AMSOIL Signature Series 100% Synthetic 5W-30 Motor OilAMSOIL periodically publishes testing of their synthetic motor oils and sometimes they push the limits of conventional test methods, just to prove a point. The time they ran their synthetic 20W-50 in a Harley-Davidson in dyno testing until the engine temperature reached over 500°F comes to mind.

This time around, their Signature Series Synthetic 5W-30 was subjected to independent testing, but with a bit of a twist. The testing method was the ASTM “D7320 Sequence IIIG Engine Oil Test” which is used as a vital part of the process for engine oils to meet the API SN and ILSAC GF-5 specifications. It evaluates a motor oil’s ability to maintain viscosity, resist consumption, prevent deposits and control wear. AMSOIL changed things up by doubling the testing interval. In other words, they ran the same batch of 5W-30 oil through two complete test trials.

How the Testing Was Conducted

Using a GM 3800 V-6 engine as the test bed, the independent lab ran the engine through 100 hour test interval with a steady engine oil temperature of 150°C. In regular automotive applications, engine oil temperatures typically run at approximately 90°C.

After the 100 hour test, the engine was disassembled and measurements for camshaft and lifter wear, carbon deposits and engine oil viscosity were conducted. The engine was then reassembled using the same parts and the same batch of engine oil was reinstalled. The test was then rerun for another 100 hours under the exact same parameters.

The Results

Signature Series 5W-30 barely broke a sweat in the 100 hour trial and still aced requirements of the API SN and ILSAC GF-5 specifications by a mile after 200 hours.

Piston Deposits

A minimum grade for the API SN and ILSAC GF-5 specifications for piston deposits in the Sequence IIIG Engine Oil Test is a rating of 4. A score of 5.5 after 100 hours is regarded as excellent. In the 100 hour trial, AMSOIL Signature Series 5W-30 earned an excellent rating of 7.70. After 200 hours, the same batch of oil still attained a remarkable rating of 7.42. You’ll note in the photos below, the pistons are ultra-clean after the grueling 200 hour test. This is a testament to the AMSOIL Signature Series’ resistance to sludge, varnish and carbon deposits.

Pistons After 200 Hours of Testing With AMSOIL

After 200 hours of high temperature testing using AMSOIL Signature Series, you could eat off of these pistons.

Heavy Piston Deposits Using a Competing Engine Oil

A competing motor fails the piston deposit portion of the Sequence IIIG Engine Oil Test after 100 hours.

Piston Ring Deposits

The API SN and ILSAC GF-5 specification requires that there can be no stuck piston rings after the 100 hour Sequence IIIG Engine Oil Test. This category of the test also addresses an engine oil’s ability to fight carbon deposits under hot operating conditions. After both the 100 and 200 hour tests, there were no stuck piston rings in the AMSOIL 5W-30 test.

Camshaft and Lift Wear Testing

In order for an engine oil to qualify for the API SN and ILSAC GF-5 specs, an oil must meet minimum cam and lifter wear thresholds in the Sequence IIIG Engine Oil Test. The minimum amount of wear is 60 microns. After 100 hours, the cam and lifter wear was a scant 14.8 microns with AMSOIL Signature Series 5W-30. The same cam and lifters were installed in the engine and another 100 hours was logged in testing. The total wear after 200 hours was just 17.6 microns.

Camshaft Shows Little Wear After Synthetic Oil Testing

Valve Lifters After Engine Oil Testing

AMSOIL Signature Series 5w-30 achieved remarkably low cam and lifter wear after 200 hours of the Sequence IIIG Engine Oil Test.

Viscosity Test Results

During high-temperature operation, engine oils have a tendency to thicken. This can lead to deposits, poor performance and compromised wear protection. In the 100 Hour Sequence IIIG Engine Oil Test, a viscosity increase of 50% is considered a very good result. The passing grade for the API SN and ILSAC GF-5 specifications is a 150% increase in viscosity. After 100 hours AMSOIL Signature Series 5W-30 had a viscosity increase of 27.6%. After 200 hours of testing, this viscosity increase was just 41.5%. A viscosity increase of 41.5% is considered outstanding after the 100 hour test, so AMSOIL’s performance after 200 hours is nothing short of spectacular.


We know of no other oil company that has publicly put their motor oil through a second helping of the 100 Hour Sequence IIIG Engine Oil Test. AMSOIL’s willingness to push the envelope with their products has always impressed us. The Signature Series Synthetic Oil formula proves itself to be stable under high temperatures and highly resistant to wear. This is the case in both testing and in the real-world conditions of your engine.