I just installed a new exhaust manifold on my OMC inline4 Ford and it was smoking pretty bad and it got really hot? I installed a used manifold because they don't make them new anymore. It came put together riser/exhaust manifold and I had noticed there was something jingiling around in it. I figured it was just something from the packing or some minor rust that would flush out when started while water and exhaust ran through it. Not sure why it was heating up so bad and smoking I did just install a new water impeller in the lower unit?? Any sugestions??