Last time we focused on the stuff from which lube oil is made. This time we'll focus on arming you with the information you need to make a good oil selection.
 |
| A sample of a viscosity chart that covers various temperatures for multigrade oils. The actual values for the grades shown may vary from manufacturer to manufacturer. The colored arrows along the temperature line show the approximate lower end temps for single grade oils. |
You can learn the basics from the oil container. From there, the internet is the place to go for detail. The oil companies' websites are treasure troves of useful info. Some list more than others on the Material Data Sheets (MDS) but a call or e-mail to their tech hotlines with a specific question will often yield more info if you need it. There's also a website called BITOG (see sources below), which is a clearing house for oil enthusiasts to debate and share knowledge.
Knowing what the specs mean will help you make a better selection. They are generally based on ASTM (American Society for Testing and Materials) procedures. Some tests offer a more accurate picture than others but the important part is to compare the results of the same tests.
Viscosity (V): In a MDS, they are listed in cSt (at 40C and 100C) or SUS (100F and 210F).
Viscosity Index (VI): This is a good indicator of the oil's viscosity changes over a wide range of temperatures. A high number is better and indicates one of two variables; lots of VII (Viscosity Index Improvers) additives, or its a synthetic base oil, or both. Initial performance will be good either way, but the highly additive-enriched oil will begin to degrade sooner than will a oil with a naturally high VI. There are also better and worse VII, so a higher quality oil will hold up better. Multigrade oils have a higher VI than single grades and synthetics are higher than mineral (generally).
Flash Point (FP): The flash point is obtained by heating the oil until it begins to vaporize. The listed number is the lowest temperature at which the vapor will ignite. The higher this number is the better. Low flash point oils tend to be consumed faster as they vaporize inside a hot engine. The minimum acceptable spec for new oil is about 400F. You like to see it around 420 in mineral oils and 450 in synthetics. Fuel dilution significantly degrades the flash point in used oil.
NOACK Volatility: Another test that will indicate the potential for evaporative losses of a oil (oil burning). A lower NOACK number indicates an oil with a low potential for evaporative losses.
TBN: Total Base Number. This indicates the oil's resistance to forming acids. Gas rated oils start off around 6-7. Diesel rated oils have more detergents and start off around 10-12. In general, you would look for the higher TBN, In the long run, the initial number isn't as important as how fast the number drops. Depending on the quality of the ingredients, the TBN may drop very quickly or slowly. You cannot determine this without oil analysis. The additive levels are dangerously low at about 2-3, as read from oil analysis.
HTHS: High Temperature High Shear. Not often seen but a good indicator of a oil's resistance to shearing and losing viscosity. The specification varies by SAE grade and is rated at a specific temperature. In general, the number gets higher with viscosity, but higher than the minimum for any viscosity means the oil is more resistant to shear. Synthetics often test higher than mineral oils within their grade. The minimum with most SAE 30 and 40 gas engine oils is about 2.9 cP. For diesel rated oils of SAE 40 and above, 3.7 cP is the minimum. Any oil that is above 4 cP is getting good, the higher the better within the grade.
Pour Point: The minimum temperature at which the oil will pour. Below the pour point, the oil is like ice cream. At the pour point, it's more like honey, so the usable point where the oil will circulate well is always much higher than the pour point. Pour point is more a useful spec for gear oils. Pour Point Improvers can be added to the oil to make it more fluid at low temps.
CCS: Cold Cranking Simulator: also known as Low Temperature Pumping Viscosity. This rating is a more useful way to rate the cold temperature performance of an oil. The spec applies to the winter grade part of the oil. Different grades have a different minimum spec and are rated at different temperatures. 0W rated oils are measured at -35C, 5W at -30C, 10W at -25C, 15W at -20C and 20W at -15C. In general, when comparing the number at a given temp, the lower number indicates better cold flow.
4-Ball Wear Test/4-Ball EP Test: These are two similar tests that start the same. The wear test measures the scarring on four ball bearings, one spinning and rubbing against the other three, when subjected to test loads in the lube being tested. The least depth of the scar shows the best performance. You sometimes see the 4-Ball Test applied to motor oils, but it's unusual. More common is the EP test, which is seen in gear oil specs and measures the force required in kilograms per square inch to weld those bearings together. This "test-to-the-death" is often used to rate gear oils and the highest load attained before welding shows the best oil.
Brand on the Bottle
We can break the oil biz down into three basic categories, the big oil companies like Chevron/Texaco, Shell, etc.; the boutique blenders like Amsoil, Lubrication Engineers, Royal Purple, Redline, Schaeffers, etc.; and the independent blenders that bottle for various entities like Wal-Mart, Meijers, Tractor Supply and so on. In general, you should have no fear of any of these oils.
The basic credo is, "You get what you pay for." Every manufacturer has a variety of oils in a variety of price ranges. Beyond finding a close-out sale, you aren't generally going to get the best base oil and additive package at dollar store prices, but it pays to shop.
The major oil company brands are consistently a good value in any category of oil. Because they bottle millions of gallons of oil, they can offer a very good oil for the price. They also have the big R&D departments that have come up with many of the major advances in oil technology.
The so called boutique blenders offer the "fine wine" of the oil industry. They produce in smaller amounts, but offer top notch formulations using what they each think are the best-of-the-best combinations of base oils and additives... some of them pretty whiz-bang formulations. The prices reflect the product.
Finally, there are a number oil companies whose names you almost never hear or see. They bid on contracts to produce oil under various other brand names for retailers, such as grocery and department stores, dollar stores and auto parts stores. These can be stellar or less-than-stellar oil, depending on what the contract specifies. Some are excellent, some are fair at best.
Picking a Good Oil
Beyond the really cheap no-name oil, most oil can be used with good effect. The cheaper stuff just needs to be changed more often and herein lies one of the problems. Too frequent oil changes are wasteful of resources. In some cases, good oil is being dumped. There is NO benefit to changing the oil more often than it needs to be. A better oil lasts longer in service than a bottom dollar oil and that can save you money, especially if you shop well, as well as preserve resources.
Your selection should be based on the four criteria below. Your choice would be a blend of these four criteria. Where they conflict, you must let the most important and common factors dictate the choice.
Manufacturer's Requirements: In the motor oil area, not many car and truck makers require anything super special, even if they try to steer you one way or another. Mainly their requirements concern viscosity and API service rating, but if the manufacturer makes a special requirement, it's best considered. Automatic transmission fluid, manual transmission oil and power steering fluid are three places where you may see some specific requirements that should be heeded. Some of the boutique blenders offer superior products to replace these special oils. If in doubt, the first step is to check the bottle. If it says something like "Suitable For" instead of "Meets or Exceeds" then that is strike one against the product. The final word on this is that a major variance away from a specific requirement should only be made after careful consideration... including possible future warranty claims.
Driving Conditions: This criteria is closely related to the service interval. Your choice of viscosity would fall under this heading. If you drive in a very hot climate or do a lot of towing and lugging, you need a higher viscosity oil (tempered by cold climate considerations, see the sample viscosity chart nearby). If you drive in mostly colder or cooler climates, the opposite is true. An engine that spends a lot of time under load at low rpms needs a higher viscosity than one run at a higher rpm. An engine that runs consistent oil temperatures over about 212 degrees also may need more viscosity. With regards to axle and gear oil, the same general rules apply. A truck that hauls or tows heavy loads can benefit from higher viscosity oil. Ditto if the truck is operated in hot conditions.
 |
| An inexpensive oil filter with few pleats and very little media. |
Climate: As discussed above, when the temps go up, so should the viscosity. The reverse is true for cold climates. This applies to engine and gears oils but not often to ATF or manual light transmission oils. A truck in the hottest parts of Texas, for example, might be best with an SAE 40 oil, where a truck in the cool Pacific Northwest would be fine with an SAE 30 and a truck in Alaska might be OK with an SAE 20, even if all three share a similar driving cycle. It's all specified in the owner's manual. The winter part of a multigrade oil offers the most climate flexibility.
 |
| Better quality filter with a lot more media. |
You will have noticed that we didn't get into these divisions much. With the improvements in mineral oils these days, the term "synthetic" has become as much marketing as a technical division. Instead of using this division as your single criteria, balance the performance of a oil against the use you intend and then look at the price. Few of us operate on a "cost-is-no-object" basis. In many cases, a good mineral oil will greatly exceed the need. Don't forget the term "synthetic" could mean a Group III mineral base oil, a Group IV PAO or Group V ester synthetic base.
Blended oil mixes a percentage of synthetic into a mineral oil base (usually a Group II+). This does tend to enhance the performance of the oil, but the amount of synthetic added can be as little as 10 percent. The prices are usually more than 10 percent higher than a fully mineral based oil, so you may not be getting performance that equates to price.
Where you need to focus on the base oil is at the performance extremes. Climate is one such extreme, heat or cold, but especially cold. Extended oil drains are another area where a synthetic makes a lot of sense. The lubrication quality of a synthetic, especially a PAO or ester base, is higher than a mineral oil, so there is often a fraction more power or economy to be had from a synthetic. These gains are real, but typically small.
Where synthetics make the most sense for everyone is in axles. No oil filter, high temperatures, shock loads, hypoid action... all contribute to working the oil very hard. Add in the incredible heat stresses of towing and the shock loads of 'wheeling, and the need is even greater.
A good synthetic will reduce axle oil temps by reducing friction. A temp reduction of 30-35 degrees is not unusual going from an ordinary mineral oil to a syn. Because synthetics offer such great cold flow characteristics, a heaver oil can be used. Often an SAE 110 (a new designation not yet seen everywhere) and SAE 140 synthetic can be used even in areas of cold weather. The more viscous oil offers better shock load protection in a 'wheeling rig than a SAE 90. The problem is that unless the axle spends a lot of time really hot, the heavier oil can cost fuel economy due to fluid friction. The nice part of a synthetic SAE 140 is that due to the superior friction characteristics of the base oil, there isn't as much parasitical drag as there would be with a mineral SAE 140.
 |
| A cutaway of a K&N filter shows some quality elements. This filter is not equipped with a bypass valve but many are. Note that K&N has since gone to synthetic media and increased filtering capability. |
The best engine oil is of only minimal use without the means to filter it. Wear metals and carbon from combustion are two internal sources. Dirt and dust from the outside can find it's way in, typically through the air filter, where it coats the cylinder walls and is washed off by oil splash. These particles are tiny but many of them are big enough to do damage and they need to be removed as soon as possible.
It's commonly stated that particles from 10 to 20 microns (0.001-inch = 25.4 microns... a human hair is about 70 microns) are the most common and damaging size in the short term. Ten micron filtration has more or less become the industry standard, but some premium filters can capture smaller particles. Particles from 5-10 microns are less immediately a problem but are a long term wear issue.
With internal engine clearances in the 30-40 micron range, it's easy to predict particles that large will be a problem, even accounting for a good hydrodynamic layer. We also know that the hydrodynamic layer lessens or completely fails at times, so anything caught between the two surfaces will have a wearing effect
Modern lubrication systems use full-flow filters, meaning all the oil is filtered. Therein lies the quandary. Oil filtration is a balance of filtering ability, flow rate and holding capacity. The engine needs a certain amount of oil flow. The finer the filtration is, the less the flow. You can compensate for this by increasing the amount of filtering media, but there are obvious space limitations. Filter media that captures smaller particles tends to clog faster as well, so flow ability is reduced as that happens.
Upgrades in filter media have begun to offer finer filtration while maintaining flow and adequate capacity. Any time you see the terms, "synthetic media," listed for a particular filter, it's worth a look as most of them will outperform the more common pressed cellulose media. Also, some aftermarket companies offer bypass filter kits. These will have very fine filters that take a small portion (10 percent or so) of the pressurized oil to filter as small as 1 micron
fvHow can you tell a good filter from a so-so one? There are several criteria. The higher end filter manufacturers are fairly open with specifications but virtually all will respond with most specs via calls or e-mails. Here are some of the more common specifications.
Nominal Micron Rating: The least useful rating that indicates the filter can capture at least 50 percent of the particles at the size listed. Also seen simply as, "Micron Rating."
Absolute Micron Rating: A useful rating meaning the filter will capture at least 98.7 percent of the particles at the size listed.
Beta Ratio: A very useful rating when you understand it. This is a multi pass-rating that counts the number and size of a specific mix of particles that can get through the filter over a specific period of time, under specific pressures and at specific temps and various fluid viscosities. The particle size tested may vary, but the ratios reflect the percentage of particles that get through.
Example: A K&N 6001 filter has the following Beta Ratio Specs:
10/20/30=2.1/21.7/1000
10/20/30 are the micron sizes of the particles tested.
2.1/21.7/1000 are the Beta Ratios for those particles.
To get the percentages from the Beta number, subtract 1 from the Beta number and divide by the Beta number and multiply by 100. Our 2.1 would then be: 2.1-1= 1.1/2.1= 0523 x 100= 52.3 percent. Because our numbers are rounded, we did not quite reach K&N's published Beta Ratios of 53.1 percent at 10 microns (20 micron= 95.4 percent and 30 micron = 99.9 percent). For quick reference, here are common Beta Ratios and corresponding efficiencies.
Beta Efficiency
2 50%
10 90%
20 95%
75 98.7%
100 99%
200 99.5%
1000 99.9%
Flow Rate: Commonly seen in gallons per minute (GPM) or liters per minute (LPM). This is the filter's ability to flow oil in a clean state. As the filter captures particles, its flow rate goes down.
Capacity: The amount of material the filter can capture before there is a significant pressure drop across the two sides of the filter. The drop is typically 8 psi. and is often measured in grams.
Design elements play a part in a quality filter. Some of these will be reflected in the performance specs, but most can only be seen in a filter "autopsy."
 |
| What happens when the oil gives up the ghost in an axle? This! Step One: The oil gets so hot and thins so much that the hydrodynamic barrier is lost. Step Two: The heat increases so much that the EP additives are cooked away. Step Three: Metal-to-metal contact, rapid wear and total failure. |
Bypass Valve: Many engines have an internal bypass valve that will allow unfiltered oil to flow past the filter in the event it plugs. Engines that do not have one built in require a valve in the filter. Some are merely a flapper type valve and better ones have a coil spring backed valve.
Canister and Endplate: Beyond the burst pressure specification, canister durability is of some importance to 'wheelers if a rock or debris goes up and whacks at the filter. Burst pressure usually only plays a big part in racecars, but a higher number is an indicator of a robust filter. The endplate design may indicate durability and the size and number of holes may indicate flow rate.
 |
| Cam lobes on flat tappet cams often go bad due to lubrication problems. The most recent API classification for gas engines, SM, is a bit light on the anti-wear additives needed by older flat-tappet engines, namely zinc and phosphorus. This is especially important when breaking in a new cam. There are cam break-in additives, or you can run a diesel rated oil, which still has higher levels of these two additives. |
Sources
BITOG (Bob is the Oil Guy)
www.theoildrop.server101.com
K&N Engineering
www.K&Nfilters.com
Royal Purple
www.royalpurple.com
