AMSOIL vs. Royal Purple vs. Mobil 1 In Comparison Testing

A heavyweight battle between three perennial motor oil  favorites.

AMSOIL, Royal Purple and Mobil 1 have been long considered to be top-end motor oil brands. A recent independent, standardized lab test was conducted to determine how well each brand could combat deposit formation. Here are the contenders.

• AMSOIL Signature Series 5W-30 Synthetic Motor Oil
• Royal Purple API 5W-30 Synthetic Motor Oil
• Mobil 1 Extended Performance 5W-30 Synthetic Motor Oil

About The Test

The TEOST 33C test (also known as “ASTM D6335”) is a laboratory test apparatus that replicates the operating conditions of a turbo-charged engine. Engine oil is circulated through the machine at fluctuating temperatures between 200°C and 480°C for two hours. Moist air and nitrous oxide is added to the oil. This duplicates internal engine conditions. The weight of the carbon deposits created during the test determines the result.

Note the test results on your left. AMSOIL Signature Series 5W-30 Synthetic Motor Oil generated just 7.0 mg of deposits. Royal Purple API 5W-30 ended with 25.4 mg and Mobil 1 Extended Performance 5W-30 created a whopping 28.2 mg of carbon deposits. The API SN and ILSAC GF-5 motor oil industry standards dictate a TEOST 33C limit of 30 mg. As a result, Royal Purple and Mobil 1 barely make the grade in the deposit test. AMSOIL Signature Series 5W-30 delivers a spectacular result.

Why Is Deposit Control Important?

Engine deposit control has always been vital, but never more important than today. Today’s car buyer expects maximum fuel economy and reasonable horsepower output. The solution for many car makers is the turbocharger. Turbochargers spin at upwards of 250,000 revolutions per minute and can create exhaust gas temperatures in the 1000°C range. Using an engine oil that can withstand these rigors is paramount. Even very tiny carbon particles in the engine oil can eventually wreak havoc on expensive turbocharger bearings.

AMSOIL Signature Series 5W-30 Synthetic Motor Oil delivers 3 to 4 times the deposit fighting power of the high-end offerings from Mobil 1 and Royal Purple. Imagine how budget-priced engine oils might perform in this test? If you have a turbo-charged engine, do not cheap out on motor oil. An ultra-high quality motor oil like AMSOIL Signature Series could be the best preventative measure money can buy. Expect the same turbo performance from Signature Series 0W-20, 5W-20, 10W-30, 0W-40 and 5W-50.

Not All Synthetic Oils Are Equal

Even the (supposedly) top-end Mobil 1 Extended Life and Royal Purple synthetic oils performed dismally in this common, standardized deposit test. You get what you pay for and AMSOIL consistently delivers.