decisions. Drivers can lower costs, by basing oil change intervals on driving conditions, and not a mileage recommendation.