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
GMC Yukon Denali Intake Manifold Gaskets May Leak Coolant or Engine Oil
GMC Yukon Denali Problem
Engine Affected: Gasoline
Visitor, 2000 GMC Yukon Denali, 170,000 mi
Denali started overheating and was losing antifreeze. Diagnosed and fixed by local mechanic but replacing "defective" intake manifold gaskets.