Excessive pressure in a car's cooling system can lead to engine damage and system failure. Below are the common causes explained in points:

1. Faulty Radiator Cap
The radiator cap maintains the system's pressure. A defective or incorrect cap may fail to release excess pressure, causing it to build up.

2. Overheating Engine
High engine temperatures cause coolant to expand and generate excess pressure. Overheating could result from a failing thermostat, insufficient coolant, or a malfunctioning water pump.

3. Blocked or Clogged Passages
Clogged radiator or coolant passages prevent proper flow, leading to localized overheating and increased pressure within the system.

4. Blown Head Gasket
A blown head gasket can allow combustion gases to enter the cooling system, significantly increasing pressure and introducing air bubbles into the coolant.

5. Thermostat Malfunction
A stuck-closed thermostat restricts the engine's and radiator's coolant flow, causing overheating and pressure buildup.

6. Cooling Fan Issues
Non-functioning or inefficient cooling fans fail to dissipate heat from the radiator, leading to higher coolant temperatures and pressure.

7. Excessive Coolant Volume
Overfilling the system leaves no space for thermal expansion, leading to pressure spikes as the coolant heats up.

8. Cracked Cylinder Head or Block
Cracks in the engine block or cylinder head can introduce combustion gases into the cooling system, increasing pressure.

9. Air Trapped in the System
Air pockets from improper bleeding after a coolant change can expand when heated, creating pressure surges.

10. Use of Incorrect Coolant
Using the wrong type or mixture of coolant can cause overheating and chemical reactions, leading to pressure anomalies.

11. Damaged or Restricted Hoses
Collapsed or restricted hoses obstruct coolant flow, causing localized pressure increases in the system.

12. Water Pump Failure
A failing or underperforming water pump cannot effectively circulate coolant, leading to uneven heat distribution and pressure buildup.

13. Radiator Issues
Corroded or damaged radiators reduce heat dissipation, disrupt coolant flow, contributing to excessive pressure.

Preventive Measures:
Regularly inspect and replace worn-out components like the radiator cap, hoses, and thermostat.
Use the correct coolant type and maintain the recommended levels.
Ensure the cooling system is appropriately bled to eliminate trapped air.
Conduct timely maintenance checks to avoid overheating and related issues.