US1 Fountain

You are misinformed. That is not enough pressure to give a complete fill, possibly allowing for air pockets in the heads, and possibly a higher false temp reading because the sender may be registering a steam pocket, not water temp.
Stock HP500's will have around 15-20 at WOT. Since you stated new circulating pump and t-stat, that eliminates a crossover setup which will give low pressure.

Something is blocked/not right. Double check the inlet supply hose from the transom to the sea water pump for blockage or a kink. That hose HAS to be hardwall. You can't squeeze it by hand. Also remove the hose on the outlet side from the seawater pump, then remove the hose end right before going into the t-stat housing and back flush that line making sure no broken impellor parts come out a tthe seawater hose end.
You did install the hoses on the right ports when you replaced the impellor? That will give the symptons you are seeing too. If all checks ok, check the flow from the drive pickup to the seawater pump.

Good Luck

FOUNTAINFAMILY

Thanks for the info. I will look into the hose routing and see if there is any blockage anywhere. t we will be on the lake this weekend on sunday.

tnothin

Hey Fam. Dont you live at Disco. Bay, so what lake are you goin to. I want a ride on your boat Ha Ha but seriousley lets meet up sometime. My name is Chad call me if you want man
916-837-1379 we'll have a cocktail.

FOUNTAINFAMILY

We are headin up to Berryesa on Sunday. We have a 4 year old and it will be her first trip out. We live in Green Valley.