As an AMSOIL Direct Dealer (and forum vendor), I'm clearly biased, but I went through the same thought process in late 2003 after losing a motor (LS6) in my first season of running my relatively stock 2002 Corvette Z06 in the SCCA T1 class.
I originally sought to compare Royal Purple and Red Line vs Mobil 1. I discovered AMSOIL in the process and chose it over the others. I started using it, was happy with the results and started selling about halfway through 2004. Been using it in all my vehicles since.
Here's what I learned. Feel free to take this with a grain of salt.
All synthetics are not equal. The API has not come out and defined what is "synthetic", but rather, classified oils into five major 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 (though recent info posted on the oil forum indicates that Mobil 1 is also now using a significant proportion of Group III basestock). 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. Red Line 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. Interesting that Mobil 1 may now have gone the way of most other synthetic oil manufacturers.
AMSOIL clearly indicates that their XL line is Group III and the rest of their synthetics are Group IV. Red Line clearly states that they use a Group V, Polyol Ester, basestock. Royal Purple doesn't state what they use. Mobil 1 now doesn't state what they use either. I'd ask why not and wonder if they are both using a large amount of Group III basestock.
Next consideration is additives. I reviewed hundreds of used oil analysis reports on the oil forums and came to my own conclusion that AMSOIL uses higher levels of anti-wear and detergent additives. The result is a clear improvement in wear numbers in the used oil analysis reports I reviewed.
I next considered High Temp High Shear rating. The High Temperature/High Shear Test measures a lubricant’s viscosity under severe high temperature and shear conditions that are similar to severe service applications in an engine. The below HTHS ratings were pulled straight of the corporate websites of the various companies.
Amsoil Signature Series 0w30 (API SM) – 3.2 (meets GM Standard 4718M)
Amsoil SAE 10w30 (API SM) – 3.2 (meets GM Standard 4718M)
Amsoil SAE 5w30 (API SM) – 3.2 (meets GM Standard 4718M)
Amsoil XL 5w30 (API SM) – 3.2 (meets GM Standard 4718M)
Amsoil XL 10w30 (API SM) – 3.2 (meets GM Standard 4718M)
Amsoil XL 5w30 (API SM) – 3.2 (meets GM Standard 4718M)
Pennzoil Platinum 10w30 (API SM) – 3.15 (meets GM Standard 4718M)
Mobil 1 10w30 (API SM) – 3.14 (meets GM Standard 4718M)
Mobil 1 EP 10w30 (API SM) – 3.1
Mobil 1 EP 5w30 (API SM) – 3.1
Pennzoil Platinum 5w30 (API SM) – 3.1 (meets GM Standard 4718M)
Pennzoil Truck/SUV 10w30 (API SM) – 3.1
Mobil 1 5w30 (API SM) – 3.09 (meets GM Standard 4718M)
Mobil 1 Truck/SUV 5w30 (API SM) – 3.09
Pennzoil Truck/SUV 5w30 (API SM) – 3.0
Mobil 1 0w30 (API SM) – 2.99 (meets GM Standard 4718M)
Amsoil SAE 0w20 (API SM) – 2.8
Amsoil XL 5w20 (API SM) – 2.7
Mobil 1 EP 5w20 (API SM) – 2.7
Mobil 1 5w20 (API SM) – 2.62
Mobil 1 0w20 (API SM) – 2.61
Pennzoil Platinum 5w20 (API SM) – 2.6
Pennzoil Truck/SUV 5w30 (API SM) – 2.6
Pennzoil Platinum 0w20 (API SM) – 2.6
I did not list Red Line's HTHS rating as they use a different ASTM method and I'm not sure direct comparison is valid, but their numbers are good. I did not list Royal Purple's HTHS ratings because they don't report them. Again, made me uneasy as to why not.
Finally, AMSOIL has done some very comprehensive motorcycle oil and gear lube tests and Royal Purple did not fair well at all - their oils tend to shear out of grade fairly quickly. The full reports if you are interested:
AMSOIL Motorcycle Oil “White Paper” (1 MB pdf file)
AMSOIL Gear Lube “White Paper” (2 MB pdf file)
Here is an example of how AMSOIL's best oil performs in my 06 CTS-V:
Cadillac CTS-V Used Oil Analysis – Mobil 1 5w30 vs AMSOIL 0w30
I'd offer you more info on the
AMSOIL Preferred Customer Program which allows purchase at dealer wholesale pricing, about 25% under retail., but I see your location as Italy and unfortunately, I can't sell outside the United States and Canada. Sorry.
One day after Preakness and the familiar cry rings from the Clubhouse once again: ".....and they're offfff !!!"
Somehow I knew this would happen...
