The odd shaped port feeds hot coolant from the cylinder head to the primary thermostat (opens at 173 deg F) and heater. The round port next to the odd shape is where the secondary thermostat lives (opens at 203 deg F), also gets hot coolant from the head and provides additional coolant flow capacity through the primary stat and to the radiator.

 

Thanks. My 2017 Jeep Patriot has had a coolant failure. Running hot, heater blows very cold air (NE Ohio). Thermostat, water pump, or belt failure. Taking it in for service Tuesday.

 

If they replace the housing, ask them to replace the hoses too. My hoses were melted on. So I only replaced the housing seals including thermostat.

 

View attachment 101336
I didn't ask them to replace the hoses; hope I don't regret that. My Patriot is 8 years old but only has about 8,500 miles.....although the miles may not matter with aging hoses and other stuff, like tires.

If they replace the housing, ask them to replace the hoses too. My hoses were melted on. So I only replaced the housing seals including thermostat.

View attachment 101336
If they replace the housing, ask them to replace the hoses too. My hoses were melted on. So I only replaced the housing seals including thermostat.