cooling circuit

My 250 etec ho, after lending it out, is apparently overheating. Good stream at the indicator. Pump and impellor only have about 5 hours. On starting, temp on digital thermostat climbs to dangerous levels but alarm does not sound. If I go WOT for 15 seconds, when I power down to cruise it will...

I've read many post on this but technology is changing. So what is the newest and best sealant to use on all the cooling water connections? Thanks

H All I'm flushing the thin coolant hose on my DF115A that runs down from the top of the thermostat downwards. When I insert water at the top of the hose, I notice it comes out 1) from the water indicator tube ('telltale') on the oil pan, but 2) also from a small opening on the starboard side of...