Hey Rick - thanks for the reply. The reason I was asking about a check valve is because I am considering installing an aircraft pre-oiler pump to flood the bearing surfaces with engine oil prior to cranking. I have sourced the pre-oiler pump and worked out how to suck engine oil from the oil pan, but am not sure about where to return the pressurized oil back into the engine. If I install the return line at the rear of the block above the factory oil filter, and if the engine oil pump does not have a check valve, the pre-oiler pump would probably be circulating engine oil from the oil pan in a loop back to the oil pan. The main purpose of the pre-oiler pump is to flood the bearing surfaces, but without an internal check valve I don't think it wll work. If in fact there is no internal check valve, and if there is no way to install one, I may need to run the return line to the front of the engine and connect at the turbo oil port. Or simply abandon the idea all together. That is the decision I have to make.