No, look at Dr Haas charts (If that page has them, the old page did). Most all weight oils are within a small amount of viscosity of each other. Down in the low single digits. But at high temps, 300+, a VERY hot temp for any engine oil (but common on the racetrack), the difference is an issue. But at "low" temps like 250F (which would be pretty hot in a street car). the difference between a 0W20, 0W40, 10W60, isn't huge, but at low temps, 30F, 0F, etc, it is massive. Which is where the real issues lie. At that point you have a long time to get a 10W40 oil or 20W50 to the bearings compared to a 0W20. Its a flood of numbers Dr. Haas has in there to go over for the viscosity of each oil at what temp. But when you start comparing them at hot, xW20 vs xW30 vs xW40, etc, at hot temps they end up being a pretty small difference. But at some point, according to Dr. Haas, up the 300F+ range oil temp, it becomes an issue not having sufficient oil viscosity, and at 7500 rpm in a Ferrari with 300F+ oil temps, you NEED to maintain 75 psi oil pressure, add to that, a high G corner. You NEED it then. But when you drive that same Ferrari around town cruising the strip, 0W20 is the best choice in oil.

As long as the engine is mechanically sound, good oil pump, and not excessive bearing clearances, the engine, especially like our 1UZ/3UZ-FE engines, is going to love have 0W20 over 10W30, or even 5W30. Remember, 5W20 was a new oil, and may not have been oil in production yet. And not at all in the supply chain for Lexus, so they had to keep using what oil they had, 5W30, that was in the Lexus dealer supply chain.

I posted on Lextreme somewhere the 1UZ-FE engine rod and main bearing clearances compared to the 1UR-FSE (LS460 engine) and the 1UZ-FE was a fair bit tighter tolerances than the 1UR.

 

Thanks, I think I understand now.