Motor Oil Myths and Facts

Summary

1. Don't fall for the 3000 mile myth or the dark oil myth

2. Follow the manufacturer's recommended change interval for severe service or have an oil analysis performed to see if you can use the normal service interval

3. If you do the oil changes yourself then buy the oil and filters near the date of the oil change and keep a maintenance log with receipts

4. Use an API certified 5W30 or 10W30 oil (whatever your manual says is preferred) and watch out for oil change places that force 10W30 on you

5. Don't use oil additives

6. If you really want to know the optimum time to change your oil than have oil analyses performed

7. Use the manufacturer filter or a quality after-market filter (don't go by brand name recognition!)

8. Synthetic oil is a good choice if you have a high performance engine or if you live in an extremely cold climate, otherwise it provides no benefit (but no harm either).

9. Avoid engine flushes

10. Check your oil

Introduction

I created this web site because wanted to dispel some of the misconceptions about motor oil, oil change intervals, and filters. I've been advising people about oil changes on Usenet for years and I felt it would be easier to have a central repository of all my wisdom to refer people to. One of the main purposes of this site is to dispel the age old myth about 3000 mile oil changes. This myth is being perpetrated by both the oil change industry (i.e. Jiffy Lube) as well as by well meaning, but misinformed, individuals.

History

As internal combustion engines for passenger vehicles have been forced to become more fuel efficient, less polluting, smaller, and longer lasting, their lubrication needs have changed dramatically. These changes in the engines have required the development of multi-weight detergent motor oils that are suitable for the tighter clearances, higher heat, and higher RPM of these engines. These oils have additives to reduce wear (especially at start-up), maintain viscosity, and to suspend the soot and contaminants (by-products of combustion) that they wash off the interior engine parts. A side benefit of these oil's ability to maintain viscosity and suspend soot is that the oil change intervals have become longer on most vehicles.

Sludge

The number one reason for oil changes is to prevent the formation of sludge. It's important to understand how sludge forms and how sludge formation is prevented.

How Sludge is Prevented
Additive in the detergent oils 'wash' any contaminant particles off of internal engine parts and hold these particles in suspension until the oil is changed. It's important to understand that these particles are too small to cause engine wear, but they do turn the oil a darker color. The key thing is to change the oil before the oil becomes too saturated with contaminants to hold any more, but color is not an indication of this condition.

How Sludge Forms
As explained above, modern detergent oils suspend contaminants so they do not settle on engine parts and form sludge. When the oil becomes saturated with contaminant particles new particles settle out of the oil onto the internal engine parts and form sludge. This is why it is so critical to perform oil changes before this level of contamination is reached. The only way to know if you're oil needs changing is to have an oil analysis done. Absent this, play it safe and follow the severe service interval specified in the owners manual. Remember that the contaminants come from the combustion process of the gasoline and and the air. Synthetic oil will not prevent these contaminants. Synthetics may be marginally better at suspending more contaminant particles, but not enough to prolong oil changes by much.

Never attempt to clean the inside of your engine with one of those engine flush procedures that many shops try to sell. If you've been diligent about oil changes there will be no sludge. If there is a lot of sludge then the last thing you want to do is to dislodge it all at once.

Oil Change Intervals

Few subjects generate as much debate on Usenet as the proper oil change interval. Since few people bother with oil analysis the debate centers on time and mileage.

Follow the Money
Unfortunately, there are market forces that have a vested interest in convincing vehicle owners to change their oil more often than necessary. The legal prey of these market forces have become convinced that they are purchasing "cheap insurance" or "peace of mind" by changing their oil more often than necessary. Complicating things is the fact that doing oil changes is one of the few do-it-yourself maintenance tasks that is still within the ability of the backyard mechanic to perform.

Recreational Oil Changing
The term "recreational oil changer" was coined to define people that change their oil far more than necessary because they actually enjoy doing it. It's easy to understand the psychology behind the recreational oil changing. It's the visceral feel of the tools, the victory when that old oil filter breaks free, the hot dirty oil pouring out, the joy of oiling of the gasket on the new filter, that new copper or fiber gasket on the drain plug, the clean clear oil going in, and the sense of accomplishment when you start the car, the oil light comes on for a moment, then goes out. For $8-10 in oil and parts, it's pretty cheap entertainment, but if people would be content to do it only when it provides some benefit to the vehicle it would be better.

The 3000 Mile Myth
The 3000 mile oil change interval has been pounded into people's heads for decades. It had a scientific basis when engines used non-multi-weight, non-detergent oil. It no longer has any scientific basis, but it is still being promoted by certain entities, most notably the oil change industry in the United States. This myth is also sometimes known as the "Cheap Insurance Myth."

The 3000 Mile Fact
There are still vehicles that need 3K oil changes, but it's not because the oil goes bad after 3K miles. One example is the Saturn S series. These vehicles have a timing chain system that is very sensitive to clean oil because oil pressure is used as hydraulic fluid to ratchet up the timing chain tensioner. If varnish forms in the timing chain tensioner bore then this system can fail and the chain will become loose and eventually break. Dealers have gone as far as tearing out the normal service schedule (6000 miles) and leaving only the severe service schedule. If your engine is destroyed (under warranty) by a failed timing chain then the dealer will legitimately request evidence of oil changes. Unfortunately this problem usually won't manifest itself during the warranty period.

The Dark Oil Myth
Dark oil does not indicate the need for an oil change. The way modern detergent motor oil works is that minute particles of soot are suspended in the oil. These minute particles pose no danger to your engine, but they cause the oil to darken. A non-detergent oil would stay clearer than a detergent oil because all the soot would be left on the internal engine parts and would create sludge. If you never changed your oil, eventually the oil would no longer be able to suspend any more particles in the oil and sludge would form. Fortunately, by following the manufacturer's recommended oil change interval, you are changing your oil long before the oil has become saturated. Remember, a good oil should get dirty as it does it's work cleaning out the engine. The dispersant should stop all the gunk from depositing in the oil pan.

The only real way to determine whether oil is truly in need of changing is to have an oil analysis performed. Since most people don't want to bother with this, it's acceptable to err heavily on the safe side and simply follow the manufacturer's recommended change interval for severe service. There are still a few cars that specify 3K intervals for severe service, but not many. If you look at countries other than the U.S., the oil recommended change interval is much higher than even the normal interval specified by vehicle manufacturers in the U.S.

Severe Service versus Normal Service
Each manufacturer specifies what constitutes normal and severe service. Generally, severe service consists of operating the vehicle in a very muddy or dusty areas (because dust particles get through the air filter and contaminate the oil more quickly), operating the vehicle in a very hot areas (heat breaks down oil more quickly), using the vehicle only for short trips in cold weather (the moisture in the oil never gets vaporized), or using the vehicle for towing or when carrying a car-top carrier. You'll often see claims such as "everyone falls into the severe service category," but these claims are untrue (follow the money and see who's making these claims). If you primarily do freeway driving in moderate weather you do not fall into the severe service category. If you're in doubt, the best way to see if you fall into the severe service category is to have an oil analysis done at the mileage of the severe service interval. Many people just like to play it safe and follow the severe service schedule, which is fine, but there is no benefit in changing the oil sooner than the severe service schedule states.

Maintenance Schedules Vary by Country
Different countries have different maintenance schedules, even for the same car. This fact has been the cause of long argument threads on Usenet. How could the exact same car need a different service schedule simply because of where the vehicle is used? At least part of the reason is due to the differences in fuel. For example, the U.S. and Canada has fuel with high sulphur levels which can cause more oil contamination. Japanese fuel has very low sulphur levels. Europe is in-between. Some of the newer engine technology (direct injection) which raises fuel economy, requires low sulphur fuel. Of course the oil companies have a vested interest in not lowering the sulphur as it adds to refining cost and enables more fuel efficient engines. Since "Big Oil" is in bed with the un-elected president in the U.S., don't expect any action of lower sulphur fuel for a while in the United States. If Al Gore is re-elected in 2004, and the Supremes don't simply ignore the election results again, then there is a chance for lower sulphur fuel in the U.S. beginning in 2005.

Oil change intervals with synthetic oil
Synthetic oils withstand higher temperatures before breaking down, and have more base stock and less viscosity modifiers. Synthetics wear out, become acidic, and eventually become saturated with suspended soot particles, just like regular oil. Again, an oil analysis is a good investment to determine the optimum oil change interval. Never exceed the manufacturer requirements for normal service.

Filter Change Interval
Back in the days of 3000 mile oil changes many manufacturers recommended filter changes only half as often because the filter did not become clogged with dirt at only 3000 miles. This was good advice back then, especially because with non-detergent motor oils a lot of the sludge remained stuck to internal engine parts rather than being carried in the oil to the filter. Nowadays the filter should be changed at every oil change. There are some people who believe so much in synthetic oil that they change filters without changing the oil. There's no harm in changing the filter without changing the oil, but there is no point in doing this.

Do-it-yourself versus paying someone to do it
Oil changes are pretty inexpensive when done at a reputable repair shop or dealer. Most dealers offer oil change specials that cost less than the quick-change oil places, and the dealers do a better job and use better filters. Where I live the dealers have very long service department hours including on Saturday (some on Sunday). The dealers also offer a time guarantee, generally that they'll get you in and out in less than 30 minutes or the next oil change is on them. Another advantage of having it done at a repair shop or dealer is that you have solid legal proof of the date and mileage when the oil change took place. My personal preference is to have the oil changed at a dealer during the warranty period. Edmunds has a page on secret warranties that states: "If you service your vehicle through an independent or aftermarket facility, what does the manufacturer owe you in terms of assistance? Manufacturers cannot control the quality of the parts used or work performed when you service your vehicle through aftermarket service facilities. Also remember that the treatment you receive as a customer has a great deal to do with you being a loyal customer to the dealer and the manufacturer."

If you change the oil yourself follow these guidelines (especially during the warranty period):

1. Buy the oil, filter (from the dealer), and drain plug gasket (if necessary) within a few days of the oil change (don't stock up during a sale). You want dated proof that you bought the supplies near the date of the oil change.

2. Keep a log book of your maintenance. Staple the receipts for the oil and filter into the book.

3. If you really want to be anal then take a dated photograph of the oil change being performed. Have the photos processed at a lab that dates the back of the prints. Stick the prints into the maintenance log.

None of this really proves that you changed the oil when you said you did, but it would be sufficient should the manufacturer challenge a warranty claim based on lack of oil changes.

Quick-Lube (and dealer) Problems to Watch Out For

1. SAE30 oil. Some quick-lube places have been known to offer advertised specials that use SAE 30 oil, as opposed to 5W30 or 10W30. Pay the extra for the proper oil, or better yet avoid merchants that try to pull this kind of thing because it's an indicator that they are less than honest.

2. Trying to use the wrong oil because it's what they have in bulk. Insist on the oil that is specified on your filler cap and in your manual.

3. Pumping the oil out through the dipstick hole instead of removing the drain plug. I came across this gem when I asked if I needed to bring my own copper drain plug gasket. They said that they didn't remove the drain plug to drain the old oil. This was the Oil Changer location at Kifer & Wolfe in Sunnyvale, California. Pumping the oil out through the dipstick hole is a terrible way to get the old oil out because it leaves a lot of junk in the bottom of the oil pan. This was a long time ago and maybe they've changed their ways since then.

4. Selling unneeded and overpriced services such as engine flushes.

5. Selling overpriced, and often low quality, parts such as wiper blades and washer fluid, PCV valves, thermostats, etc. Never let a quick-lube place do any mechanical work on your vehicle.. They do no use journeyman mechanics.

6. Using poor quality filters. You really want to bring your own filter, from the dealer, with you when you go to a quick-lube place. They may take $1 or $2 off the price if you do this but don't count on it.

7. If you have a vehicle that actually still has Zerk fittings to lubricate then be sure that they actually lubricate these fitting. Most cars no longer require lubrication but some trucks still do.

8. Do not let a quick-lube place change or add any fluids other than oil. No transmission fluid, no brake fluid, no power steering fluid, no antifreeze, no oil additives, no fuel additives. It is just too easy for them to use the wrong fluid and cause permanent damage to your vehicle.

Which Oil to Use

Detergent Oil
Virtually all modern multi-weight oils are detergent oils. Detergent oil, cleans the soot of the internal engine parts and suspends the soot particles in the oil. The particles are too small to be trapped by the oil filter and stay in the oil until you change it. These particles are what makes the oil turn darker. These tiny particles do not harm your engine. When the oil becomes saturated with soot particles and is unable to suspend any more, the particles remain on the engine parts. Fortunately, with the current oil change intervals the oil is changed long before the oil is saturated.

Non-detergent oil, such as SAE 30, is not used in modern passenger vehicle engines. It is still used in some gasoline engines such as lawnmowers.

Oil Viscosity
The viscosity of multi-weight motor oil is specified using two numbers. The first number is the viscosity when the oil is cold. This is followed by the letter W (which stands for winter, not weight), which is followed by the number that indicates the viscosity when the oil is at operating temperature. The higher the number the thicker the oil.

Viscosity Modifiers
In order to protect an engine at start time, the oil needs to be thinner when cold so it flows freely. Viscosity modifiers are added to the base stock to make the oil flow better when cold, without making the oil too thin when hot.

Climate Considerations
Owner's manuals and service manuals will specify the acceptable oil to use at various temperatures. In warm climates, 10W30 is usually an acceptable alternative to the preferred 5W30 and may be used without measurable adverse effects. In the olden days, before multi-weight oils, it was common to have a winter oil and a summer oil. This is no longer necessary, but if you normally use 10W30 because you live in a warm climate then be sure to switch to 5W30 if you plan on using the vehicle in very cold weather.

5W30 versus 10W30
Virtually all new passenger vehicles sold in the U.S. use either 5W30 or 10W30 oil. The difference between the two is that the 5W30 flows better when cold, so if you live in a cold climate or operate your vehicle in a cold climate during the winter months, you should use 5W30 if it is the preferred oil for your vehicle. If you live in a sub-tropical climate and don't operate your vehicle in cold climates, then 10W30 is acceptable as long as the manufacturer specifies that it is permissible to use it.

Is there a disadvantage to using an oil that flows better when cold, i.e. 5W30 versus 10W30?
Sometimes, but usually not. The crux of the issue is this: the bigger the difference between the cold oil viscosity and the hot oil viscosity, the more the volume of viscosity modifiers and the less the volume of base stock. If you are good about following the manufacturer's recommended oil change interval then stick with the 5W30 if that is the preferred oil for your vehicle, even if 10W30 is acceptable in warmer climates. Older cars may specify 10W30 only. This is because they need a little more viscosity when cold to keep a protective film on the cylinder walls. There have been instances where the larger amount of viscosity modifiers that are present in 5W30 have broken down due to excessive heat and have left carbon deposits on the valves, but this is extremely rare. The proper fix would be to reduce the excessive heat, but the workaround was to use an oil with less viscosity modifiers.

Why do many oil change places, even dealerships, use 10W30 instead of 5W30, even when 5W30 is preferred?
According to www.cartalk.com (see link in the references section), as well as many mechanics who have posted on usenet, 10W30 is the closest thing to a one size fits all oil. Many older vehicles need 10W30, and most newer vehicles are okay with it in warmer climates. Since many garages don't want to have multiple tanks of bulk oil they choose to carry only 10W30. The advice that Tom & Ray give is correct, 'it would not be a disaster if you used 10W30, but given a choice, go with the manufacturer's recommendation and use the 5W30.'

Thicker is Better Myth
The reason that oil viscosities have gotten thinner is because bearing clearances have become smaller. Using thicker oils will interfere with oil flow and the oil pressure will increase. In a worn engine it may be okay to increase the viscosity of the oil because the bearing clearances have become larger.

Oil Additives
Do not use any oil additives no matter how much they are hyped on TV. They provide no benefit and can interfere and react with the additives already present in the oil. Some additives have particles that can clog oil passages and clog filters. Common additives that are heavily hyped are Slick 50, Duralube, and Prolong.

Oil Analysis
To determine the optimum oil change frequency for your vehicle requires that you perform several oil analysis during one oil change interval. For example, if your vehicle has 15,000 miles on it and the manufacturer recommends 7500 mile oil changes for normal service and 5000 miles for severe, perform an analysis at 18,750 miles, 20,000 miles, and 22,500 miles (if the first or second test shows a need for an oil change then stop there). Do not exceed the manufacturer's normal service interval even if the analysis shows no need for an oil change at 7500 miles. The oil change industry desperately desires that you NOT perform such an analysis. The almost certain result for most drivers will be that even at 7500 miles the oil will still be fine.

Even after your vehicle is out of warranty it is a good idea to continue to follow the manufacturer's schedule for maintenance. There are frequently special campaigns (not recalls) to fix latent defects after the warranty has expired. Lately we've seen these on some Toyota V6 engines and some Saturn engines. You want the manufacturer to have no excuse to deny coverage. Also you can sometimes get a manufacturer to share the cost of an expensive repair when something fails after the warranty has expired, but this is at their pleasure and it is best to have solid proof that you have followed the maintenance schedules.

Big oil users like bus companies and truck fleets use oil analysis to extend the life of their engines without unnecessary oil changes. The reasons are clear. These big engines can use 3-4 gallons of oil and unnecessary changes are expensive in both time and materials. In some cases they change the filters and put in additives to replace the acid neutralizers and anti-wear agents. A good analogy is swimming pool maintenance. You clean the filters, you remove the debris, you add stabilizers and disinfectants, but you rarely empty the whole pool and refill it.

Filters

Regular Replacement Filters

Manufacturer Filters
This is usually the best choice for your vehicle.

Aftermarket Filters
These are filters made by companies like Fram,Wix, Motorcraft, Lee, AC/Delco, Bosch, Casite, Hastings, Pennzoil, Valvoline, and Purolator. The quality of these filters varies greatly. In many cases the auto manufacturer uses these filters themselves. Private label filters are made by these companies as well.

Trade Brand Filters
These are filters made for the oil change industry. They are actually no worse than the poorer quality aftermarket filters. You can't buy these at an auto parts store but you'll see them used at many of the quick oil change places.

Premium Filters
Some manufacturers of synthetic oil also make so-called synthetic filters. These are high priced and have not been proven to provide any benefit over a high quality manufacturer of aftermarket unit.

Bypass Filters
Bypass filters have been used on diesel truck engines for years. On cars they are a messy solution to a non-problem. Forget it.

Synthetic Oil

Advantages of Synthetic
Synthetic oil was originally developed for high performance racing engines. Mobil tried to popularize synthetic oil for passenger vehicles back in the early 1970's. At the time, Mobil was promoting 20K or 25K oil changes with synthetic, but they soon backed down from this. Synthetic oil is a good choice if you have a vehicle with a high performance engine (in fact synthetic is required for many of these engines). It is also a good choice if your vehicle is operated in extremely cold climates. It has higher resistance to breakdown caused by heat and it flows better in extreme cold. Unfortunately for the synthetic oil industry there is virtually no advantage to using synthetic oil in a non-high performance engine that is operated in moderate climates. You probably could go a bit longer between oil changes with a synthetic, i.e. following the normal service schedule even if you fall into the severe service category, but I wouldn't advise this. In short, synthetic may give you the peace of mind of knowing that you are using an oil that is far better than necessary for your vehicle, but it won't reduce wear or extend the life of the engine. The mistake some people make it to wrongly extrapolate these benefits onto normal engines operated in mild climates, with the ultimate lack of any knowledge being manifested with statements such as "synthetics provide 'Peace of Mind,' or 'Cheap Insurance,'" or other such nonsense.

Extended Change Intervals
Most manufacturers of synthetic oil advise users to not exceed the manufacturer's recommended oil change interval. Part of this is self interest (they don't want to be liable for any damage) but the real reason is that synthetic oil, while it does have certain advantages, still becomes contaminated.

Be extremely wary of synthetic oil companies that offer to pay for your repairs if it is determined that their oil and their extended change interval recommendation caused the problem. Think for a moment of the incredible hassle you would have to go through to prove responsibility for an engine problem. Who would pay your legal bills? Who would pay for replacement transportation during the battle? The more bizarre the warranty the poorer the product is a good rule of thumb.

API Certification, Phosphorus & ZDDP
Never use a non-API certified synthetic oil (there are many of these on the market). The problem with the non-API certified synthetics is that they contain too much phosphorus (in the form of the additive ZDDP (Zinc Dialkyl Dithiophosphates)). The API has limited the amount of phosphorus because phosphorus shortens the life of the catalytic converter. These oils are fine for snowmobiles, motorcycles, and older cars that don't have a catalytic converter, and the extra ZDDP does provide additional wear protection. Unfortunately, the marketers of some the non-certified oils do not explicitly and honestly state the reason for the lack of API certification. You can check the status of API certification on the API web site. Be certain to go not just by the manufacturer name but by the actual product as well. This is because a manufacturer will sometimes have both certified and non-certified products. Suffice it to say that Mobil 1, Royal Purple, Castrol, & Havoline all make synthetic oils that are API certified and that can be purchased at auto parts stores and other retail outlets. Amsoil has one product line, XL-7500 that is API certified, but it's other lines contain too much ZDDP to be certified and should not be used in vehicles with catalytic converters.

Amsoil
Amsoil actually makes some very good products. The negative image of Amsoil is due to their distribution method (MLM) and their marketing approach. If Amsoil products were competitively priced with Mobil 1 and other synthetics, and if I could buy them in a store, I would not hesitate to use their XL-7500 synthetic as opposed to Mobil 1. What upsets me about Amsoil is that they didn't disclose until recently (and then it was by accident) the real reason that their oils (except for XL-7500) are not API certified. In the past they came up with all sorts of bizarre excuses about the reason for their lack of API certification and this greatly contributed to the distrust that people have of the company.

Engine Flushes--The Latest Scam
Engine flushes pump heated solvent through your engine, supposedly to wash away sludge. But regular oil changes with detergent oil already take care of the sludge problem. And if you actually have an engine that is full of sludge the last thing you want to do is do an engine flush because the sludge can clog the oil passages and destroy the engine completely. These flushes are completely unnecessary. All they do is wash the money out of your wallet. As Click and Clack state: "This is what's known in the business as a "profit center." Something the garage can use to beef up the amount each person spends per visit. So unless you've got a very old car, and are trying to solve a specific, sludge- or carbon-related-problem, I'd skip the R-2000." These engine flushes usually sell for about $130. The victims are people that think that they are doing something nice for their vehicle by cleaning the engine. In fact a dealer or repair shop that tries to sell you an engine flush should be avoided for all service because they are untrustworthy.

Check Your Oil
Check your oil level at least every other fill-up. It's easy to become complacent about this, especially because few modern vehicles burn much oil. However there are still a few vehicles that have serious oil burning problems and owners have wrecked their engines by running out of oil.

Toyota Sludge

Toyota has instituted a service program for owners that have experienced sludge. Toyota claims that this problem occurs as a result of not following the scheduled maintenance, but clearly Toyota would have no obligation to do anything at all if this were indeed the case. Apparently the problem is a result of owner's who qualify for severe service following the regular service schedule. Toyota has three different sets of criteria for deciding whether or not you qualify for severe or normal service and this caused confusion.