i have a 89 v6 merc 150 that runs hot. the alarm comes on but after turning the key off for a minute or less, alarm stays off starts up and runs. i have replaced thermostats twice, waterpump twice, poppet valve assy,temp sending unit. i installed a pressure gauge here is what it reads. 1500rpm 6psi ,2500rpm 10psi ,3500rpm 15 psi at 2500 10 psi temp gauges pins at 240 alarm starts screaming turn off motor wait 30-60 seconds start back up alarm off. as long as i drive 1700 rpm or less alarm stays off. sometimes i can wot 4-5000 rpm alarm never comes on.is there any way to pressure check coolant passages? i am wondering whether block or heads are cracked spark plugs show no sign of water lower unit oil stays water free.i have infa red gunned heads on lake and they are running hot.what should the water pressures be in gear under load? thank you for reading
