engine temp low after overheat and new head gasket

several years back i snapped a belt while driving and my truck overheated, had the head gasket replaced along w thermostat after that my temps maxed out at 185 on a 100+ degree day but usually was around 176 on a regular day. fast forward it slightly overheated on me again after one of my belts snapped and i thought the headgasket was fine so i drove it as is for about a year and a half. well the headgasket finally gave in and it started getting coolant in the cylinders. i had the gasket replaced and thermostat as well and now my normal driving temp is around 172. i have seen it drop as far as 168 degrees. what could be causing this? should i be concerned? i used part #90916-03120 for the thermostat which i believe is the 180 degree one. also the only code i have is p0401 which i have yet to figure a solution for. not sure if it has anything to do with the low temperatures.. thank you

 

Thermostat stuck open? I know it's new but that doesn't mean it was good. Does it take longer to warm up that usual?

I gotta say it. You know it's cheaper to change the belts before they break right?

 

Start simple, there may be an air pocket preventing the sensor from reading correctly.

Check the level and burp the system by squeezing the top rad hose.

 

had the thermostat tested and it functioned fine, also this is the second thermostat ive put in what are the chances both have been faulty? also yeah i know the second time the belt snapped cause my harmonic balancer was acting up. i have since fixed the balancer.