• Jul 7th 2010 at 12:00AM
  • 203
The time between oil changes depends a considerable amo... The time between oil changes depends a considerable amount on what kind of driving you do (Robert Couse-Baker, Flickr).

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

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 Second Ago
      Yale Mosk
      • 8 Months Ago
      When I purchased a used Lexus from the dealer, part of the deal was that they would do the 30,000 mile service free (about $400). I watched the mechanic and all he did was change the oil & filter and look around the car. When I confronted the mechanic, he said that is all the normally do. The long list they give you is all BS.
      • 8 Months Ago
      You know in today’s world with labor rates going up along with part prices it seems cheap to me to change oil every 3000 miles. At 100,000 miles you would have change your oil 34 times. Your oil change cost 25.00 dollars you would have spent 850.00 dollars. At 15,000 miles a year it would have taken you 6.7 years to obtain 100,000 miles. At 850.00 dollars divided by 6.7 years equals 126.87 dollars a year. If your car is over 6.7 years old and you have to put a new engine or rebuild, will it total the car? I will change my oil every 3,000 miles and let the oil change centers make their money on my oil changes instead of my engine repair. Seems cheap to me to spend 127.00 dollars a year on depreciating asset to keep it running.
      • 8 Months Ago
      My 1987 Ford Ranger, V6 engine, has a bit over 350,000 miles on it. Changed oil (Mobil 1 Synth) once a year on my birthday. I did however, at 4000 miles service the truck. That is add fluids, rotate and check air to tires, lube etc. BUT LET ME CLEAR THAT I DID NOT RECOMMEND THIS OTHERS LIKE MY SISTER IN LAW. SHE NEVER CHECKS HER OWN OIL AND I HAVE HAD TO STOP HER FROM DRIVING ON A FLAT TIRE THAT SHE DID NOT NOTICE. SHE NEEDS SOMEONE TO CHECK HER CAR OUT AT 3000 MILES. SHE MIGHT AS WELL GET THE OIL CHANGED.
      • 8 Months Ago
      We just traded our 1997Ford Exployer in and it had 289,0000 miles on it. I changed the oil on it around every 7,000 miles. It was a very good vehicle for us.
      • 8 Months Ago
      The easiest thing to do on a car is change your oil. Do it every 3-5k especially if you have a lead foot and like to bring up the RPMs. I am the owner of an 87 full size blazer with 200k on it. Only thing that went wrong mechanically is a distributor and an EGR valve. P.S. - Mobile 1 rocks
      • 8 Months Ago
      Jon Kite
      • 8 Months Ago
      Changing oil at 3,000 miles only deplets our supply and puts mor $$$$'s in the oil co's pockets. I have a 1989 Nissan Maxima with 7000,000 miles on it. I kept the first engine until 417,000 an the second now has 327,000 and I only changed oil @ 7,000 miles + filter. You who are wasting your $ on more frequent oil changes....STOP IT !!! Your wasting oil too. Jon Kite
      • 8 Months Ago
      These are all good personal stories but I think the author missed with you need to ask the dealer service dept. what type of oil is used in the vehicle. When it says 7500 between changes it's more than likely the manufacturer is using synthetic oil. I wouldn't trust regular oil for that long under any conditions. And the best reason for I like for syn oil is in the cold weather they start and run so much better.
      Hello Steegs
      • 8 Months Ago
      I change every 3,000 miles or 3 month's, I believe oil gets dirty, and it's not hard to change, the hard part ,is trying to find someone to recycle your old oil & filters.
      • 8 Months Ago
      im not sure how the shops are in the rest of the world but in erie pai have not found one shop that i trust. lets start off when i was 16 an my first truck was an 88 f150 i had the starter fall out so i took it to a shop to replace it all went well untill acouple days later it fell out again i took it back there 3 times same thing happend obviously not paying for the other times but still i got sick of it and did it myself an it never fell off since since after that i had tranny problems so i took it to a supposably respectable shop the problem was with the front seal so they recommended replacing the whole tranny which now a relize was over kill. so then i move to an eagle talon, one inspection said that i needed a new ball joint having it being still under warranty i took it to the dodge dealership they replaced the wrong ball joint twice and the third time i went out and it wasnt replaced i told the shop mannager to give me a lift an 20 mins ill change it myself. and another example with monroe, i sold a car to this girl having looked over it myself and i know what goes into an inspection which the car would have no problem passing so she comes back all pissed off because her car didnt pass well as soon as she pulled in i knew something wasnt right someone took a drill and drill holes through the whole exaust fresh drill holes no rust or anything i dont even leave my car for inspection if a mechanic is working on my car im in the shop with them or there not doing the work well onto this oil stuff i currently have an 87 toyota supra and it was in pretty ruff shape to say the least i only paid 200 dollars for it, now this has the oil monitoring system on it and i noticed ******** not accurate to say the ************** to change every 10,000 miles and if u go by that u when it says to change the oil if u just rest it then it will just count down from 10000 again i dunno if a sensor or something in it is bad wouldnt surprise me with all the sensors they are putting on cars now,i go by the color of the oil an it has always worked out to be about 5000 miles or 6 months which for an engine with 178 k on it thats doin pretty good its kinda funny the most reliable car i have ever had is the one i paid 200 dollars for an fixed myself and thats anywhere from new brakes to the head gasket i changed the first thing everyone should do when they buy a car is go out an buy a repair manual for it alot of problems with cars can be fixed pretty easy with a repair manual and alittle common sense depending on the vechicle, has anyone else noticed that car companys are deliberatly making it harder for the back yard mechanic to work on his car, newer cars if u dont have a diagnosis machine then your pretty well ****** and there are alot more special tools now that u would not need back then and its been like this for awhile u go back to the 60s an 70s and any idiot with a set of tools an half a brain could take the car apart and put it back together, oh an for these guys that actually feel the need to tell somone it takes more gas at 70 then at 55mph on the highway it all depends on the car my car gets better gas milage at 70 then it does at 55 it all depends on the gearing every car as a sweet spot where u will get the best gas mileage go faster an your engine has to work harder go slower and and your gas mileage will go up for example if your cars sweet spot is 55 and u do 40 it will take u longer to do a mile an u would also probably be in a lower gear which will give u worse gas milage point is that every car is differerent and everyone would benifit from knowing there car before they start driving it or even buy it
      John Thomsen
      • 8 Months Ago
      Oil is relatively cheap, new or rebuilt engines aren't! I try to change the oil AND filter every 3,000 miles and I have never had any major engine repairs in 50 years of driving-and most of my cars ended up with well over 100,000 miles when I sold them. A friend of mine maintained the family taxi fleet and he got over 345,000 miles without any major engine work on a 64 Chevy before the engine had to be repaced. Frequent oil changes are cheap insurance if you intend to keep your car (and your money)
      • 8 Months Ago
      I work at a shop and we have a policy to treat customers the way we want to be treated. We don't upsell you repairs or install used parts in place of new and then bill you for new like someone else said shops do. We advice you what repairs are needed and what can wait. That has worked for us for many years and will continue long after I'm dead and gone. If your reapir bill seems to be high all the time go somewhere else and get another opinion, you don't need to fix it there. Some shops do operate like that and I've told my customers or others who have come in for a second opinion. The small mom and pops shop are your best bet. The big franchise shops operate on high revenue and need it to stay in buisness, thats how they pay for those fancy shops. Do your home work and you can find a reputable shop in your area. As far as oil changes and service, all depends on how you drive and how new you vehicle is. I recommend 3000 miles for oil changes doing mostly intown driving and 5000 miles highway driving. 50,000 for belts and hoses and 100,000 for timing belts.
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