2005 yamaha 150 low water pump pressure

I have a 2005 yamaha four stroke that has low water pressure. I have replaced the impeller and housing with no change. has anyone else had this problem?

[boats.net]

Is it overheating? What is the water pressure reading on gauge at wide open throttle?

You may need to clean out your poppit valve (pressure relief)

Is it overheating? What is the water pressure reading on gauge at wide open throttle?

I don't have any water pressure gauge on the boat. Yes it has overheated a few times.I also don't have a temp gauge just a buzzer. Thanks for your help

You may need to clean out your poppit valve (pressure relief)

What does it look like and where is it located?

[boats.net]

Number 6 in this diagram is the pressure control valve and number 18 is the thermostat. Yamaha Outboard Parts 2005 F150TLRD CYLINDER CRANKCASE 2 Diagram