So I've got a modified 7.4. Around 600hp. Raw water cooling with a transom pickup and seastrainer. I've noticed when running hard my temp would fluctuate between 160-170, up to about 200 . Temp would Climb, thermostat opens, temp goes down then repeat. Probably every 10 Seconds. Im Thinking air lock? It just has a belt driven raw water pump, and a crossover kit with no circulation pump. Would an meziere electric circulating pump being fed by my raw water pump solve this problem? Is it common to just have the raw water pump and no circulation pump?

Put 2 or 3 of 3/16" holes in the thermostat and propagate a little bit of flow. That will level out your temp.

I had a 1/8" hole drilled in it but maybe I'll put a cpl more... is a raw water pump only , sufficiant for water flow?

Yes, plenty of people run with crossover set ups.
I think what you really need is water pressure gauge to troubleshoot what is going on.

I'm not sure if I might be wrong but everything I ever ran with a crossover didn't use any thermostat?

I tried that Smitty, but my blocks ran a little colder than even I liked. The holes essentially give flow at all times, but do restrict flow so I could build a little heat. The T-stat maintain consistency. Like Griff stated earlier I believe you need an H2O gauge to properly run a crossover. I conjunction with gauge you can restrict the bypass and control the pressure and flow in/through the engine.

I ran that exact setup and never saw what you are seeing, changing the pump not going to cure I do not think, those pumps move plenty, look for crap in p/s, oil coolers blocking flow, or maybe your transom pick up may be sucking air at times

Well, this is a brand new engine, the last one had some problems with water leaking into the engine thru a bad seal on the intake manifold and apparently also a casting flaw on my new brodix heads, so maybe the crankcase pressure into the cooling system had something to so with it? I'll run the same setup as before here on the new engine and see if it's the same . I'll make sure to put some more holes in the thermostat

i think you are building a lot of water pressure with the thermostat,a crossover is normally used without a t-stat on higher hp engines to help keep them cool.try removing the t-stat and see what happens.i agree that you need a water pressure gauge ,without it you are just guessing at it.

I would be fine running without a tstat. But I'm up here in Canada and the water stays pretty cool. I doubt id see any temp north of 130