I have just swaped out my 1987's 350 for a 92 350. The engine runs great but it is not pumping coolant through the engine. Once I shut the engine off I can hear the coolant bubbling through the tubes and they get hot. I would think that the thermistat is working because it lets the coolant flow after the engine is off. Could it be that I have a big air bubble in the line and the water pump is not priming? This engine swap is my first time doing any kind of work on an engine, so I'm quiet new to all of this. I don't want to crack this block so any input would be great. Thanks guys.