Why a door closer leaks oil

Why it cannot be repaired

The body holds oil under pressure behind a piston. Closing speed is controlled by how much of that oil is allowed past small valves. There is no filler port, and the seals are not a serviceable part. Once oil escapes, the damping goes with it: the door starts closing faster than it should, and eventually the spring slams it.

The commonest cause is an adjustment mistake

The speed valves do set the closing speed — that is what they are for. What they cannot do is make an undersized closer behave like a larger one. Half a turn is one increment, and the limit is physical: turn the adjusting screw out far enough that it passes the port it meters, and oil escapes past it. If half a turn in each direction has not given you the speed you want, the closer is the wrong size for the door, and winding the screw further is how a sizing problem becomes a leak.

Other things that end a closer

• Being used as a door stop. Forcing a door past its designed opening angle loads the arm and the body in a direction neither is built for.
• Impact: a door blown open by wind onto a wall, repeatedly.

If a closer leaked within its warranty period and was not forced, over-opened or backed out past its valve seats, tell us the model and what the door is. That is a conversation worth having rather than a part worth replacing quietly.