Few drivers know that road tar can insulate metal and rubber surfaces. An oily film traps salt and grit from winter roads. This layer slows heat loss and can reduce cooling efficiency. It can also hide small leaks and harden rubber parts. Engine oil detergents do not fully remove this external layer. Use a cleaning liquid that is safe on paint, plastics, and hoses. For targeted removal of tar and grime, consider Tar remover and engine cleaner.