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 Suburban 2500 Intake Manifold Gaskets May Leak Coolant or Engine Oil
Chevrolet Suburban 2500 Problem
Engines Affected: 5.7L V8, 7.4L V8, Gasoline
Average Mileage: 98,989 mi (80,000 mi - 116,968 mi)
Visitor, 1998 Chevrolet Suburban 2500, 5.7L V8, 116,968 mi
Engine overheated due to loss of coolant x's. Shop replaced manifold gasket and oil switch, but DID NOT change oil. Oil changed at 117797. Engine failed (threw a rod)at 118870. Now I know why!
Visitor, 1999 Chevrolet Suburban 2500, 7.4L V8, 100,000 mi
at 75,000 miles the intake manifold gasket started to leek.
Visitor, 1999 Chevrolet Suburban 2500, 5.7L V8, 80,000 mi
had to have the gasket replaced they told me it was a common problem that happens on all 5.7's