& walai kum salam
thermostat helps engine to attain optimum engine operating temperature in less time, when T/S valve is removed it take LONGER and hurts engine performance. quietly mumble in front of him ... O gadhay kuch seekh lai
politely tell him to put back thermostat valve. by removing the upper hose pipe and losing less of coolant. once the valve is in system carefully add the coolant in radiator, read this to understand the cooling system of vehicle
once the valve in place you can see significant drop in needle position during driving conditions, and at this position in summers with aircon working. - keep check on coolant level in expansion tank ( reservoir bottle )