Being in the auto repair business I purchased a smoke machine for checking evap leaks years ago. It is a very handy tool for finding vacuum leaks and exhaust leaks also. I discovered a use that any engine builder might find very beneficial. As I was finishing up a repair on a customer's 390 ford engine, I decided to smoke test the crankcase. This would detect any potential external oil leaks and any internal coolant leaks. With the engine still on the stand fully assembled, I blocked off one valve cover and ingested smoke into the other. I was happy to find the engine was sealed up air tight. No smoke came out the coolant ports indicating the coolant passages did not have any major issues. Does this mean the engine will not leak? No......but it gives you a chance to catch any major leaks while it is still on the stand.