I have a stock 525sc . only thing that has been changed is it is setup with a crossover now in the front. The boat also has a through hull pickup to a sea strainer. When idling on the hose or in the lake the boat runs 180* and if I try to cruise at 2800rpm or greater it will rise to 210 . the boat has no thermostat. I pulled the impeller today and it is complete no missing fins and only small wear on the housing. Also back flushed through the oil cooler and got no debris. Any ideas why the boat is running this hot when it should be at 150ish

Dumb question, but do you have good water flow from the exhaust, and is the sea pump plumbed properly, meaning the LH out on back of sea pump is going to the crossover?

Yes plenty of water flowing out of the exhaust it seems to me and yes looking at the back of the pump. The hose tightest to the block go to the oil cooler

On the back of the pump it should be labled "LH OUT" or "RH OUT". the hose feeding the engine should be hooked to "LH OUT".

Since you probably removed the stock water temp sending unit, make sure the sending unit (if original) is grounded properly. If sending unit was replaced, make sure its the proper sender for the brand gauge. A bad ground/incorrect sender can give high readings. I had this problem a few years ago. Would show 150ish at idle, and creep towards 200 on plane. No thermostats in mine with crossover. Found a bad ground behind dash, fixed that, gauges stay cold now.