TSB - Coolant Loss M278 - M157 - M152 PDF

A service bulletin that addresses coolant loss issues in engines 152, 157, and 278. It outlines the complaint of engine coolant going low with no trace, identifying the cause as a coolant leak into the engine oil due to a defective molded seal between the timing case and the cylinder crankcase. The bulletin provides a remedy involving checks for external coolant leakage, inspecting spark plug holes for cracks, and checking for coolant in engine oil. It advises on pressure testing the coolant circuit and recommends seal replacement if issues persist.