What are people using for closed cooling on ther ls engines? Hardin Marine makes a system but is there any other players in the game yet

about min of 6 other players at least. And IMO R&D is top notch and high end plus they can manu for custom applications, any size and different shapes.

Look at what Volvo Penta has as well. They have done a lot of testing with the LS set up and cooling. They also like to use plate coolers as well on their LS apps for some other info.

You get a heat exchanger from Mr Cool and fab up yourself using stock water pump, or the make adapter plates to use a BB chevy pump on a LS using one in a LSX mustang race car now, either way would not be that hard