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There are 2 seats in my LS1 thermostat. I know the seat near the return hose opens when the stat reaches it's set value. Can someone explain what the deeper seat is for or does? I am new to LS. I have installed a 6.0 in my 87 442. The stat is so far from the engine heat that it take a temp. over 220 to first open the stat then it runs between 185-180. Fan does it's job. FAST ez -ls is my controller. I have a 160 stat. I have not gotten the car out of garage yet. Still on jack stands. Thanks--Lee
when TS is closed, the BP opens easily to allow coolant from the block to go thru the pump;
when TS is open, the BP usually stays closed (i.e. is more difficult to open), this forces coolant from the block to go thru the radiator;
see attached coolant flow "schematic" I drew (I measured the spring rate and and surface area, from these I calculated the approximate BP opening pressures; and I traced the passages thru the pump, the circle and square represent the passages at the pump and block interface).
You should bleed out any air in the block (remove the hose from the steam-crossover tube connecting the heads, place a clear tube so you don't make a mess, watch the air passing out).
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LS1 thermostat ? 
