where are you taking your water press readings from?
 

on the side of the block? intake?

I have closed cooling engines and I pickup the sea water pump pressure what at the inlet to the heat exchanger. Basically this is the first stop after the water leaves the pressure side of the pump. My oil coolers are on the suction side of the pump.

Side of the block, on one of the drains currently. In the past, I prefer to pull from the intake manifold, but on the current motor I had to go from the side of the block.

Is pulling it from the sea strainer too early or does it need to be after the pump?

LOL, you're not going to be reading any pressure on the suction side of a pump.

Mine are off the block and they have a tendency to clog up.

Thermostat housing. Had a plugged 1/8 in hole in the stock housing, why not use it.

Ken

ditto

In the intake or thermo housing. As mentioned, going in the drain hole in the block runs the risk of clogging up with sand/silt, etc.
Eddie

Some thermostat housings have extra NPT ports. That's what I used on my last motor.