STP Engine Stop Leak is formulated with a special agent to renew polymer seals and gaskets damaged by the heat of normal engine operation, which can otherwise result in oil leaks and expensive mechanical work. Engine Stop Leak for Petrol and Diesel Engines is compatible with regular and synthetic motor oils. Contains no solids to clog filters or inhibit flow. Will not harm oxygen sensors or catalytic converters. Helps stop minor oil leaks, and rejuvenates seals and gaskets. Over time, normal engine operation and heat can cause polymer oil seals and gaskets to shrink, dry-out and crack resulting in minor oil leaks. STP Engine Stop Leak is specially formulated to help stop minor oil leaks using a special agent to rejuvenate shrunken, dried-out polymeric seals and gaskets. It will also help to fortify oil with extra protection additives and a viscosity index improver.