The Owner's Manual recommended oil viscosity for 2JZ-GTE is 10w-30, but my Supra is far from stock. After hard driving, i checked the oil viscosity and it looked like water. I am afraid 10w-30 might not have enough viscosity.
eh, might be getting hot, do you have a aftermarket oil cooler? that might help that, if you still think its too thin try working your way down, maybe a 10-40 next time, 20-50 is thick as hell and i use to to slow some oil leaks more than anything. sorry i dont have access to anything that can help ya might want to try the mk4 section
p.s. 10-30 is usually a "all temp" kinda oil, usually if you check they have different options for diff temps, as they usually have a few that overlap