I am adding these comments to the thread (which is now pretty old) due to the fact that we have learned more about these systems during the last few years and the following info could help someone troubleshoot their closed cooling system if it is overheating.
The CC closed cooling systems have been discussed in the past in a less than positive way (as you can see from some of the postings here), but CC spent a ton of money on their marine conversions, Hatteras obviously bought motors from CC, and I have to think any overheating issues were due to maintenance rather than poor engineering. Had their been a fatal flaw in the CC system it would sure appear that with all the expense they put into their engines, that they would and could have done something simple to tweak the system to make it work better.
CC seemed to over-engineer things. For instance, the whole notion of the THERMOCON DEVELO system is an engineered overkill by some standards, certainly Interceptor did not think a system like this was needed on their 427 motors, but I do not ever recall seeing an antifreeze based system on an Interceptor system either, just on Century inboards, and none of those use antifreeze and heat exchangers.
The sea water pump is pulling in 31 GPM at 4000 while the internal circulation pump is pumping 65 GPM internally. This internal circulation assures there are no hot spots inside the motors. The closed system brings in cool water, runs it through the oil and transmission fluid coolers first, and then into the heat exchanger and out the risers. In the event the motor needs any cooling it is up to the thermostat to tap into this cool water supply as needed, while still circulating internal water at 65 GPM at 4000. The system assumes the heat exchanger will always have enough cool water supply to feed the thermostat if it opens fully and needs more cold water. On a real hot day if the surface water is say, 75 or 80 degrees, then the heat exchanger can only provide water no cooler than 75 or 80 degrees, while if this same event happened in November the incoming water could be 40 degrees or maybe even cooler, so the thermostat really is the controlling factor. I will add that even the standard system is going to feel the effects of 75 or 80 degree surface temperature too.
When the system is wide open calling for cool water, if the sea water pump is not pumping the prescribed volume of water flow, if there is an air leak in the sea water intake water line that reduces flow, if the heat exchanger happens to be clogged with debris that compromises the water-to-water heat exchange, if the t-stats are wrong temperature range or perhaps stuck, if the Pressure Regulator Valves are not functioning as they should and perhaps are stuck in the closed position thus restricting flow, if the radiator cap is not pressurizing the system properly, then any of these items or a combination of one or more can contribute to overheating in the Chris Craft engineered closed cooling systems.
On the closed cooling system, the Pressure Regulator Valves will open at 2-psi and continue to open as pressure builds, enabling the full 31 GPM to be run out the tailpipes. There should be some math that can evaluate the ability of basically seven 5-gal containers of water flowing through a motor in the course of 60-seconds to handle a certain amount of BTU's, using originating water temperature as a variable and the ability to exchange heat via copper coils as a constant. On my 427 Lancer project motor I removed the internal circulation pump alltogether, because I am relying on just the 31 GPM to pull out the heat: even at that there is a concern that the motor will run too cool.
On the closed systems at all times there is an outlet at each PRV allowing full time water in limited quantities to be flowing out the tailpipes for obvious reasons, to avoid having the system overheat and burn the rubber exhaust hoses. In addition to this full time flow, when the system feels 2-pounds of pressure then the PRV opens up and allows full flow out to the risers also allowing full capacity heat exchange.
Some people have removed the PRV from the closed cooling system with the thought that this will allow more flow through the heat exchanger. We have speculated why the PRV exists on the close cooling motor in the first place, but since then I have learned a lot more about the systems and those PRV must be there to force water through the heat exchanger in a predetermined manner to avoid air pockets (that's my guess anyway). On the Standard System they have a more understandable use, but I would not be too quick to toss my PRV on the closed systems. On the closed system the PRV is operated frequently so it is well exercised on these motors. In the event one clogs up however and will not open fully, then it absolutely could cause overheating due to restricted flow.
I suspect radiator caps may have been overlooked by some owners. In addition, there is a water wetter ingredient that can be used along with antifreeze mix that is reported to help in some motors, do not know about the CC marine systems. We always look at the heat exchanger as the culprit for overheating, but as I noted above, there can be many parts of any closed cooling system that must be working properly for the overall system to work.
I have commented on the water stains I have seen on some of the closed systems, and I equate this to overheating and a boil-over, but it could be a simple matter of overfilling the system too full and when the water got warm it expanded and guess what happens then.....it comes out the cap or somewhere else onec pressure builds.
That's about all I know about the marine closed cooling system. I can't help but think that CC engineered this system to work better than some people have reported. After all, some people don't change oil regularly.
Anyone able to add to this thread please do so, there are lots of these systems out there in service today, and any tips we can add to this thread are subject to potentially helping someone some day.