What whyireef said is valid to a point. Unfortunately, many of us are held hostage to what our fathers believed in and what we have been told was right and true. Like so many other things in todays' world what we thought we knew is either no longer valid or simply does not apply.

Better metallurgy, superior manufacturing capabilities, closer tolerances, advances in fuel technology and government mandates restricting sulfur levels in conjunction with superior oil basestocks, and exceptional advances in additive technology, collectively trump the shameful promotion of 3k oil changes to the masses by quick change facilities and old school mechanic thinking that the oil must be changed at short intervals.

In industry, it has been proven that time based oil changes are an opportunity to introduce contamination, exposing a unit to substantial wear it would not have seen, had the oil been properly managed and monitored. Condition based oil changes are now a generally accepted practice in equipment and machinery with values far exceeding that of any automobile.

Internal combustion engines, be they compression or spark ignited create challenging conditions for today's lubricants. That said, today's lubricants are up to the task, designed to seal, clean, cool, resist corrosion, and reduce wear, they are designed and built to perform and protect. They do however have their limits.

Would you throw out a set of tires if they still had useful life as seen by the tread depth? The engine oils have a job to do and in the majority of applications where high quality lubricants are used (the big ? being what constitutes high quality) they are being discarded needlessly and wastefully as they still have additional life in them. We change oil in the majority of cases to satisfy a need that is perceived as the right thing to do but in the big picture (total lifecycle of the unit) adds no value.

The only true way to measure the optimum life of an oil is by using oil analysis and trending the results. Every application, every engine, gearbox, hydraulic system, air compressor, turbine etc., has its own unique wear rate which is directly related to the quality of the lubricant, the maintenance practices of the caretakers, the environment it is in and the demands that are made on the machine. We always want to change good oil, never "bad" or dirty oil, hence the reason for periodic oil changes. But these change intervals, many steeped in history and based on the "we always did it that way" thinking or "oil is cheap compared to parts" reasoning ignore the fact that we willfully throw away a valuable resource without hesitation many unknowing that substantial life is left.

The concept that changing oil early in an engine will do damage is foreign to me. Damage is being done to the environment, not the engine. However it must be said here that if the engine oil is not kept clean and proper storage and/or handling of the engine oil is not exercised, whyireef's point about damage is a valid one. Spectrometric analysis of engine oil and the interpretation of the results is left to professionals that understand the lubricant chemistry, the functions of various additives and any pecularities related to the specific application and its history.

The short story is change the oil in a (not too short) timely fashion and don't give it another thought, the facts though support the reality that changing the oil at 3 times longer what most people think is reasonable will have no negative impact on the unit in its typical lifespan. But the reality is one never knows what the appropriate interval is without an oil analysis program.