Like boats that were factory closed exchanger systems like the 496 and small blocks (if there were any) when you added a supercharger, or stroked it and added heads cam? Might just do closed system on my LS swap, and looking for some OEM exchangers that are up to the task because they are probably cheapest to get hands on since there was more volume of them made, or made be around used in good shape

See your having some issues getting answers (holiday season) to your questions (a few threads about the LS motors). If your in fresh water I would use open cooling and the crossover like mentioned in your other thread. There is an install guide which sort of list how to do it, look for the link.

If your in salt it would be best to close cool so long as the load on the motor is not to heavy. The weight of the boat, speed, amount of HP and other stuff. If you get into a heavy load then also will need a larger oil cooler and probably pan.

Brackish water mainly, but that crossover wouldnt work on my application. Has to have factory waterpump on it as the blower tensioner and idlers and everythign else are mounted to it
Already sourced out 2 qt filters to park alot of oil in the system. If I have to I could prob add another oil cooler into the loop later

Looking at this I cna roughly tell how long the exchanger is and find something similar in size or even larger. Thats what I was getting at if I can find a pair of OEM 496 exchanger cheap and adapt them to use and they can cool 650hp BBCs then they will likely be able to do the same in this app.

Hardin Marine - LS1, LS2, LS3 and LS6 Closed Cooling Kit - Copper / Brass
http://www.hardin-marine.com/instructions/625-4574.pdf

Not sure what the overflow fitting halfway up the tank would be for? Would need something with LS sized ports on engine loop preferably, seawater inlet likely 1.25" like that stuff is generally sized, and two 1" outlet ports to run to the exhaust for dumping the sea water. Wouldnt need to have that fitting in the tank necessarily for the cyl head purge hose, because we tap and run that back into the water pumps all the time with the cars with no problem

Oil cooler size depends on load. As an example, have a single 530 HP motor pushing a 11K boat. Had a 2x12 cooler installed and did not have a oil temp gauge installed. Working with a builder here, I installed a 2x18 (larger) cooler and gauge. First trip out my oil temp starts to climb above 260 degrees. This tells us that the original cooler was roasting the oil and the larger one installed would still over heat it. Have now installed a 2.75x18 cooler, dual AFR gauge and water pressure gauges. Hope to find out if we can finally after 3 years we might be able to keep the engine within proper limits.

If my boat was not so heavy, or I had 2 motors the oil temps would be less

The 496HO heat exchanger is the same size and capacity as used on the Mercury Racing 700SCI so it's adequate for your setup.

The heat exchanger is but the oil cooler cant be. The 496 oil cooler is tiny.


FWIW, you can buy a 4x16 or 4x18 in 10 seconds from Mr Cooler. Just calculate what you need, if its too big, you can put oil thermostats.

Well that makes me feel better, but it is a weird design the way it snaps into the manifold with the o ring seals (That are prone to leak) I was looking at this exchanger 4x21 same size but with built in expansion tank
91036A8 Mercruiser Heat Exchanger
Marine Parts Plus Accessories Serial Exhaust Cooling Systems And Extension Kits 898117 12493-75

I thought it was engine coolant in and out the 1.5 and 1.25 bottom outlets, and sea water pumped into the top corner 1.25 fitting and out of both 1" fitting in the expansion upper chamber to the manifolds and thru the exhaust overboard is how it was ran and that would be perfect, but after finding that last link Im not so sure????

KEM equipment in Tualitin OR does a nice LS heat exchanger setup they run on their LSA 555 hp and 605 HP setups with like 3 yr warranty so they don't have heating issues