700 sci - over heat at high rpm only
 

Engine will run at under 3500 rpm all day no issues , within 2 minutes of the rpm being raised water temp rises and the alarm starts ..

. I stop put engine in neutral and raise the rpm to 1000 and temp will drop to normal and the alarm will silence , I only raise the rpm to increase water pressure a little and stop that screaming alarm sooner . water pressure runs around 20 psi at 2000 rpm and climbs with rpm ...

Sea strainers are clean .

Sea pump had new impeller last summer ..

I'm stumped ...anyone got any ideas , suggestions ?

Stuck partially open thermostat ?

I would guess it's the impeller. I change mine every spring and every 30 hrs during the summer.

Heat exchanger clean? Also impeller and housing r & r, they are not expensive to change more than once a year.

Blockage in the exhaust? That'd show high pressure regardless of flow.

+1 on changing the impeller. Should be done at least once per season at minimum.

Are you overheating to the point of bluing the headers at all? If so, you will want to pressure check them at the end of the season or now with compressed air.. overheating those headers contributes to their failure..

do you have a water pressure gauge ? if not do that now and see what pressure...that will tell you which side of the cooling the issue is..also assuming the smartcraft is going off...make sure the sensor is not bad, try swapping them to make sure you are not chasing a non cooling issue...Rob

many times the cooler is embedded with crap in the tiny little holes . can clean them . as stated also check your heat exchanger.

Did it ever smoke an impeller? If so, were all of the pieces found? They can make there way into the coolers and heat exchanger and really plug them up. I would install a new impeller and housing (if needed) and start removing water hoses and back flushing them. You can remove the end caps of the oil cooler and check it for obstructions.
Eddie

I had the same issue happening to one of my customers boats, it ended up being a blown head gasket. 700 SCI in a 36 MTI.