Yes, a loose coolant cap can absolutely cause an engine to overheat. The coolant cap serves a crucial function: maintaining proper pressure within the cooling system. When the engine heats up, the coolant expands. A properly sealed cap prevents this pressure from escaping, allowing the coolant to remain at a higher temperature and transfer heat more efficiently.
A loose cap allows pressure to bleed off prematurely. This lowers the coolant's boiling point, causing it to boil and potentially overheat much sooner than it otherwise would. The loss of pressure also reduces the cooling system's effectiveness, contributing to overheating.
