by Gary Proulx
Hemera Technologies / PhotoObjects.net / Getty Images
The piston rings fit into the horizontal grooves of the pistons. The rings expand against the cylinder wall and seal the combustion chamber. This ensures that the engine maintains a constant level of compression. Stuck piston rings are rare, but they do happen. There are two positions where the rings can get stuck. They can get stuck inside the piston grooves or stick to the cylinder wall.
If the rings are stuck against the cylinder wall, the crankshaft will not rotate. This condition usually occurs when an engine has been idle for a long time. The rings rust and stick to the cylinder wall. If an engine is seized, it is important to eliminate other causes, such as bad crankshaft bearings or broken valve train components, as these can also seize an engine. The typical solution to this condition is to pour penetrating oil into the cylinders. Over a period of days, the oil will generally release the stuck rings.
If the rings get stuck inside the ring grooves, they cannot seal the combustion chamber. A compression tester should be used to determine if each individual cylinder maintains compression equal to the others. The rings can get stuck in the ring grooves due to carbon build-up on the piston. They can also break off and remain in the ring grooves for many miles.
Gasoline in oil
A ring that is stuck in the ring groove allows unburned gases from the combustion process to enter the lower parts of the engine. This causes the engine oil to become saturated with these gases. If the engine oil smells like gasoline, it could indicate a stuck ring. Engines that are only used for short trips can also develop a gasoline smell in the oil. This is because the engine always runs at a low internal temperature and should not be confused with a stuck piston ring.
Higher crankcase pressure
The crankcase is vented to allow internal pressure to escape. This ventilation is managed by the PCV valve. When a stuck ring allows pressure to enter the crankcase, the PCV valve will overwhelm and internal pressure will build up. This causes oil to leak out of the PCV valve. Another indication of increased crankcase pressure is a dipstick continually being pushed up, away from the dipstick tube. In this case, the pressure has come out of the dipstick tube.