The Journal of the Society of Automotive Engineers
Drain every 500 miles
Regular periodic draining of crankcases will always be necessary. How frequently is largely in the hands of automotive manufacturers.
When good oils are used, frequency of draining is determined by the rapidity with which dirt and dilution occur. Most car manufacturers agree that at 500 miles there is enough dirt and enough dilution to make draining advisable.
The Sun Oil Company recommends that crankcase oil be replaced every 500 miles. Obviously, there is only half as much dirt present at 500 miles as there would be at 1000 miles; and the amount of dirt in an oil largely determines the rate of wear on working parts of the engine.
Improvements in lubricating systems which will minimize dilution and eliminate dirt will justify greater mileages before draining is necessary. In the meantime-even with Sunoco Motor Oilsdraining every 500 miles is the surest way to keep the grit content down to a point where you can safely forget about it.