I just purchased a new boat that had the closed cooled system on it and am not sure about impellar's. I was thinking it would still have one b/c it still brings water through the exhaust but not sure.

I can't swear to it, but I believe it does. It pumps raw water to the engine circulating pump and then through a heat exchanger to draw heat off of the coolant.

The way I understand it, the raw water pump pulls raw water from the through hull fitting and pumps it through a heat exchanger. The raw water is then dumped into the exhaust and exits the boat. The water pump in the block pumps antifreze through the block and through the heat exchanger. Your raw water impeller is now more important because you lose cooling efficiency going through a heat exchanger versus direct cooling.

Yes it should still have an impellar. Telling us your boat and engine/drive combo helps when posting. If you have a I/O then you definately will have a impellar to cool the drive also.

Your still using the lake water to cool the intake and exhaust manifolds. You should also be topping off your closed system prior to each usuage to ensure fluid level. I use 50% Distilled water and 50% Sierra coolant. Most set-ups have a bleeder line which spits out fluid so checking the level and topping off prior to usuage is a good habit to establish.

The recirculating part of the cooling system is essentially the same as the radiator in your car. Use the same antifreeze, treat it the same (flushes and changing the antifreeze). <BR> <BR>Instead of air to cool a radiator it uses water it pumps up from the lake/sea. This water is then dumped into the exhaust to cool it and to make it overboard. <BR> <BR>The pump/impeller issues are exactly the same as a "raw water" cooled system. <BR> <BR>Rod