Most cars use hydraulic valve lifters that rely on oil pressure to maintain a tight clearance between the camshaft and rocker arm. If the pressure isnt right, there is play between the lifters and the rest of the valvetrain, which causes a noticeable tap. Its possible that cold oil at startup may help pump up the lifters, but at normal temperatures the viscosity drops, and may be too thin to correctly work the lifters. As the oil breaks down after a few thousand miles it thickens, which eliminates the noise.
1 Heroin is a highly addictive and rapidly acting opiate (a drug that is derived from opium). 2  Specifically, heroin is produced from morphine, which is a principal component of opium. 3  Opium is a naturally occurring substance that is extracted from the seedpod of the opium poppy. (Generally, the purer the heroin the whiter the color, because variations in color result from the presence of impurities.) In the western United States, most of the heroin available is a solid substance that is black in color. 2  This type of heroin, known as black tar, may be sticky (like tar) or hard to the touch.
Heroin. Heroin is an illegal, highly addictive drug processed from morphine, a naturally occurring substance extracted from the seed pod of certain varieties of poppy plants.