NEVER skip this step

Why do mechanics shave metal off of a car engine?! ⚙️🔧
When a car engine severely overheats, the massive heat causes the aluminum cylinder head to physically warp and bend! This breaks the tight seal between the engine block and the head gasket, causing oil and coolant to aggressively mix together.
To fix this, you can't just install a new gasket. The metal surface is no longer flat! Mechanics have to send the cylinder head to a machine shop where a massive fly cutter or milling machine is used to shave off a microscopic layer of the metal. This process, called "decking" or "resurfacing," removes all the high spots and old gasket material, leaving behind a perfectly flat, shiny surface. Without this step, the engine will instantly blow the new head gasket the second it starts!