* Worn Piston Rings: Piston rings create a seal between the piston and the cylinder wall. Over time, these rings wear down, losing their ability to effectively seal the combustion chamber. This allows oil to seep past the rings and into the combustion chamber, where it's burned. This is a very common cause.
* Worn Valve Stem Seals: These seals prevent oil from leaking down the valve stems into the combustion chamber. As they age and harden, they lose their sealing ability, leading to oil consumption.
* Worn Cylinder Walls: Scratches and scoring on the cylinder walls, caused by years of friction, can allow oil to seep past the pistons.
* Breather System Issues: The positive crankcase ventilation (PCV) system is designed to vent gases from the crankcase. If this system is malfunctioning, it can allow excessive pressure to build up, forcing oil past seals and into the combustion chamber.
* Leaking Valve Guides: Similar to valve stem seals, worn valve guides can allow oil to seep past and into the combustion chamber.
* Improperly seated rings (during an engine rebuild): If a previous engine rebuild wasn't done properly, the piston rings might not be correctly seated, leading to oil burning.
The severity of oil burning depends on the extent of the wear. A small amount of oil consumption might be noticeable only as a need to top off the oil occasionally. Severe oil burning can lead to significant oil loss, blue smoke from the exhaust, and even engine damage.
