1980 L82/Overflow bottle/Overflowing

Original owner 1980 L82(47k mil). Last year replaced radiator,water pump, t-stat(160)and all overheating problems were fixed. Until today. After a short run about 30 miles highway, nothing heavy, temp. gauge normal, though i thought i detected the odor of antifreeze returned and parked it. Later in the day discovered the overflow bottle apparently overflowed after parking. Any thoughts on cause? TIA