First number in oil description like 5 in 5W-20 is viscosity when cold, so it only makes difference for the first few minutes before the engine warms out, otherwise at engine temperature 5W-20 and 0W-20 are pretty much the same. FYI 5W-20 was first used as factory oil in some 2001 year model Ford and Honda cars (Accord) so this type of oil is around for a while, even if TCH was the first Toyota car using it.