Ever since i bought my boat the temperature is always up and down at cruising speed (150 to 175 to 150 to 175). This year i installed a preesure gauge and the pressure reads 15psi at 175deg and 24psi at 150. Any ideas?

I noticed this with a crossover setup. The temp and pressure gage look like windshield wipers. When the temp goes up the T-stat will open and block pressure then will drop. Then the t-stat would close and block pressure goes up. I solved it by drilling larger holes in the t-stat to help it stabilize and adjusted my dump valve. Start with several small holes in t-stat or replace it with a new one. Stock setup?

The motor is a 00 502 mpi .