Originally Posted by homeslice

AMSOIL Signature Series 0W-30 Severe Service is the very best and is a 35,000 mile/1-year oil. Change the AMSOIL EAO oil filter every 25,000 miles/1-year. If you do not put 35,000 miles per year on then the 5W-30 (ASL) or the 10W-30 (ATM) are also excellent choices and both are 25,000 mile/1-year lubricants. All AMSOIL Synthetic Lubricants meet and far exceed all manufacturer specifications as well as API Specifications.

The AMSOIL Signature Series 0W-30 Severe Service is a racing oil and of a different chemistry than the 10W-30 and 5W-30. They often use the 0W-30 in the 800 Hp Ford/Roush Nascars as it has a shear strength better than most 50W oils and transfers heat more efficiently than heavier oils. Only about 60% of the engine cooling is done by the coolant and the rest is done by the oil via heat transfer. The 10W-30 and 5W-30 would not be good choices for racing. The 5W-30 ASL product code and 10W-30 ATM are both 25,000 mile/1-year oils where the 0W-30 is a 35,000 mile/1-year oil. The 4-ball wear test is also run at a different load, temp and RPM than the other 2 products so they cannot be compared in that area. The 0W-30 does not thin out to a 0W as it gets hot. It stays a 30W just like the 10W-30 and the 5W-30. They are ALL 30 weight oils and each one can be beneficial in a specific application. The 10W-30 is a better oil under certain instances for higher mileage engines as it has a lower volatility.