In one aspect, a method for detecting and diagnosing a coolant leak of an engine may include diagnosing a coolant leak of the engine based on a low frequency pressure response of a measured engine coolant pressure. In another aspect, an engine system (e.g., for a vehicle) includes an engine and a coolant system operatively connected to the engine. The coolant system includes a coolant reserve and a coolant pump between the engine and the coolant reserve. The engine system also includes a coolant pressure sensor to measure coolant pressure, and a controller configured to measure an engine coolant pressure and diagnose a coolant leak of the coolant system based on a low frequency pressure response of the measured engine coolant pressure.