HI-REV Engine Flush removes deposits, gums and varnish formed in the crankcase, cylinder walls, pistons and rings of an internal combustion engine. It cleans engines, flushes out contaminants and restores the engine operating efficiency. It also helps prevent new oil from being contaminated by removing the residue of previous dirty oil. Directionn Of Use : 1 Add ONE bottle Hi-Rev Engine Flush to old crankcase oil at safe level before changing to new oil. 2 Startup engine and run at idle for up to 10 minutes. 3 Stop engine and drain oil from crankcase. 4 Replace drain plug, fit new filter, add new oil.