JohnBrowning, You are very biased against the Northstar engine, that has been made very apparent in our past discussions. The things that I am telling you here have been said by a GM engineer, they could never be from my own experience as you well know. The reason GM says that 0W-40 anything is bad for the Northstar is specifically due to the large amount of VII improvers needed in conventional dino oil to get that wide of a viscosity range. 10W-30 was called for in pre 2000 engines due to its narrow viscosity range, and the fact that it has flat tappets. More recently, with new roller cam followers/engine/ring designs, 5W-30 has been permitted. I don't know a thing about the CI-4 spec, but I do know that VII's when burned in a combustion chamber, leaves a lot of deposits behind. Some of these stay in the combustion chamber where they can accumulate and become known as carbon, some of them are forced down into the ring pack where they can stick rings. Further, I think that SUV oil/4X4 oil/High Mileage oil etc. is the biggest farce put on the consumers since Castrol started calling Group II oils synthetics. The reason I have chosen to use GC 0W-30 is because I learned on this board many months ago that this oil should not contain ANY VII's. Many other oils may meet the same requirement, including Amsoil, which is a fine product. The Northstar engine as well as several other GM engines are designed with a very agressive honing pattern on the cylinder walls. This is by design, and is intended to keep the rings well lubed, hence the long therotical engine life...the rings and cylinders will just not wear out. Now, start putting the wrong oil in that engine, or too much oil, etc. and strange things start to happen. The rings get stuck, oil consumption goes up, and a vicsious cycle begins. If you want to give advice on Toyota engines, be my guest, but when it comes to the Northstar you need to start checking some facts. There are many Northstars out there with more than 80,000 miles on them and many more with over 150,000 to 500,000 miles. Please don't let your personal biases in favor of imports influence the advice given on this board. I do not have anything personal to gain from any of this information and would just like to keep owners of Northstar engines on the right track with their maintenance and oil selection.