SBC cooling question?
 

Have Dart Little M block (4.165"bore) , RHS pro elite 23* iron heads, ect... Running seapump, crossover with Hardin Marine Billet T-stat housing with no T-Stat (running reducer currently) with -12AN exits to exhaust with a 9/16" relief on top. Was looking to regulate the engine temps a little better. I am running a Hardin Oil T-Stat to remote oil filter and Cooler. Boat in South Carolina 90% fresh water. engine temps never really get above 114*. T-Stat for oil cooler is 190-200* and works very well. Was wondering if raising the engine temp to around 140* would help performance? Engine is basically brand new. Only put 16hrs on it this past summer since the build. Running 15w-40 oil based on clearances. Currently running the 3/4" reducer in the T-stat housing. Should i try a 140* with bypass and rely on the relief to cool the exhaust and relieve pressure off the seapump and everything in between?

If it was me, I'd run at 140-160.

Engine oil temp is mopre important than engine temp IMHO. That said, 120-140F is totally fine for coolant temps.

If you start playing with T-stats on crossover systems you'll really need to watch your water psi...can get out of control.

Most will use restrictors in place of tstat to get a little more water temp. Still be a good idea to see what your water psi is.

It's fairly cheap to put closed cooling on a SBC. Then you can run at a stable 170-180* San Juan Engineering has nice kits to do the job.

I am currently running a restrictor in the place of a tstat (the moroso 3/4"). it was the best one to regulate the water pressure. Was debating on trying a tstat with bypass holes but didn't know if the cross over (9/16" can tap to 3/4") would relieve enough pressure to justify even trying it? I know oil temp is good. No milky oil or condensation.

how would the fresh water cooling system work? I'm making 625hp. Also, given im running a remote oil cooler and filter head.

Put a circulating pump on the motor. Run antifreeze through the motor instead of raw water. A heat exchanger cools the antifreeze with raw water. All the high performance Mercury engines have closed cooling all the way up to 1350hp pump gas with closed cooling. It costs a little more up front but the motor will last a lot longer.

That's a bunch of stuff that hides your big power small block. You can still get your engine temps up by installing a thermostat.
Since the thermostat will restrict, you may need a dump valve before the engine which will keep your circulating water pressure down. They open at around 10 psi. I bet the original design will work fine unless you rev to big RPMs.

cpperformance.com shows the parts in their cooling stuff..

you will not gain anything from increasing the engine temp as long as oil temp is good, used to be the race car guys were saying made more HP warmer, everytime I put more heat in mine(alum heads) slowed down. Now they are using special coolers to get as cold as possible before a run..

huge possitives with closed cooling for marine apps. One alone is winterization, way much easier for closed cooled marine apps and the huge one is corrosion factors. Engines like constant temps, closed cooling offers and maintains better constant temps while running thry all RPM ranges for short a jist.

Side note........ still currently I have customers that have Volvo Penta 496's and Mercruiser 496's. Merc 496 all stock apps were closed cooled regardless from Merc, The Volvo/s came 2 ways non closed cooled in which mainly 85 % inland are and 15 % of Volvo 496's were closed cooled for the option to the buyer ( talking Inland boaters ).

Apples Apples same year models - almost same amount running times - side by side comparisons from lake waters and some brackish waters usage around the area - the closed cooled engines seem to have less problems and way less corrosion issues. . Another Side note.... seems that Merc 496's can have some water and or coolant leaks far more easier than either Volvo.