Oil Changes: How Often?

Do you really need to change your oil every 3 months/3000 miles?

I have been in the auto repair industry since 1972 ... hummmm, a simple calculation of the math illustrates that I have been in car repair for, uh, well, let's not go there. You do the math and keep it to yourself. At any rate, let's talk about oil change intervals.

For years the accepted oil change interval (as per carmakers) had been every 3 months or 3000 miles, whichever comes first. And why was that? It was because oils of yesterday broke down when left in the crankcase environment for longer than the prescribed interval. The combination of heat, friction, and the oil oxidizing over time resulted in an unholy clothing of the engine's internal parts called sludge.

As an automotive machinist for a good part of my career, I can tell you that sludge is an engine killer. Sludge takes a greasy, cake-like oily form and plugs oil return passages and acts like a sponge and soaks up good oil to grow its grotesque form, starving the engine of vital lubrication. Once established, engine heat crystallizes it to a hardened rock of ughhhhhh. I have spent many hours scraping and yes, sometimes chiseling established sludge from the inside of an engine before performing a machining operation on it! As the machinist prepares to perform a machine operation on a cylinder head, crankshaft, or engine block he/she must clean their work meticulously before performing the prescribed operation. If the sludge is not cleaned properly, the result will be a failed engine.

Why this lesson about sludge? Because without clean, high quality oil in your car's powerplant that used oil will develop sludge and cause premature engine failure. Now more than ever before, vehicle engines operate at high heat and close tolerances. The reason for this is the Federal Emissions mandates the government has imposed on the carmakers. Vehicles have to emit a smidgeon of the tailpipe emissions they did a decade ago. Carmakers have responded to the stricter regs by increasing combustion chamber temps with higher compression engines, running leaner fuel systems, adjusting ignition timing for optimum emissions, narrowing cooling system water jackets, and tightening engine oil tolerances. All this makes for hotter running engines that emit fewer emissions. Putting these more stringent demands on engines requires a lubricant that can stand up to this harsh environment.

Petroleum companies' work hand-in-hand with carmakers to develop engine lubricants to meet the requirements and demands of a particular powerplant, while still delivering the horsepower and torque that consumers expect. Cooperation in research and development between carmakers and petroleum companies has resulted in improved engine lubricants that properly lubricate your vehicle's engine as well as keep the inside clean of sludge buildup and – not incidentally – can go longer between oil changes!

A few years back, General Motors introduced a system called the OLM (Oil Life Monitor) system. This system had been in testing since 1984 and actually was put into some Buicks on a test basis. The goal of this system was to extend oil change intervals and attain bragging rights to having a more maintenance-free vehicle. The OLM monitors crankcase temp, moisture, and combustion chamber events (this represents the actual work the engine is doing while in operation). By closely monitoring these elements of engine operation the system can measure the serviceable life of the oil to within 10%.

After officially introducing the OLM with virtually no engine failures attributed to it, GM changed their service recommendations to what they called an 'Enhanced Maintenance Schedule'. With the Enhanced Schedule the motorist need only follow the dictates of the OLM and have other scheduled services done at prescribed intervals.

Ford Motor Company followed GM into the extended oil change interval march. In March 2007, Ford announced that they were revising engine oil change intervals to every 7500 miles. The reason? Quoting the article from the Associated Press:

"Not only are modern oils better, modern engines are also better. You don't have carburetors metering poorly on winter mornings, tolerances are a lot tighter, and operating temperatures are typically a little hotter, helping to cook off the junk that accumulates in the oil. Ford contends that its customers prefer a set amount of miles between changes. The automaker also cites the environmental benefits that come from less waste oil, monetary savings, as well as extensive tests as positive aspects of the new recommendation."

Yes, oil is much better than it used to be, engines are better protected with today's new lubricants but the same old logic still applies to the oil filter: always use a good quality filter when having the engine oil changed. The filter is the storehouse for dirt in the engine and when it doesn't do its job, the engine suffers internally. When dirt and grit are allowed to circulate over, within and on the engine bearing surfaces, cylinder walls, crankshafts, piston rings, camshafts and virtually all metal mating surfaces, they are damaged resulting in wider oil tolerances, lowered oil pressure and ultimately premature engine failure.

While I concur with R&D results over the years with respect to oil change intervals, I am still squeamish about leaving petroleum-based oil in an engine for 7500 miles. I guess I just know too much based on personal experience. Here are my revised oil change recommendations:

Change regular petroleum-based oils every 4000 to 5000 miles and synthetic oils every 5000 to 7000 miles. There, those of you that have criticized me for being in the back pocket of petroleum companies for recommending 3000-mile oil changes...are you happy now?

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