True. Your logic makes sense. I had a subaru oil pan apart before and the plug area is reinforced and built up to be flush with the end of the plug. I assume that this is the general case, since there seems to be like a dozen or so standard oil plug sizes that are used by most car/truck mfgs.

From Fumoto's FAQ:


Q. Does my Engine Oil Drain Valve protrude into the interior of the oil pan and prevent full drainage of my engine oil?

A. No. The threaded oil drain plug hole is always reinforced to accept the threaded bolt of the drain plug. In most cases, the Engine Oil Drain Valve will not extend past this threaded portion of the drain hole and will allow the oil to be properly drained. Your Engine Oil Drain Valve will let you drain your engine oil while it is hot without burning your hands and it is much more effective than trying to pump the oil out from above.

If assuming the above is correct, then the fact that the fumoto valves threaded section was the same size as the original plug, then there should be no drainage problem. But, next oil change I will measure to be sure <img src="/forums/images/graemlins/wink.gif" alt="" />.