I don't know about a 25, but I have a 1975 Evinrude 9.9 that did not have one. You could only tell if it was pumping by looking at the exhaust port after the thermostat opened to see if it was spitting water. If it was not pumping you would have burned the impeller up by the time the thermostat opened. I did not like that so I made my own. I drilled a hole in the water jacket and tapped it with a small pipe tap. I then installed a line from it to one on the drain holes on the bottom of the motor cover to where I could see it peeing when I started it. It makes me feel better looking back and seeing water coming out of the "pee hole".
