2002 Chevrolet Express Van 5.7L Engine P0300 Misfire with Coolant Loss and Exhaust Steam
My 2002 Chevrolet Express Van (2500 model) with 39,000 miles is showing a recurring P0300 intermittent misfire code. Recently, I've noticed coolant loss and the vehicle runs roughly in the morning, often with visible steam coming from the exhaust. This strongly suggests that coolant is leaking into the combustion chamber or exhaust system. While head gasket failure is a common suspect, my van has never overheated—making this scenario less typical. Given the 5.7L V8 engine configuration, I'm wondering if an intake plenum or lower intake manifold gasket could be the root cause of both the misfire and coolant loss. The P0300 code may indicate a specific cylinder issue (such as cylinders 1, 2, 7, or 8), which might point to a leak in the intake system rather than a head gasket failure.
Lower intake gaskets are known to fail on this model. If the misfire is occurring specifically in cylinders 1, 2, or 7, 8, an intake manifold or lower intake gasket leak is a likely cause—especially given the presence of coolant loss and exhaust steam without engine overheating.