I have a 4.3L Mercruiser engine and am having a problem with a coolant leak. The engine is a factory rebuilt I had installed about 9 months ago and the engine only has about 8 hours on it. The heat exchanger is the original. After sitting for several months I noticed the coolant level was down and it required a full container of antifreeze to fill it up. I have taken the boat out several times since and I have had to add about 1 1/2 quarts of coolant to maintain a full reservoir in the heat exchanger. The operating temperature of the engine appears normal. I haven't been able to find a leak in the water pump or in any of the hoses around the engine. The overflow tube from the heat exchanger does not discharge to a reservoir, so if the coolant is leaking out through that it would discharge to the bilge. I have not observed this while the engine is running. Any thoughts on the source of the leak and how to fix it? The cooling system seems fairly tight as it releases pressure when I remove the cap after not running it for a few days. I am fairly ignorant when it comes to fixing engine problems. Am I missing something obvious?
