Royal Purple Duralec Ultra motor oil is specifically formulated to maximize performance and meet the demands of today's heavy-duty engines. Duralec Ultra is fortified with a high level of zinc/phosphorus anti-wear additive and Royal Purple's proprietary Synerlec additive technology. Synerlec creates a tenacious ionic bond with metal surfaces, providing protection upon startup and greatly increased film strength that helps eliminate metal-to-metal contact, even under severe conditions.