What is the best synthetic motor oil?

Synthetic motor oils are becoming more and more popular. By now, most people know that synthetic oil far outperforms conventional oil.

Just a few years ago, there were only a handful of synthetic motor oils available. But now, there are over a dozen that most DIY garage mechanics can choose from. Once you've decided that a synthetic oil is the better choice for your car, the obvious question is "Which one is the best?".

Every TV commercial for synthetic motor oil says theirs is the best. Most of the time, however, they offer vague reasons why. Often they don't offer any real proof at all, relying on fluffy slogans such as "Nothing outperforms Mobil 1" or "It's liguid engineering".

To get a true gauge of which one is the best, you really need to look at actual scientific tests performed on all of the oils. And not just one test, but several tests that test the different important functions that a motor oil needs to provide. That's what we offer here on this page. Look at ALL the test results, and then judge for yourself.

The following ASTM industry standardized test were performed on ten different synthetic oils in February 2013. All of the motor oils were obtained in November and December of 2012. The tests were conducted by a third party independent lab. The oils were coded to eliminate bias, meaning that the technicians did not know which oils were which.

• Four-ball wear test (ASTM D 4172 Mod)
• Total base number (ASTM D 2896)
• Cold cranking viscosity (ASTM D 5293)
• Thermo-oxidation engine oil simulation test (ASTM D 6335)
• NOACK volatility test (ASTM D 5800)

Here are the 5W-30 synthetic motor oils that were tested:

• AMSOIL Signature Series Synthetic Motor Oil
• Castrol Edge with Titanium Fluid Strength Technology
• Lucas Synthetic
• Mobil 1 Extended Performance
• Pennzoil Ultra
• Petro-Canada Supreme Synthetic
• Quaker State Ultimate Durability
• Red Line High Performance Motor Oil
• Royal Purple High Performance Motor Oil
• Valvoline SynPower Full Synthetic Motor Oil

Four ball wear test

A motor oil's most important job is to prevent the wear of your engines metal parts that are constantly rubbing together.

Three stationary ball bearings are submerged in the oil in a triangle pattern, with a fourth ball bearing sitting on top of them. The top ball is spun on top of the three lower balls while a heavy load is applied. After a set period of time, the test is stopped and the wear scar on the three balls is measured and averaged.

The smaller the wear scar, the better the wear protection.

AMSOIL Signature Series has always shined in this test, and these latest results are no exception. No other synthetic oil protects against wear better than AMSOIL. The top 4 oils all had wear scars under 0.40 mm. Notice that Mobil 1 showed the largest wear scar by far.

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Total base number

Total Base Number (TBN) is the measure of a motor oil's reserve alkalinity, which controls acids formed during combustion. TBN can also be used as a measure of an oil's degradation in service. Motor oils that have a high TBN and demonstrate good TBN retention are known to effectively reduce the corrosive effects of acids over time.

AMSOIL Signature Series has the highest TBN, two points higher than the next competitor. This is one reason why AMSOIL Signature Series excels in providing protection over extended oil drain periods.

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Cold cranking viscosity

The Cold Crank Simulator Test determines the apparent viscosity of lubricants at low temperatures and high shear rates. Viscosity of lubricants under these conditions is directly related to low-temperature engine cranking. The test was performed at -30ºC (-22ºF). Results are reported in centipoise (cP), with lower values reflecting easier cold starts and reduced battery strain. To meet the API SN and ILSAC GF-5 motor oil specifications, a motor oil’s cold crank viscosity must not exceed 6,600 cP.

There was a large difference between viscosities measured. AMSOIL Signature Series exhibited the lowest cold cranking viscosity.

Thermo-Oxidation Engine Oil Simulation Test

Motor oils can form deposits when exposed to increased heat, reducing efficiency and contributing to poor overall performance. According to the ASTM, the TEOST test method “is designed to predict the high temperature deposit forming tendencies of an engine oil. This test method can be used to screen oil samples or as a quality assurance tool.”

Given the number of vehicles now equipped with direct fuel injection, turbochargers and other performance-enhancing technologies that increase heat, deposit control has taken on increased importance. To meet the API SN Resource Conserving and ILSAC GF-5 motor oil specifications, a 5W-30 motor oil must limit total deposit formation to 30 mg or less.

Results demonstrate a range of performance differences between oils. Only Castrol Edge with Titanium Fluid Strength Technology and AMSOIL Signature Series Synthetic Motor Oil limited total deposit weight to 5 mg or less.

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NOACK Volatility Test

The NOACK Volatility Test determines the evaporation loss of lubricants in high-temperature service. According to the ASTM, “Evaporation may contribute to oil consumption in an engine and can lead to a change in the properties of an oil.”1 As with the TEOST test, low values in the NOACK Volatility Test are of particular benefit in modern, hot-running engines.

In the NOACK test, a candidate oil is exposed to heat and circulating air. Following 60 minutes, the remaining oil volume is weighed and compared to the original weight, with the difference reported as the percentage of weight lost. Results must be limited to 15 percent or less to meet the API SN and ILSAC GF-5 specifications.

While all oils were below the API SN and ILSAC GF-5 upper limit, results indicate differences in hightemperature volatility. Half of the oils limited the percentage weight lost from volatility to under 10 percent, with AMSOIL Signature Series Synthetic Motor Oil having the third-best result.

Overall conclusion

AMSOIL Signature Series performed the best in 3 of the 5 tests, and performed well in the remaining two. None of the other synthetic motor oils showed such good results. Some perform well in one or two tests, but not very well in the others.

Also, ask yourself what other motor oil brand publishes so many tests of their product versus their competitors. Most just spend lots of money on expensive TV commercials and catchy slogans. For 40 years now, AMSOIL has produced the best synthetic motor oil on the planet.

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The full document of the testing is available here.