I'm using GC in my Northstar right now. It seems fine, and certainly doesn't need to be "thickened" up. It's a little early to tell much about usage, I think it's been in less than 1000 miles. I have only added about 1 or 2 oz. of oil to it, just because I am watching it very closely. Gas milage seems to be down just slightly, probably due to the 12.1 cst weight. The engine runs very well with it, VERY smooth and very quiet.
JohnBrowning, I usually agree with your posts in general, but I'm going to have to disagree on this one. The Northstar is a fantastic engine. It delivers over 1 HP per cu. in. and meets all pollution regs, is consumatetly driveable, and gets 27+ MPG in the process. The engine is designed to go 300,000 miles if taken care of properly. And as usual, this last one is the rub.
This engine is designed at the upper limits of conventional technology. The top ring of the piston is about 1/16" from the combustion chamber and gets really hot. It is one of the reasons "SL" oil was designed. The SL's have fewer VII to stick that top ring. Most of the problems with oil consumption in a Northstar are due to 2 things, not driving the engine HARD enough, and keeping the oil level at the "FULL" mark when cold. This engine, which holds over 7.5 quarts of oil, should only have the oil level checked when it is hot. To fill the crankcase to FULL with the engine cold starts a viscious circle of events that eventually cause the (low tension) rings to stick. Yes, some of the flushes mentioned here may help temporarily, but if the owners don't break some old habits, oil consumption will return. When I bought my used '99 it was using about 1 quart/1000 mi. I have since been able to get that down to about a quart/6000 miles....without the use of additives or flushes. If you guys really want to know about Northstars, just say the word. This post is too long already.