Which do you think is better:
Royal Purple synthetic or Amsoil synthetic? Why?
Just rejoined the world of the connected after several months underway; sorry I'm catching this one late.
When I lost an LS6 motor in my first season of SCCA racing (while running Mobil 1 15w50), I did several months of research on oils trying to determine if there was a better oil that might have helped prevent my engine failure. I primarly was looking at Royal Purple and Redline.
What I discovered, contrary to Route 66's statement above, is that oils, both dino and synthetic, are vastly different, in both their basestock and their additives. These differences contribute to differences in performance.
The API classifies oils into five different groups.
Group I base oils are the least refined of all of the groups. They are usually a mix of different hydrocarbon chains with little or no uniformity. While some automotive oils use these stocks, they are generally used in less demanding applications.
Group II base oils are common in mineral based motor oils. They have fair to good performance in the areas of volatility, oxidation stability, wear prevention and flash/fire points. They have only fair performance in areas such as pour point and cold crank viscosity. Group II base stocks are what the majority of engine oils are made from. 3000 mile oil changes are the norm.
Group III base oils are subjected to the highest level of refining of all the mineral oil stocks. Although not chemically engineered, they offer improved performance in a wide range of areas as well as good molecular uniformity and stability. By definition they are considered a synthesized material and can be used in the production of synthetic and semi-synthetic lubricants. Group III is used in the vast majority of full synthetics or synthetic blends. They are superior to group I and II oils but still have limitations. Some formulations are designed for extended oil changes. AMSOIL XL Motor Oils
, Castrol Syntec and many others fall into this category.
Group IV are polyalphaolefins (PAO) which are a chemically engineered synthesized basestocks. PAOs offer excellent stability, molecular uniformity and performance over a wide range of lubricating properties. AMSOIL SAE Synthetic Motor Oils
and Mobil 1 primarily use group IV basestocks. PAO is a much more expensive basestock than the highly refined petroleum oil basestock of Group III.
Group V base oils are also chemically engineered stocks that do not fall into any of the categories previously mentioned. Typical examples of group V stocks are Esters, polyglycols and silicone. Redline uses an ester basestock.
In the 90s, Mobil filed suit against Castrol for falsely advertising Syntec oil as synthetic, when in fact it contained a Group III, highly hydroprocessed mineral (Dino) oil, instead of a chemically synthesized (group IV or V) basestock. Due to the amount that the mineral oil had been chemically changed, the judge decided in Castrol's favor. As a result, any oil containing this highly hydroprocessed mineral (Dino) oil (currently called Group III basestock by the American Petroleum Institute) can be marketed as a synthetic oil. Since the original synthetic basestock (polyalphaolefin or PAO) is much more expensive than the Group III basestock, most of the oil blenders switched to the Group III basestock, which significantly increased their profit margins.
When I was trying to decide between Royal Purple and Redline, I discovered AMSOIL. What impressed me about AMSOIL was that it used the same basestock as the stock Mobil 1 (Group IV PAO basestock), but used oil analysis reports showed AMSOIL used higher levels of detergents and anti-wear additives. This was somewhat confirmed when Mobil 1 came out with their Extended Performance Mobil 1. When Mobil 1 came out with this new product, at the time they claimed that it had about 50% more detergent and anti-wear additives than the regular Mobil 1.
What turned me off to Royal Purple were several poor used oil analysis reports I reviewed, and the fact that they did not say on their website what type of basestock they used. Other companies such as Redline, Mobil 1, and AMSOIL were very up front with their basestock, so I wondered what Royal Purple was trying to hide.
My research indicated to me that Redline was (and still is) a very good oil, but I was somewhat concerned that its basestock was Group V, an ester basestock, and I'd read a few bad reports on the ester's effects on seals in the Corvette transmission.
As I'm now an AMSOIL dealer, I obviously chose to go with AMSOIL. Since I switched to AMSOIL in 2004, I have had no transmission or differential failures in my Z06, nor have I had any oil related engine failures (I did lose an engine due to a failed timing chain and another when the harmonic balancer came off).
Since then AMSOIL has included Royal Purple in a few oil comparisions.
There is a four-ball wear test on this page of my dealer website:
AMSOIL Series 2000 20w50
And Royal Purple was included in this extensive motorcycle oil comparison:
AMSOIL Motorcycle Oil “White Paper”
(1 MB pdf file)