When it comes to replacing your old manifold with the new & best intake manifold for the chevy 350 engine, there are various symptoms that you can check out. One of the most common symptoms is the degraded engine performance that makes the air leak out. You will also see white smoke coming out of the exhaust system, leakage in the coolant, and reaching the oil pan. Furthermore, the coolant leakage leads to engine overheating. Thus, you can analyze whether your engine needs a manifold change with these daily signs.