Q: Check engine on knocking engine milky cap but not in oil change loud knocking noise while driving and cold start up

Coolant leaks can be external or internal. If the coolant is leaking internally into the cylinders or crankcase, that will require a fairly significant repair. If the coolant is leaking externally, unless the leak is at the head gasket or the lower intake manifold, external leaks can be repaired readily. On the engine you have it was really common to have coolant leaks at the lower intake manifold, so common that the gasket there was completely designed and a different repair procedure was specified (higher torque on the manifold studs). To get the coolant leak diagnosed, please use YourMechanic’s coolant leak diagnostic service link. The knocking noise is obviously of concern. Unfortunately, typically, such noise is from worn bearings, connecting rods, and other major components. The noise might be accompanied by low oil pressure. My best advice is have the cooling leak diagnosed in case that is readily resolvable. The mechanic can evaluate the noise and if it is internal the engine will eventually have to be disassembled and rebuilt. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.