Oil Change Intervals


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With over 35 years of automotive experience, Tom makes learning about cars easy. Get more of his advice:

    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. It makes me depressed. You do the math and keep it to yourself. At any rate, enough about my mid life crisis. Let's talk about oil change intervals.

    For years the accepted oil change interval (as per the carmakers) has been every 3 months or 3 thousand miles, whichever comes first. Why? Because the oils of yesterday degraded and 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 lubricants. Once established, engine heat crystallizes it to a hardened rock of ughhhhhh, I have spent many an hour 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, engine block or the likes 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 good quality oil in your car's engine, it 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 risen to this occasion 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 less tailpipe emissions. Putting these demands on engines requires a lubricant that can stand up to this harsh environment. Hence, petroleum companies' work hand in hand with carmakers to develop engine lubricants to meet the requirements and demands of a particular powerplant, still delivering the advertised horsepower and torque output that consumers expect. 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 CAN GO LONGER BETWEEN OIL CHANGES!

    A pioneer in extending oil change intervals ...
    A few years back, GM 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? 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 it the OLM, GM changes 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 has followed GM into the extended oil change interval march. Four months ago (March of this year) Ford announced that they are revising engine oil change intervals to every 7500 miles. The reason? Quoting the article from the Associated Press dated March 22nd, 2007:

    "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.

    So while yes, I have revised my thinking regarding extending oil change intervals:

    Here are my revised oil change recommendations: change regular petroleum based oils every 4-5 thousand miles and synthetic every 5-7 thousand miles.

    There, those of you that for years have criticized me as being in the back pocket of petroleum companies for recommending 3 thousand mile oil changes, are you happy now?

    'Til next time ... Keep Rollin'

    Recent Comments

    1 - 10 of 1355

    Trailertrash124 01:13:29 AM Aug 31 2008


    Ictus in AZ 01:03:33 AM Aug 31 2008

    Christie15Luv needs to have her oil changed. And, I mean that sincerely.

    Mushmeat2 01:02:14 AM Aug 31 2008

    i change my old lady's oil every night , takes about 11 min she runs smooth except for a heavy squeel lol

    Nutty4U23434 01:01:24 AM Aug 31 2008

    Anyone own a 95 Saturn SL? I'm using or leaking oil. Can't find the source. Don't understand the difference in 10W40 or 5W/40 which is the best to use in an auto with high milage?

    Mushmeat2 01:00:20 AM Aug 31 2008

    iI have a 2005 Harley Davidson , change oil every 2500 miles, at 16.000mi, engine needs help. smokes and is gutless. No suprise here

    Mushmeat2 12:56:51 AM Aug 31 2008

    I have a 2002 chevy blazer i drive mainly highway , i change oil every 10,000 miles runs great have 175,000 miles so far , no trouble

    DDouglasKerr 12:48:24 AM Aug 31 2008

    I have a GMC Envoy, I change the oil when the light comes on which has been about every 11,000 miles.

    Jvthomas 12:46:34 AM Aug 31 2008

    ok..hold on to your wallet..I'm a amsoil dealer going on to 30 years..we as a company have posted the 25k mile oil change since the beginning of the company..plus as a ex air force inspector trained in oil anaylsis..using a spectro unit to read the amount of metal in oil..and reaching the limits of metal in oil which can give the info needed to change oil before damage to equipment..I'm now at 20k miles chev 3/4 ton 6.0 motor..19.5 miles per gal using amsoil..jvthomas@aol.com..in the past few years I ran a honda 1.8 motor for 45k before a change of fluid...contact me, I can help you to save a lot of money..side bar..amsoil will warr the use of oil in all motors etc..just the facts contact me asap jim

    Christie15luv 12:30:49 AM Aug 31 2008

    McCain picked her because she's a woman and wants to get the women to vote for him. He did what Obama should have done, gone with Hilary to get the woman voters. Too bad Obama didn't get the message. I hope it doesn't cost him the presidency. Women want to be represented in the White House, and Hilary was the best woman for the job. I just hope whoever gets elected does a good job. If they don't, we shouldn't give them another term like Bush. I just don't understand why people give a jerk another term. Such a disaster the past 8 years have been for our country.

    MiDose 12:11:15 AM Aug 31 2008

    When GM started using catalytic converters, they extended oil change intervals. The owners manual in my 94 Chevrolet Suburban says 7500 mile oil changes. I normally do change approximately 5000 miles but have occasionally gone over 7500. The car now has 340,000 miles and in all that time the valve covers have never been off it. It now consumes a quart every 2500 miles or so. A side note though, at 250,000 miles I had to change the first tail light bulb as well, at 300,000 I had to change a headlight bulb. Those are my more major repairs other than warped front brake rotors which get turned about every 25,000 miles.

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