1991 mustang gt. Was running 1-2 notches below red line on temperature.. which is still high.. flushed radiator now runs way above red line.and stays there. But when I start it when car is cold shows it at normal temp. And rises fast. But when use infared on water pump and neck shows 160-170-180.. am I checking the right area with infared? Could it be my thermostat? Or my coolant sensor? No water in oil..No coolant is spilling out of radiator ..