I just finished upgrading the Cooling System on my 56. Nice new Water Pump, 5.5 Inch Water Pump Pulley, Aluminum Rad, 6 Blade Fan, Plug in the Bypass Hose, and a Genuine NOS Robert Shaw Thermostat. Everything works and no Leaks( hopefully) EXCEPT the Thermostat. Its like no Stat at all. Water is flowing into Rad as Engine warms up. It maxes out at about 120 Degrees.
This is the same thing I experienced a few Years ago with 2 Mr. Gasket Stats. Put a conventional 160 Degree Stat back in and everything is good. I did test it in Boiling Water and then in Cold to make sure it closed. Worked as it should. I have heard of these sticking closed but not open. Any Ideas? 

  

I did the same boiling water test on my Robert Shaw thermostat. Then I noticed my engine just wouldn't get past 140ish with a 180° thermostat. I took it apart to put in a 190° and discovered the t stat was broken and stuck in the open position.

Durham Missouri

The One I had trouble with previously I still have and retested it in Hot and cold Water. Still opens and closes as it should. This is the third Time I have tried using these type Stats and all  3 did the same thing? I am at a loss to understand why these type Stats don't work and conventional Stats work fine. And before someone asks-Yes it is in the correct way with point facing towards Radiator.

  

I just put the Conventional 160 Degree Stat back in and it works properly. I don't know how the Robert Shaw Stat is being bypassed and not working. I have ordered one of the Napa # 6 Stats and see how that works. 

  

Mark - Do you have these new t-stats drilled for the 3 bypass holes? I expect a fair amount of water to go through them when the engine is cold - when there is pressure on one side and no back pressure. It should be enough slow the warm-up process. If you've got the flow increased by the smaller pulley - and more air moving with the six blade fan - cooling equilibrium is going to be a bit different than before.

 
 Steve Metzger       Tucson, Arizona

I drilled it Steve. I tested it afterwards to make sure it opened and closed hot and Cold. There's hot water going into Rad within 2-3 Minutes as it warms up. Take it  for a drive which should bring it up to at least 160+. Nothing. It goes to about 120 and stays there. Never gets near 180. Same thing I experienced all 3 Times I have tried these. Even with the regular 160 Stat the cooling System is much better. Temperature is more level at about 160. Stop at a light and it doesn't change. Before the Temp would start to move up when stopped. On the right Track. Just wish the Stat would work properly. Even if there is a fair amount going through the drilled Holes it should still regulate minimum Temperature when driving and its not. Previously I tried these without the Holes. Same thing. Never warmed up to operating Temperature.

  

my 57 has temp gauge the left rear of the head and 1 at the intake at stat they are never the same. 1in the head measures the coolest part of the head 1 at stat measures the warmest part of both heads. my opinion you ar screwing up the whole cooling system. when you stop at a light if running a auto shift to neutral.you drop the load and torque cools down engine speeds up a bit. drilling the stat and restricting the bypass slows down the warm up.ys run the best at 180 at the stat nd as the stat opens slowley temp is controlled at ideal number. if you are in to summer or hot part of the land heating the whole system including the rad will not give you any reserve at stop lights or traffic. there ws a group who did a test on 57 bird and replaced all the shrouding and belting as was when new. had smaller pulley and 4bladed fan,un restricted bypass and had no issues. the better water pump for birds with the goofy spacers makes good sense. if you measure the temp rad at the top tank and the bottom withe a heat gun as long as there s 10 dgrs diference and huge at stat is under210 you are not over heating. if the top to bottom reading at rad has a greater difference the rad is restricted or pump is cavetting. 90% it will be rad issue. this is always a wild issue,especially with all we experts. WE THINK.good luck

r rigid?
Would you share with us what brands of water pump and aluminum radiator you used to get such good results?
Edit: and is the fan a flex or rigid? 

quote]Gene Purser (7/30/2017)

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I got the Rad off Ebay from Patriot Cooling. $225.00 Approx.  Made in Chine. Ships from California. Seems very well made. Fit perfect with no Modification. 3 Row thicker than Stock.  Has built in Transmission Cooler for Automatic. They seem to have One for most Applications.The Water Pump is a Cardone. I also added a 5.5 inch Diameter Water Pump Pulley and 6 Blade Fan Blade.

  

where did you get the Cardone water pump?