The quick-connect fittings for the heater hoses tend to leak engine coolant. This problem commonly occurs because the metal housing has become brittle, which can break and cause leaks.Google+
Car Problem Reports
GMC Suburban 2500 Quick-Connect Fittings For Heater Hoses May Leak Engine Coolant
GMC Suburban 2500 Problem
Average Mileage: 96,000 mi (75,000 mi - 117,000 mi)
Visitor, 1997 GMC Suburban 2500, 117,000 mi
Coolant leaking from back of engine traced back to the quick connect fitting in left front top of intake manifold- I plan to replace the hose, or sealing ring if possible, since coolant is leaking from around the rubber ring at end of hose. I thought the leak was coming from a bad intake manifold gasket. What a money saving relief!
Visitor, 1999 GMC Suburban 2500, 75,000 mi
Caused heater hose nipple in front part of intake manifold to corrode and required replacement with new threads and larger pipe.