35 Buick bypass thermostat

[Buick35]

I was wondering how the spring and valve inside the housing just above the water pump is what's called the bypass thermostat. It's below the thermostat that's at the bottom of the upper hose.Anyway, what's it's purpose and what would it do if it got stuck closed? Just wondering,Thanks.

[pont35cpe]

On both of my inline eight engines(`36&`41)I did away with the spring/valve, replaced with a 1" freeze plug pressed in the hole then drill a 1/4" hole in it.  This has been discussed here on the forum before..

[Buick35]

Thanks,I might do that.

[Brooklyn Beer]

And what is the purpose for doing that ?

 

[mfrank]

It's the thermostat bypass. When the thermostat is closed, the bypass opens and allows coolant to be pumped around the block, rather than through the radiator. Otherwise coolant flow would stagnate until enough heat reached the thermostat for it to open. The early Buick system is a milestone in thermostat design. I'm writing an E-book on thermostats, you can read about bypass designs here:

 

https://www.coolcatcorp.com/thermostats/Bypass%20Systems.html

 

 

[Brooklyn Beer]

Interesting and thank you!

[Ben Bruce aka First Born]

If I may.  The 1/4 inch hole is certainly not too big.   I know not when it started, but by 1950 there is a "bypass" from the bottom of the thermostat housing into the pump suction.  Always open. About thumb size. It WILL become plugged.  The rebuilder missed it. 

 

  Ben