The intake manifold gasket may develop and external engine oil or coolant leak. In some cases, an internal coolant leak may occur causing coolant to mix with the engine oil. Running the engine with a coolant/oil mix may result in engine damage. Replacing the intake manifold gasket should correct this issue.Google+
Car Problem Reports
Chevrolet Express 3500 Intake Manifold Gaskets May Leak Coolant or Engine Oil
Chevrolet Express 3500 Problem
Engines Affected: 5.7L V8, 7.4L V8, Gasoline
Average Mileage: 89,750 mi (70,000 mi - 120,000 mi)
Visitor, 2000 Chevrolet Express 3500, 7.4L V8, 70,000 mi
twice now. first time payed for repair but the valley gasket slipped out at one corner and seems that the lower was over torqued... I am doing my self this time. I am not sure if I should use any "RTV" or sealant whatever...
Visitor, 1997 Chevrolet Express 3500, 5.7L V8, 120,000 mi
Leaking anti-freeze with smell, but no visible sign of leakage until gasket blew. Had to replace at 120,000 miles.
Visitor, 2002 Chevrolet Express 3500, 5.7L V8, 85,000 mi
smell engine coolant and notice its coming from intake manifold