It depends on the additive. Most detergents, dispersants, FM's, rust preventatives, anti-corrosives and antifoaming agents work mostly at all temps.
Pour point depressants work at the lower end of the scale while Viscosity Index Improvers (VII's) work at the higher temps.
Anti-wear agents and anti-oxidants work at the higher temps and at higher loads.
So temp is just but one item in the equation, you also have to throw in load (and RPM) as another variable at which additives start to work.
[ November 20, 2002, 08:07 PM: Message edited by: MolaKule ]