Need help with thermostat installation

[grubby65]

I have a 1937 DeSoto with a 1951 S-15 motor.  The previous owner kind of put it together with a mosh-mash of parts.  I was going to replace the thermostat so I purchased one for a 1951 DeSoto.  When I pulled the old thermostat out there was a piece of hose about 1/2” long on top of the thermostat, about twice as long as the rubber seal which came with the new thermostat.  The part # on the thermostat housing is 640726.  My guess it is for the 1937.  Any thoughts would be appreciated, I’m assuming I need to get a thermostat for a 37 or the housing for a 51

[dpollo]

the 37 has an external bypass hose, one inch in diameter, which connects to a fitting on top of the water pump. The thermostat housing also aligns the top hose with the radiator.   51 and newer engines (except some "Spitfires)  have an internal bypass making additional plumbing unnecessary.

 

[Andydodge]

Whilst these 2 pics are not the best they do show the Internal By Pass thermostat setup that my Plymouth had.......you can see that there is no other connection of any sort apart from the large upper radiator hose that is attached to the thermostat housing bolted to the cylinder head...the "by pass' setup was done via an "internal" cast hole in the engine block connecting to a similar hole in the back of the water pump.....on an external setup the connection or hose is as dpollo explains.............as your car sounds like it has the external setup then thats what I'd reattach.......a pic would help confirm tho'.............andyd 

[Sniper]

It needs to be mentioned that you can run an external bypass on an internal bypass engine.  But not the other way around.  The block and head determine the feasibility of running an internal bypass because that's where the plumbing is.  So if you have an older engine without the internal bypass passageways in the both the block and head and you do not run the external bypass setup you will have no bypass at all. 

[dpollo]

in practical terms, you can live without the bypass .  the heater circuit, if open, will allow circulation.

[Sniper]

Some of us live in the desert and the heater being open is a bad thing most of the year.

[dpollo]

It is possible to bypass the heater core altogether, but it will remove heat from the engine if needed.