Engine internals

Piston cooling jet

Sprays oil under the piston crown to carry heat away.

Drag to turn it Open in the 3D lab
Where it sits

In the crankcase, aimed up at the underside of each piston.

How it works

A calibrated nozzle, often with a pressure valve, opens at a set oil pressure and directs a jet at the crown.

Think of it as

A shower that cools a hot plate from below.

Symptoms when it fails

A blocked or misaligned jet can let a piston overheat; symptoms usually appear only as engine damage.

Lifespan

Usually condition-based rather than a routine replacement. Lubrication, overheating and the exact engine affect wear.

Repair cost

Internal-engine work is usually labor-intensive. Diagnosis and the engine code determine the repair scope.

The BMW angle

Turbocharged BMW engines such as the B58 rely on piston cooling because boost raises crown temperature.

Used in

BMW petrol and diesel engines; petrol-only systems are identified individually.

Sources
Same system

Engine internals

Engine blockHolds the cylinders and supports the engine’s rotating parts.Cylinder headCloses the cylinders and carries the valves that control breathing.Cylinder-head gasketSeals combustion pressure, oil and coolant between the block and head.PistonReceives combustion force and moves up and down inside a cylinder.Piston ringsSeal combustion gas and control the oil film on cylinder walls.Connecting rodTransfers piston force to the crankshaft.CrankshaftTurns the pistons’ back-and-forth motion into rotation.Crankshaft main bearingSupports the crankshaft on a controlled film of oil.