160 degree thermostat doesn’t work

I have 6BTAs that ran 195-200 degrees. They were always within a few degrees of each other. Higher when FL water temps are elevated in the summer. For safety, I replaced my 180 degree stats with SMX 160 degree stats. Now one engine runs cold @ 140-150 and other hot @ 195-200. Impellers are new. Fuel coolers clean.  After coolers and trans oil coolers spotless. Just did heat X maintenance on engine running hot. Replaced antifreeze. Did exact same service to each engine. <br />Does not make sense. Laser pyro gun shows one engine runs hotter than the other. Temps same/close coming out of after and trans coolers. Exhaust water temps are similiar. In between way off.<br />I did not drop thermostats in hot water to check opening before install. Are there any reports of BAD thermos shipped?