I have A 97 F-150 4.6L triton 4x4,177,000 mi, It developed a very slow coolant leak coming from the passenger side head gasket, there is no water in the oil, however it seems to have some excess moisture coming from the exhaust while warming up,the motor has no other problems and still runs perfectly.

I really don't want to do a difficult head gasket job on a motor with such high mileage,when the time comes, I will probably just replace the long block,but at the present time it still runs as good as it did 100,000 miles ago and I'd like to be able to get another 50,000 miles out of it before its replaced.

After flushing the system out with water to add a block sealant, I noticed the leak did not occur with only water in the system, and there was less moisture coming from the exhaust when only water was used in the cooling system.

The block sealant did not work, and yes I followed the directions to the letter

Question: does the coolant have the ability to find its way through these pin holes where plain water cannot?,can I add something to water to keep it from corroding the engine besides coolant?

freezing is not an issue as I live coastal San Diego where if it ever gets below 40 we go out to the beach and sacrifice A goat.

 

The water just evaporates quicker.
I wouldn't run less the 40% antifreeze due to the fact that you have a cast iron block with aluminum heads and radiator. The electrolosis will make parts like the radiator and heater core prone to leaking. I also recommend distilled water, not tap water. The contaminants in tap water also cause electrolosis.