Help please, where I can install water presser gauge? On the block or on the intake manifold?

either side of the block or the t stat housing.

What motor/year?

In the block drain plug hole or in the intake manifold. The ones in the block drain tend to clog easily if you run in any shallow water.

At the present it is set on the thermostat housing. I have 15 PSI pressure on the gauge. I would like to know what is the safest pressure to have on the block or intake manifold cos i am experience a problem at 4000RPM the inlet hose on the fresh water pump is blowing. temperature with thermostat housing is always to normal.

25psi is about the max you want. You shouldn't being blowing hoses even with 40 psi though.

when i put on the thermostad i find a blow hose always the same one. from the pump to the oil cooler.

Have you back flushed it to look for impellor parts clogging it?

High pressure before cooler and lower pressure after the cooler.

I agree, check for an obstruction in the oil cooler. Water should flow through it almost as fast as a straight hose.

i checked all the hoses and the cooler, ok and clear.

is this a new problem ? if so what did you last change also I run W.P. gauges at my helm also run pressure relief valves and dumps off the side