Closed Cooling System

Just bought a boat with a closed cooling system and I have never seen one in person. Tried looking for some info on them but not cooming up with much. I imagine water comes in the boat and there is a heat transfer coil or tubing that cools the coolant. Is this right? Is there only one impellar, how does the coolant stay cool, and is there anything you do to winterize other than channge oil and treat gas?

The close circuit will be for the engine, and posibly the manifolds, but that type of setup is uncommon. The raw water will come in and be pumped by the external water pump (rubber impeller) through a heat exchanger, and into the manifolds, then through the risers and out the exhaust. The closed circuit on the engine works just like a car, with a regular water pump (circulating pump) on the engine, keeping hot coolant flowing through the engine and heat exchanger. In the closed circuit you should have a water/antifreeze mix just like in a car. This side of the system requires no winterization as it cannot freeze so long as you have an appropriate mix of antifreeze/water.

Thanks, that clears some things up. So there is just one rubber impeller for the raw water and the other is a water pump with no rubber impeller just the metal one. Is there anything special I need to check on the closed cooling system or when it has enough fluid it should be good to go.

Nothing special about it. Just change out the water/antifreeze mix every few years like you would on your car, check the fluid periodically to be sure you don't have a leak. This should be running regular green antifreeze like a car, not RV or any special antifreeze. Winterize the raw water side of the system the same way you would a completely raw water cooled system.. Drain anything that holds water (manifolds, heat exchanger, raw water pump, any low hoses, etc.) and run RV antifreeze through it if that's your preferred way to winterize.

Just a note on the green antifreeze comment by Cory... My 09 MB with a PCM ZR409 came with the red coolant I assume like cars anything newer is going to have red. I am sure it really doesnt matter as long as whatever you top it off with is compatible though =-)

why does some of these systems have 2 thermostats?

Never seen one with 2 stats. The have 2 sending units.

The red anti-freeze is DexCool by prestone. Stick with it, don't change to green car coolant. According to my engine manual, car antifreeze conatins silicates which I'm guessing is bad. DexCool is ethylene glycol based and is better for anti corrosion.

When my exhaust heat exchangers were changed, there is a metal gasket between the riser and exhaust heat exchanger. This gasket prevents the raw water from entering the engine. Sooner or later the gasket fails and will need to be replaced due to normal operations.

Raw water does cool the anti-freeze. In my cooling system, there is a big tube where the coolant runs through a smaller tube inside the big tube to cool the anti-freeze. Follow the hoses and consult the engine manual for an idea. Don't have one, find the engine manufacturer website and search...

Thanks fellas I'll start digging around tomorrow and see what I can find. I have paper work on the boat since 2001, it was in Wisconsin. Not sure if it was in salt ever or not. How many people have closed cooling systems but have never been in salt or brakish? Anyone?

I sometimes ride in the CA Delta which in some parts more towards the Bay could be considered brackish, but I slip my boat on a fresh water lake so it rarely sees anything but that.

Nick.. Indmar? If so, I have the Clymer Manual that covers 1983-2003 Indmar... let me know if you wanna borrow it.

I forgot to ask you all about that. Do you have experience with closed cooling systems?

Red/pink antifreeze is HOAT (Hybrid organic acid technology) and not Dex-cool Dex-cool is orange. Dexcool is an OAT (organic acid technology) coolant. Green is ethylene glycol coolant and should never be mixed with HOAT or OAT it will make brown pudding in your coolant system. So-called universal coolants are propylene glycol often listed "as all makes all models". PCM engines call for Dex-cool, Mercury marine calls for ethylene gylcol. Indmar says to use Sierra Brand propylene glycol antifreeze.

Remember always use distilled water and not tap water.

Originally Posted by nick_in_ssp

How many people have closed cooling systems but have never been in salt or brakish? Anyone?

my '04 MB B52 had the closed system on its Zr6 engine, I would launch out of Suisun City,CA and take it near the Bay (Crocket,ca). But thats about as Brakish that it ever got...