so the problem is the boat will have 20lbs of pressure for the first 1/2 mile the boat is on plane , then the pressure drops slowly from 20 to 0 lbs in then next 600ft . then the temp goes from 140 to 195 and sounds the alarm ,after you go back to idle the temp will slowly go back to 140


we have no leaks
replaced the impeller
cleaned the strainer
replaced the thermostat
checked the block water pump
checked the oil cooler for blockage
checked the impeller housing for cracks
no water in oil
no visable hose kinks or blisters



the sea pump is moving water because the water is swirling in the strainer and spitting out the exhaust

IDEAS ?

Check for belt slippige so
Something could've getting warmed up and seizing or. Belt heats up loosens up enough to start slipping. Especially a v belt setup , check width on v belt if equipped ?

Do you have a fresh water flush system? If so, does it have a ball valve or check-ball in that system at all? There could be debris impeding flow at that valve if so; as I have seen that happen on more than a few boats.

Did you replace impeller and housing at the same time or just impeller? Replacing in a pair yields much better results, use Merc brand also.

I had the same issue.

After chasing my tail for hours, a friend looked at the housing.

Changed it and this were right again.

Ken

serpentine belt , will check

thanks for the idea

no check valve in mine .

thanks for idea

used merc brand impeller , will replace housing . just surprised because it does have pressure then looses it

I will replace the housing this week

Replaced the housing and another new impeller . Changed another thermostat , changed the inlet hose to the sea strainer and sea pump . Changed seals in the impeller shaft also . Tightness checked on the belt also