Damage caused by overheating
Why the abrasions are visible all over the piston crown? What happens when the oil injector is bent or damaged and does not provide sufficient piston cooling from below? How does the abrasion on both sides of the piston occurs? Here you will find all the information you will need.
In the case of scuffing due to overheating, the oil film is broken. Initially, this causes semi-fluid friction and isolated seizures. The additional temperature rise at seizure sites eventually leads to complete lubrication loss of the piston. Abrasions become to appear as darkly stained and heavily scuffed spots. Depending on the cause of damage, scuffing caused by overheating occurs either at the piston skirt or the piston crown.
Abrasions caused by overheating that mainly occur on the piston crown
Description:
- Heavy scuffing, starting at the piston crown and running towards the edge of the crown.
- Abrasions all around the piston crown.
- The surface of the abrasions is darkly pigmented, scarred and partially scraped off.
- Abrasions on piston ring raceways, decreasing in the direction of the oil scraper ring.
Assessment
Due to the very high thermal load, the piston crown became so hot that the clearance was overcome and the oil film was destroyed. This caused a combination of scuffing around the piston crown circumference due to insufficient clearance and insufficient lubrication. The cause cannot be a general lack of piston play, because in that case the damage would start in the skirt area.
Possible causes:
- Prolonged high load during engine start-up phase.
- Overheating due to combustion interference.
- Malfunctions in the engine cooling system.
- Interference with oil supply (oil-cooled piston or piston with cooling channel).
- Deformed or faulty oil injectors, cooling the piston from below with insufficient oil.
- Incorrect sealing rings on the flanges of wet cylinder liners (see section “Cavitation of cylinder liners”).
Abrasions caused by overheating that mainly occur on the piston skirt area
Description:
- Abrasions visible on the skirt area.
- Surface of abrasions darkly stained, rough and heavily scuffed.
- Piston ring area slightly damaged or undamaged.
Assessment
As a result of severe engine overheating, there was a lack of cylinder face lubrication. This led to scuffing due to insufficient lubrication and severe scuffing of the piston skirt. The damage is concentrated in the piston rod area, there is often no damage in the piston crown area. Overload due to combustion interference can therefore be ruled out.
Possible causes:
- Engine overheating due to the following cooling system malfunctions: coolant shortage, dirt, defective water pump, defective thermostat, broken or slipping V-belt, insufficiently vented cooling system.
- For air-cooled engines: overheating caused by dirt deposits on the outside of the cylinders, broken cooling fins, interference or lack of cooling air ventilation.
