Larry Crider
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Today’s engines are smaller, lighter and produce more horsepower per cubic inch than ever before and yet hold less oil volume, stressing the engines oil to the maximum.    

Horsepower increasing additions such as turbo charging and super charging have become common place. Add in ever stricter emissions controls with the stop and go commuting common in today’s congested cities and you have operating conditions that are torturous for your cars motor oil.     

So what qualities does motor oil need to have to be able to survive these conditions and still provide proper protection? As they say, “the devil really is in the details” when it comes to a properly formulated motor oil.   

We’ll start with issues dealing with viscosity. Good motor oil must be able to maintain a constant viscosity when exposed to temperature changes. It is also very important that the oil be able to maintain its proper viscosity for the entire duration of its intended drain interval.   

A motor oils pour point tells you how well it handles cold temperatures without gelling (solidifying). Oils that contain too much paraffin; a wax found in petroleum motor oils tend to gel at low temperatures. Oils with poorly designed additives or low quality viscosity index improvers will also have this problem.  Modern engines have tight tolerances’ and need an engine oil to flow quickly at low temperatures to minimize wear at start up.   

Tip: Look for oils that have low pour points.The Pour Point Test determines the lowest temperature at which a lubricant flows. The lower a lubricant’s pour point, the better protection it provides in low-temperature service.   

At high temperatures and pressures, motor oil must be able to resist shearing forces. The condition known as shear is where the oil is literally torn apart on the molecular level causing it to drop out of its proper viscosity range (example: a 40wt oil shearing into the 30wt range)   

This brings us to the subject of volatility and heat related deterioration. At high temperature an oils lighter components can volatilize and boil off. This is especially true of petroleum based motor oils which have a mix of hydrocarbon molecules of various sizes. At high temperatures, the lighter parts boil off leaving the heavier parts. This causes a gradual increase in viscosity and leads to accelerated wear, sludge and engine deposits. The ability to resist shear and volatilizing is particularly important in turbocharged applications where the oil passes through the turbochargers scorching hot bearings.     

Full synthetic motor oils made from polyalphaolifin- a manmade engineered molecule, have a uniform molecular structure that is far less volatile at high temperatures making them ideal for high temp/ turbo charged applications.   

Volatility is measured using an industry test called the NOACK volatility test and is measure in percentage of weight lost. Good oils will offer 10% or less loss on this test. Synthetic engine oils will often be less than 8 % loss with some lower than 5%.   

Tip: Shear stability testing is done using the ASTM high temperature/high shear stability test (ASTM HT/HS test). Look for oils that do well on this test   

Tip: Look for oils with higher flash/fire points. The Flash/Fire Point determines the lowest temperatures at which application of a flame will cause lubricant vapors to ignite (flash point and sustain burning for five seconds (fire point). Lubricants with higher flash and fire points tend to exhibit more stable volatility characteristics.   

Wear control is that one big thing that people usually consider the most when choosing a particular motor oil to purchase.   

A motor oils first line of defense against wear is its initial viscosity. Like any other liquid, oil is not compressible. Having the oils film between two moving parts in and of itself prevents wear. Under increasing load though, at some point the oils film will fail allowing metal to metal contact and wear. This is known as a “boundary lubrication” situation. (Note: synthetic oils offer a film strength averaging ten times higher than typical petroleum oils)   

To prevent contact between moving surfaces under these condition, Motor oils contain anti-wear additives such as zinc, phosphorus and calcium. These act to form a sacrificial layer that prevents metal to metal contact.   

Higher quality motor oils usually have higher treat levels of these anti-wear additives. It must be noted though that merely having large amounts of these ingredients does not guarantee better wear protection. The quality of the anti-wear additives is of equal importance.   

A motor oils anti-wear performance is tested using the ASTM 4 ball wear test. 3 steel balls are submerged in the oil to be tested and a 4th ball is rotated against them at a given temperature and pressure for 1 hour. At the end of the hour the 4 steel balls are removed from the test apparatus. The scars on the balls where they were in contact are measured and averaged. The smaller the size of the wear scars the better the oils wear fighting ability   

Tip: Look for motor oil that performs well on the ASTM 4 ball wear test. Wear scars smaller than .055 inch is very good. Wear scars .045 inch or less are exceptional. Wear scars less than .040 inches are outstanding. Note: Many oil companies do not publish the results of the ASTM 4 ball wear testing for their oil although a few do, most notably; Amsoil Inc. which publishes full test results for all its products.   

The next thing to consider is the motor oils ability to control acid formation and maintain engine cleanliness.   

A motor oils acid fighting ability is expressed as TBN or total base number. The TBN number is a measurement of the motor oils reserve alkalinity. As the miles go by and the hours of use on the oil add up this number will generally come down, meaning the acid fighting ability is becoming depleted.    

Motor oils designed to be used for OEM drain intervals will commonly have a TBN in the 7.5 to 8.3 range. Synthetic motor oils offering drain intervals in excess of 10,000 miles will often have TBN’s of 8.5 to 9. Very high grade synthetic motor oils like Amsoil long drain; designed for up to 25,000 miles or one year have a TBN number greater than 9 giving them tremendous long term acid fighting ability.   

Besides controlling acid build up, quality motor oils contain detergent and dispersant additives to control contaminants in the oil. The detergent additives keep deposits, sludge and varnish from forming and sticking to engine surfaces and dispersants keep these contaminates in-capsulated and suspended so the engines oil filter can effectively remove them.    

Other parts of the motor oils additive package are there to prevent such things as rust and corrosion from both combustion byproducts and moisture and to keep the oil from foaming under the churning parts inside the engine. Foam control is very important because oil that has a tendency to foam will have lowered film strength and can even cause cavitations to the engines oil pump and loss of oil pressure leading to increased wear.   

Tip: Even if the motor oil packaging says it meets your car manufactures specifications, inexpensive, lower quality motor oils usually have lower treat levels and use lower quality additives that become depleted more rapidly during use. This leads to an engine that is dirtier, has more deposits and shows more wear over time than the same engine would be running higher quality motor oil.      

The best oil is one that offers exceptional wear protection, has a wide operational temperature range and is shear and oxidation stabile. It should also have a high degree of detergency to keep things clean and great acid fighting ability.   

Does that sound like too much to ask? Frankly, the biggest challenge for any oil manufacturer is to produce a balanced product. While it is relatively simple to design a motor oil that performs extremely well on one particular test, say the ASTM 4 ball wear test, it takes far more expertise and expense to make an oil that performs well across the board. Experience counts when formulating motor oil!   

So as you can see modern engines demand a lot from their oil and choosing really high quality motor oil makes a big difference in the long run.   

Think about this. You had no control over how your car was designed. No control over the quality of the metal used to build it. No control over the workmanship of the people who assembled it, but the quality of the oil, lubricants and filters you put into your vehicle is the one thing you have absolute control over!   

Choosing the highest quality motor oil you can find that meets your car manufactures’ requirements is the one sure way to maximize the life of your engine and get the most from your automotive investment.   

Amsoil Inc introduced the first fully synthetic motor oil to meet American Petroleum Institute requirements in 1972. Today Amsoil is considered the world leader in synthetic motor oils and lubricants.  

By Larry Crider, lubrication specialist