Heater Plumbing....in-line valve

[cuda-cable]

In the process of putting my engine plumbing in and saw a couple cars this summer with a 'bypass valve of sorts?' in their heater hoses about mid way to firewall. I'd seen others with a 'shutoff valve' just in the one line feeding the heater core. 2 questions whats the advantage  and if so does any body have the part I.D.. for the bypass valve since it looks more of a factory correct thing to do.......also in a 340  what   temp of thermostat  should I  use.?........thx.......dk

[Chryco Psycho]

I believe the "bypass" valve was used on AC cars only

[gtx6970]

I believe the "bypass" valve was used on AC cars only

Correct, Water valve is the proper name, It's an AC car only thing.

[Chryco Psycho]

I use a 160 unless it runs above 160 all the time then I use a 180 * thermo