Confused over thermostat position in 5 cyl 4kq

[Leah Mueller]

I had my rad recored on my 86 4kq. The car began to overheat, so I replaced
thermostat, but it still overheats.  I let the car idle and when the fan
came on, I removed the expansion tank cap and the tank boiled over each
time the fan came on until the coolant was very low in the expansion tank.
It seems the new thermostat is sticking shut? I think I have put it in
wrong. It is a newer aftermarket style that fails in open position. I will
remove it today and check its operation in hot water. There is no
directional arrow on this one unlike the thermostat I removed. Should the
thermostat be parallel or perpendicular to the engine?

Thanks
David and Leah
86 4kq