Water pump back plate i.d.

[dmartin_egroup]

I have read the tech post about internal/external bypass differences and I am confused.  I have two 6 cyl flatheads, one is a 1949 Plymouth (by the serial prefix on engine)  The other is a 1945 Dodge WC pickup with its original engine (again, going by the serial prefix on engine).  I have two spare water pumps for these engines.  One spare pump is missing the flat metal plate that covers the back of the pump.  The other spare has the plate on it.  My question is in regard to a hole in this back plate, about 1/4 inch diameter, roughly centered on the area of the impeller.  Is this hole in the back plate part of a bypass system?  In the past, I have had the pumps off both of my vehicles but I don't recall seeing the 1/4 inch hole in either of those pumps.

 

Thanks for any help!

Dennis in West Tennessee

[JBNeal]

Water Pump Info

[dpollo]

That particular hole lines up with a larger round hole in the block and is intended only to allow air to escape.

Neither of the engines you mention require the pump with the internal bypass.  This is a hole of about 5/8 dismeter

near the top of the gasket surface which lines up with a hole in the block. This turns 90 degrees and goes up through the block to an extension on the cylinder head.  (1951 and up except Spitfire)

 

The bypass is a good feature but in practical terms, the cooling system works fine without it.