The time between oil changes depends a considerable amount on what kind of driving you do (Robert Couse-Baker, Flickr).

    by: Tom Torbjornsen | AOL Autos

    Have you ever tried to actually read your owner’s manual, especially the part about maintenance and service? As if this kind of stuff isn’t confusing enough, there are always two schedules listed, one for a vehicle driven under “normal” conditions and another for “severe.” But what exactly does this mean? I have yet to see an automaker that actually explains, in plain English, what these terms mean.

    So this article is the first in a series of four that addresses the differences between severe and normal service recommendations. We’ll start with the most common type of service, the engine oil change, and in subsequent articles move through the rest of the vehicle.

    Service Schedules for Oil Changes

    Let’s start by trying to understand the differences between normal and severe. The severe schedule, which always has shorter recommended intervals between oil changes, applies if any of the following are true:

    • Most trips are less than 10 miles (16 km). This is particularly important when outside temperatures are below freezing.
    • Most trips include extensive idling (such as frequent driving in stop-and-go traffic).
    • The vehicle is frequently driven in dusty areas, like on dirt or gravel roads.
    • The vehicle is frequently used for towing a trailer or using a carrier on top, both of which place extra demands on the engine.
    • The vehicle is used for delivery service, police, taxi, or other commercial applications

    If none of these conditions are applicable, you should go ahead and follow the normal schedule. Your owner’s manual will tell you the specific mileage suggestions for the engine in your vehicle, but make sure you have identified the correct engine, as many models have more than one. Keep in mind that the “rule of thumb” 3,000-mile oil change interval recommended by many oil change shops is an aggressive schedule that is likely to correspond with the car manufacturer’s “severe” category. It’s clearly in an oil change shop’s best financial interests to recommend frequent oil changes, but many manufacturers suggest 5,000-mile or even longer intervals under normal conditions.

    There’s also a wildcard in the mix, which is that plenty of vehicles today have an engine oil life monitoring system. These work by monitoring the crankcase temperature, combustion chamber events (the work the engine does), and the time since the last oil change, and then using a computer algorithm to come up with an approximate percentage of usable life left in the oil. Under the right combination of events, these systems can recommend an oil change ahead of the service interval in your owner’s manual. Specifics for these systems vary from carmaker to carmaker, but overall, they are very accurate. If your oil life monitoring system says it’s time to change the oil, then you should do so regardless of mileage. Remember that the monitor needs to be reset every time you have an oil change, otherwise the system will be thrown off.

    In The Real World

    So let’s take a look at those severe schedule recommendations and try and figure out what they really mean. One of the biggest reasons why you’d use the severe schedule is if your daily commute is a short one, just a few miles across town, with plenty of stop signs and traffic lights between home and work. This sort of driving can be hard on oil because the engine isn’t allowed to completely warm up to operating temperature, especially during the winter in cold climate areas.

    When the engine is cold, it operates in a mode that richens the fuel mixture, which causes excess fuel to spill down past the piston rings and into the crankcase. This dilutes the oil and breaks down its chemical fortifying packages, ultimately diminishing the oil’s ability to flow. This change in viscosity decreases the oil’s capacity to protect the internal engine parts, and to resist vaporization and oxidation. Other damaging effects are acid buildup and ash, causing further viscosity breakdown as well as internal sludging.

    If you don’t understand what all these things are, suffice it to say that they’re bad for your engine and can lead to premature failure of internal engine parts. Trust me when I say you do not want to pay for an engine rebuild.

    The other thing that really suggests you use the severe cycle is if your engine is driven hard. You’ve probably heard used car sellers say, “But all those miles are freeway miles,” to describe a high-mileage vehicle. There’s truth to the fact that highway mileage is easier on an engine, because it doesn’t take a lot of power to maintain 70 miles per hour on the highway.

    Driving a vehicle that’s heavily loaded or towing a trailer -- or even just driving aggressively -- puts a much greater strain on the engine. When an engine is taxed from heavy loads, internal operating temperatures rise, causing evaporation and oxidation of the oil. This results in heavy “oil use” as well as caking and sludging. Oil use is different than oil burning. Instead of the oil entering the combustion chamber and burning, it evaporates through the breather system. The other condition, called oxidation, causes heavy internal sludging. Sludge is a heavy, oily, cakey substance that bakes onto the inside of the engine. Sludging starves the engine of lubrication because it soaks up the oil like a sponge as the oil passes over this unholy substance.

    The other thing to be careful about is driving in a perpetually dirty environment. When an engine operates in an environment where fine dust and dirt is constantly fed into the air intake, this dirt eventually finds its way into the oil. This thickens the oil, which can become abrasive, causing internal wear. In addition, the dirt scrapes the sides of the cylinder walls, causing abrasion of the combustion chamber walls. If you live in the city and only rarely encounter an unpaved road, you shouldn’t worry about it when you do. But if you live in a rural area with plenty of dirt roads, the severe schedule is for you.

    The 100,000-mile Interval

    How often do you change your oil?

    The following is an interesting story that illustrates how “normal” driving conditions affect engine oil longevity. About 12 years ago when GM officially launched its Oil Life Monitor, a caller to my radio show, America’s Car Show, asked me about the accuracy of the new system. My answer at the time was that I didn’t trust it. Shortly after the program ended, I received an e-mail from a concerned GM engineer who was on the team that developed the system’s algorithm. He said I didn’t know what I was talking about, which led to a conference call with the GM engineering team. They spent two hours enlightening me and I’ve been a believer ever since.

    But what left a lasting impression was when they told me that they used an early ’80s Corvette for testing the new system, driving that car over 100,000 miles on the same oil without any serious engine damage. How could this be? By maintaining some simple operating parameters:

    • The car was primarily driven on the highway at highway speeds of 55 mph or higher.
    • The engine was run at least 20 miles each day.
    • The vehicle did not tow or carry heavy loads.
    • Crankcase temperature was kept consistently at 200 degrees Fahrenheit.
    • The vehicle was always operated in a clean environment.

    While I wouldn’t suggest you try going 100,000 miles between oil changes, it’s clear that if you operate your car under the right circumstances, there’s no need to change your oil every 3,000 miles.

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    1 - 20 of 204 Comments
    joemedic2005 Oct 24, 2010 4:40 PM
    I have been an auto enthusiast for 35+ yrs. as well as having ASE training but never pursued being an auto tech in earnest. I have fixed,repaired,replaced and rebuilt just about everything on a vehicle. This is just plain fun and therapy for me. As far the Oil changes are concerned years ago oil technology & engine technology was no where as good as it is today. this is why oil needed to be changed at 2000 to 3000 miles and most of the time using 10w-30 or 10w-40 oil. Today we have better oil tech. we even now have synthetic oil. engine tolerances are much tighter now that is why we most auto mfgrs. use 5w-10 or 5w-20 oil. Changing your oil filter with the oil is also paramount. we now even have different filtering quality levels now. But just remember this, The oil is the " Life Blood " of the engine. proper changing and maintainanence of it is very importantant. You should not go over 5000 miles on the oil if you use standard oil. I use synthetic oil for all of my cars and change the oil and filter every 4000 to 5000 miles no more. I have yet to have any of my cars burn any oil or not exceed over 100,000 miles. Not even any valve knocks as best as I can recolect. A little preventative maintainence at the begining will save you a lot of money later. auto mfgrs. want you to change your oil at 7000+ miles in hopes that you will have issues so they can try to make money in there shops or to try and get you to purchase a new vehicle.
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    mullaney2006 Oct 24, 2010 3:55 PM
    After reading my GMC Envoy's service manual, it offers certain guidelines on getting the oil and filter changed (can't remember off hand whether it's 3,000 or 5,000 miles, but that's besides the point). HOWEVER, if I were to follow the "engine oil life" percentage that is shown on my dashboard display I wouldn't have to change my oil for AT LEAST every 6 months to a year! Why did the manufacturer bother putting this feature in if the difference between the display and their actual recommendations is so far off?
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    dgibson969 Oct 24, 2010 3:36 PM
    I'm surprized that you didn't recommend using a quailty engine oil? Many of these oils today, are being formulated with less and less ZDP! Also synthetics offers far greater protection, esp if your use an ester based oil like redline or amsoil. Mobile 1 is my favorite the fully sysnthetic, but they too have begun using a hydrocraking method of petroleium based stocks which is cheaper and not as good as the ester based oils.
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    dannjillbain Oct 24, 2010 2:30 PM
    cliff2856 Jul 07, 2010 6:38 AM "Good advice overall. Also, I wonder what type of oil GM used in that 100,000 test. Full synthetic is my guess." No synthetic in my Diesel truck and it can go over a year before it signals for a oil change at which point I just change the filter.
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    dannjillbain Oct 24, 2010 2:26 PM
    Owners manual in my '05 Chevy diesel truck says that the oil monitor my not signal for an oil change for over a year, then to just change the filter. It has done just that twice. It still runs like new. It stays outside and faces north all winter long. It still starts as fast as a car.
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    brdsng84 Jul 30, 2010 9:08 PM
    When my beloved Mazda MX6 had about 110K miles on ************** having "O" ring problems and burnt oil to the point it looked like my block was about to burn down every morning when I started it. Garage guy told me, eventually the engine will "blow". So just to be I on the safe side, I asked him what exactly do you mean by "blow"...........is it going to explode or catch on fire or am I just going to lose power and coast off the road and call a tow truck??? Oh, he said it will just "die" and you'll lose your motor power. I could handle that, so...I would buy the Synthetic high mileage engine oil and check it every 3 days, when the oil was low, I'd add a quart or two. Had to do this about once every 2 weeks unless took a long trip etc. Needless to say, I ran that great car till it had 151K plus miles on it. AND it probably would have lasted another 50K had I not been in a head on collision that totalled it at that 151 K milage. What a car. I had the oil filter changed a few times over the years but never a change since it was always clean oil from adding it so frequently. And it really didn't have much more expense than taking it to the garage to have the oil change done every 5K miles.
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    ertruitt Jul 30, 2010 8:54 PM
    Our new car comes with the oil changes and tire rotations and they say 3,750 miles...and since it is part of our package that the mfg came with the vehicle..think I will stick with that no matter.
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    ty2010 Jul 30, 2010 8:12 PM
    ski87rc, yes the vette had a chevy 350, but it was very unlike a stock. Gated pans, likely a dry sump plus it's designed to run at higher rpms than other applications which keeps the oil flow higher, which means it's less likely to leave sediment and less likely to sludge up on the hot spots. ---------------------------------------------------------------------------------- Diesels generally have a lot more oil capacity and are designed for heavy duty application, so the longer applies unless you are actually doing very heavy duty towing. If however you just run detergent 30 weight, you will have to use the shorter schedule as diesel specific oils have a lot of buffer chemicals to keep it from turning acidic ----------------------------------------------------------------------Mercedes listed as 13k oil changes is appropriate for synthetics. They have larger oil filters than most, they have super tight tolerances so there's less blowby and they also do more modeling to eliminate hot spots in the engine that thermally break oil down.----------------------------------PCV valve, if the hose does not fit snug, replace it. Whatever you do, do not fasten the PCV hose with clamps, if your engine misfires it will blow out oil gaskets rather than simply separating the hose. Replacing those gaskets is a lot more money, plus if a serious oil leak develops because of that serious engine damage can occur.------On old beater cars I change the filter anually and change oil every couple years if it needs it or not, usually not as they usually consume a little more oil.
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    dviner5967 Jul 30, 2010 7:53 PM
    if you use synthetic oil its a man made product you can go at least 15,000 miles between oil changes spin on a new filter about every 7,000 miles do not use a cheep filter a paper filter element stops working as soon as its saturated use a fiberglass element filter mobil 1, wix ect. stay away from fram weak anti drain back vavles the filter is the most important part on a engine to keep it clean
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    ace1026 Jul 30, 2010 7:48 PM
    I have under the recommended 3000 mile change but have exceeded the date for a change by 2 months. Is it necessary to change the oil because of the date. Thanks, Jerry
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    nosrepsan Jul 30, 2010 7:47 PM
    I'm retired military, my cars have gone with me over seas, Germany, Italy, Japan. I was once told by and oil engineer: You change your oil & filter, when you can no longer see through ************* burnt or like gasoline, it is gritty or no longer feel slippery. New oils, additives and car engine designs make it possible to run 7,500 or more miles. I change both at or near 10,000 miles, I have had eight vehicles and never had a problem, a Ford Fairmont had over 150,000 miles and I drove it ************* in the radiator while in Germany, because of a cracked intake manifold - which leaked water into the carburetor making the antifreeze burn and smoke smelling like perfume, I drove it 6 months like that before one of the Base Exchange Car dealerships took off my hands.. Still running.
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    alfredschrader Jul 30, 2010 7:27 PM
    I really never change the oil in my 1986 Camaro V8 and now it has over 200,000 miles on it. But, here is another true story (people that know me, know I tell the truth). I had a 1970 200 C.I. 6cyl Mustang coupe I bought from a mechanic who had just rebuilt the motor. He forgot to torque the connecting rod bolts on cyl number one. After a few thousand miles it let go on me and made a hole in the cylinder block inwhich it then became a 5 cyl motor with Zero oil pressure. So, I patched the hole & put a grease fitting on the main oil galley & pumped in two full sleeves of high-temp wheel bearing grease essentially greasing everything in the motor. I drove that car around town for two weeks with Zero oil pressure. It's a true story....Al-
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    eric0362 Jul 30, 2010 7:01 PM
    I use Amsoil and a Boch high capacity filter once a year or 24000 which ever comes first. Save money, time, environment.
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    fmazoman51 Jul 30, 2010 6:35 PM
    I used to change at 3000m with conventional oils, but now just run syn oils. I go a bit longer with that stuff. A few weeks ago I was at WallyWorld (the only things I buy there are oil and filters and some fishing stuff). Walked by an endcap and what do I see? A whole rack full of 5qt jugs of Pennzoil Ultra Syn, for $10 each on clearance. Had a heck of a time pushing a FULL cart of oil to the checkout.
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    emunoz1390 Jul 30, 2010 6:29 PM
    wwalter420, with all that money you spent on oil, you could have bought a new car.
    Report This
    jkayesimp Jul 30, 2010 6:11 PM
    Car Talk had an example of when a U.S. citizen had there car shipped to England when they were relocating there. They took their car in after 3,000 miles for an oil change and they laughed at them. The mechanics stated that with cleaner fuels, better oils, and more efficient engines that cars did not need oil changes every 3,000 miles and that Americans were being "suckered" by the car dealerships. I split the difference and have it changed around every 7,000 miles......The "mothership" ******* 100,000 miles with no problems.
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    sweetfreddie Jul 30, 2010 5:58 PM
    I may be old school but I have owned a 1988 Mercury Grand Marquis since it was new. It now has over 274,000 miles and continues to run with no problems. I have always changed the oil at 3,000 miles. Mechanics have told me that engine gunk builds up in the oil and the longer you wait to change it the more wear you put on your engine. That makes sense to me. I beleive in the mechanic's saying "You can pay me now or pay later".
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    killkubota Jul 30, 2010 5:56 PM
    You forgot a very important point in the oil change advice. If you have a TURBOCHARGER like my POS Volvo did some years ago, change the oil every 3000 miles religiously. If you don't, you'll be stuck with a $2000 repair bill two or three times during the life of the car. No kidding. Turbos need clean oil. Without it, they will fail very quickly. Never, ever buy a Volvo. You will regret it.
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    se72748 Jul 30, 2010 5:54 PM
    I have excellant results changing oil every ten thousand miles.Suit yourself ,but, I belive any less then 10,000 is frivilous waste
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    rwonnieb1935 Jul 30, 2010 5:46 PM
    Chang the AIR FILTER on the carb. that is where the DIRT comes in. too
    Report This
    1 - 20 of 204 Comments
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    This article is the first in a series of four that addresses the differences between severe and normal service. We’ll start with the most common type of service, the oil change.


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