AMSOIL VS Royal Purple and Mobil 1 Extended Performance: Deposit Protection


In 1985 I worked with my father to replace the heads and make other repairs needed to put a 1972 Fiat Sport Spider back on the road. The experience taught me why, in many circles, FIAT stands for, “Fix It Again Tony.” At 17, when I eventually got to drive the car, I experienced firsthand the pride and excitement enthusiasts have in their personalized statements of horsepower and style. I also found out why enthusiasts pay so much attention to every detail about their vehicle, including the level of protection motor oil delivers.

Turbocharger demands on motor oil

Advancements in automotive technology have since driven advancements in motor oil chemistry and have complicated the process of evaluating oil. Due in large part to the ability to offer power and fuel economy, turbochargers have become one of – if not the most – widely used advancements in performance technology. The following are just a sample of turbocharged 2016 makes and models:

  • Volkswagen GTI
  • Buick Regal
  • Subaru WRX
  • Ford Fiesta
  • BMW 3 Series
  • Ford Mustang EcoBoost
  • Ford F-150 EcoBoost

When exposed to increased heat, motor oils can form deposits, reducing efficiency and contributing to poor overall performance. Given the

Turbo Glows Red Hot
File photo of extreme conditions, not part of the TEOST 33C test (ASTM D6335) test. Used for illustrative purposes only.

number of vehicles on the road now equipped with turbochargers and other performance-enhancing technologies that increase heat, such as direct injection and variable valve timing , deposit control has taken on increased importance.

AMSOIL goes head-to-head with Royal Purple and Mobil 1

Among auto enthusiasts, three brands often dominate the conversation about motor oil protection: AMSOIL, Royal Purple and Mobil 1. Each has a history of providing solid protection. Yet, wherever enthusiasts gather, be it in online forums or car shows, when the topic of serious motor oil protection is discussed the debate often turns to which brand offers more protection. Recently, AMSOIL enlisted an independent, third-party lab to compare the three brands in an industry-standard test that focuses on protecting turbochargers.

Independent test measures turbo deposits

The TEOST 33C test is an American Society for Testing and Materials (ASTM) bench test that simulates turbocharger operating conditions and, according to the ASTM, the test method “is designed to predict the high temperature deposit forming tendencies of an engine oil.” To meet the API SN Resource Conserving and ILSAC GF-5 motor oil specifications that are often recommended by vehicle manufacturers, a 5W-30 motor oil must limit total deposit formation to 30 mg or less.

The following graph shows the test results from the independent, third-party lab. This industry-standard test shows AMSOIL Signature Series 5W-30 Synthetic Motor Oil prevents deposits 4X better than Mobil1® Extended Performance and 3.6X better than Royal Purple®.

Turbo Protection AMSOIL Vs Royal Purple & Mobil 1

The results show AMSOIL Signature Series 5W-30 held deposits to well under the 30 mg limit recommended by vehicle manufacturers. Test results represent the formulations as they were available to consumers in April 2016. Formulations were coded to eliminate bias during testing, and samples were tested in random order. An appropriate number of trials of each oil were run to produce results at or above the 95 percent confidence level when compared to AMSOIL Signature Series 5W-30 Synthetic Motor Oil.

Hopefully this information adds a few more data points to the discussion when enthusiasts and people that care about what they drive compare notes on three of the leading brands that offer serious protection for the cars and trucks they take pride and passion in.



  1. Check most Advance auto Parts stores for some products and if they don’t have it they can get it. Or better yet open a Preferred Customer account to buy direct from Amsoil. Show me a brand that test to be better than Amsoil. Amsoil is best in 9 out of 10 tests.

  2. I’m thinking of switching over from T6 to this. I have a 2016 wrx and modifies and car calls for 5/30 but tuner tells me 5/40. I’m not an oil guru but if the car calls for a 30 why put a 40 in it. I know 30 is for fuel economy but thinking that there are tight tolerances in engines now wondering why you wanna put a heavier oil in the motor??? I’m ready to pull the trigger on it just trying to decide on the 30 or 40. Any input is greatly appreciated

    1. Hi Kirk. You could become a preferred customer and order direct. If you have any questions about the process please contact me.

    2. Hello Kirk,
      Thank you for the comment. You’re right; AMSOIL is not widely distributed at national auto parts store chains. However, by visiting you can find a source that fits your needs. At you can purchase all AMSOIL products online, or find an AMSOIL Dealer or independent retailer near you that carries AMSOIL. Distributing our products through these outlets enables us to avoid making trade-offs that may compromise our goal of engineering products that offer enthusiasts more protection and performance.

  3. I use AmSoil Sig 5W-50 Syn (hard grade to find w no zinc additives in it) in my NON Turbo ’13 Mustang Boss 302 and its performance is AWESOME!
    And that’s 9 qts.
    Wouldn’t use anything else if you paid me!

    1. Thank you for the invitation. However, our time and resources limit the scope of the brands we test and at this time we won’t be including additional brands for this test.

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