1996 Ford F250 Owner's Manual - Page 322

Changing the Engine Oil and the Oil Filter Change the engine oil and oil filter per the following, whichever occurs first. Oil change intervals NOTE: Idling the engine for extended periods will accumulate more hours of use on your vehicles than is actually indicated by the mileage odometer. Consequently, the odometer reading can be often misleading when determining the right time to change your engine oil and filter. If you are using your Ford vehicle in a manner which allows it to remain stationary while the engine is running for long periods (door to door delivery, taxi, police, power/utility company trucks, or similar duty), then Ford recommends you increase the frequency of oil and filter changes to an interval equivalent to 200 ENGINE HOURS of use. Since most vehicles are not equipped with hourmeters, it may be necessary for you to approximate your idle time and plan oil/filter changes accordingly. 323