Radiator heat load of a Nissan V6 engine of 220 hp 2

Suggest you get a copy of the Standard Handbook of Engineering Calculations (Hicks, McGraw-Hill).
You will have to calculate the brake mean effective pressure and brake thermal efficiency (which you need the fuel higher heating value and engine specific fuel consumption). From the output energy (BHP) and efficiency you can get the input energy. The difference is what your cooling system has to reject (minus heat out the exhaust, direct radiation from the block and lube cooling). Exhaust heat from flow rate and temperature. The rest nil for conservative answer.
From the temperature difference of the coolant and lake water, the thermal conductivity of the stainless steel and flow rates (both coolant and lake) you can back out the surface area.
Running the coolant at a higher temperature will reduce the radiator size.
85 F Lake water? Are there hot springs nearby?

By mid August the shallow muck bottom warms the 24" to 30" depth at 4:00 PM to the point of being uncomfortable and checks out at 80F. Idling tied to the dock and neutral playing with it are a real danger.

You can probably get a lot of the thermodynamics answered on the thermodynamics forum. I found these sites which have some info:


About a third of the combustion energy goes into the cooling system and if your engine is a recent design you may get about 30% efficiency at best. If you assume you have to remove 250hp of heat you should be ok.

It's years since I worked on this but I found putting slight wiggles or kinks into the inside tubes improves efficiency (by agitating the flow a bit.) You can also tack a few mixing plates into the tube. Flow of the two fluids should be in opposite directions and it might be easier to double the cold water flow than double the surface area.

You can pick up brazed plate heat exchangers for very little at scrap yards and new they are not too expensive.

cheers, derek


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Even new brazed plate heat exchangers are not expensive, and the supplier will do the calculations for you.

Jeff

Thank you, OPENSOURCECAR. That is the information, (30 % ), I needed to supply to technical assist. Richard Petersen

If you are only idling or just motoring away, then the 85F lake temperature is very conservative. The engine is not putting out 220 HP. If you are relying completely on the boat moving to flow the water through the radiator, then you might have a problem no matter how large the radiator is. You might have to provide for a thermal siphon system or a small pump.

may have some useful tidbits

TTFN

It depends a lot on the design of the boat, and size and position of water pickup, but the type of boats I race typically run cooler the faster you go. These are about 18' long flat bottom or clinker design with typically SBC engines at 300 to 800 HP, no water pump, raw water cooling, typical ocean water temps, 1/2" dia water scoop, just behind the propeller, and in line with the prop wash.

Regards
pat pprimmer@acay.com.au
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If you're in North America, you might try calling the Calsonic office in Farmington Hills, Michigan. Calsonic produce the radiators for all Nissan products worldwide, and they have this information.
If you ask Marvin Beasley, he might even share it with you: tell him I sent you (grin).