It is recommended that you change the oil in your passenger car or light truck every 7,500 miles. For diesel engines and turbo-charged gasoline engines, it is recommended to change the oil every 3,000 miles or every six months.
However, some vehicle manuals suggest that the 7,500-mile oil change is for vehicles that are driven under normal circumstances. Sever service driving includes frequent short trips (less than 10 miles), during cold weather, driving at sustained highway speed during hot weather, driving in dusty conditions, or stop-and-go traffic driving. If you drive under these circumstances, then it is recommended to change your oil every 3,000 miles or every six months. However, most oil companies suggest changing the oil every 3,000 miles or every 3-6 months, regardless of the type of driving you do.
New engines with little or no wear can probably get by with the 7,500-mile oil change, but as the engine accumulates miles, blow-by increases, dumping more unburned fuel into the crank case which dilutes the oil. This causes the oil to break down, and you could possibly end up with accelerated wear, as well as engine problems – loss of performance, increased emissions, and oil consumption.
It is highly recommended to have your oil filter replaced every time the oil is changed. Since most oil filters are now pint-sized, in contrast to the quart-sized filters that were once used, the smaller filters have less total filling capacity. The smaller filters were designed to save weight, cost, and space.
The oil filter’s job is to remove solid contaminates such as dirt, carbon, and metal particles from the oil before they can damage bearing, journal, and cylinder wall surfaces of the engine. Oil that is picked up by the oil pump is routed through the filter before it goes to the crankshaft bearing, cam bearings, and valve train. This efficiently removes contaminates and assures that only filtered oil is supplied to the engine.
Over time, the accumulated dirt and debris trapped by the filter can obstruct the flow of oil. The filter should be changed when it reaches this point, so that is the reason it is recommended to replace the filter each time the oil is changed. Waiting too long to replace the filter can result in damage from the filter becoming unplugged. To prevent this from causing engine failure, oil filters have a built-in safety device called a bypass valve. The bypass valve opens when the pressure drops across the predetermined value of the filter. When the bypass valve opens, oil can continue to flow to the engine. However, this allows unfiltered oil to enter the engine and contaminates enter the crankcase and are pumped through the engine. This can accelerate engine wear.
It is also a good idea to have your transmission, power steering, windshield washer, clutch, and brake fluids topped off when you get your oil changed. It should take no more than a half hour to have your oil changed, and most repair shops can do it on a walk-in basis, so there are no long waiting periods at the garage.