rislone zddp additive is an additive used to raise the zinc/phosophorous (Zinc dithiophosphate) levels in motor oils for older engines that require higher levels of this additive. It's also a good addition to oil when breaking in a rebuilt engine. The high Zinc levels act as a sacrificial barrier between the new metal parts during break in. However, too much zinc is bad as it will bond to the elements in catalytic converters and clog them up. The correct level of zinc/phosophorous is 1,400-1,500 ppm. Rislone has two products available for this purpose: the old but now discontinued quart bottle (part number 4401) and the newer triple concentrated formula that goes into a 1 qt jug (part/product number 4405).

This performance "booster" is intended to be added to petroleum based motor oils of any type. It is formulated to provide the metal protection modern conventional motor oils lack to keep flat tappet camshafts and lifters working properly in older cars, trucks, hot rods, daily drivers and racing applications. It contains high levels of Zinc and Phosphorous EP (extreme pressure) additives along with mixed esters to help better lubricate internal engine components such as pistons, flat tappet camshafts, lifters, pushrod tips and the rest of the valve train. It also stabilizes the motor oil to insure against viscosity and thermal breakdown reducing friction at start up and eliminating dry starts. It also helps to prevent the formation of sludge and sludge deposits.