I feel that it is time to change the coolant for the first time since I have owned the boat. The coolant that is presently in the 12 V 71 engines is a purple type colour and smells slightly of vinegar. Perhaps this is okay?? Regardless, what would be The simplest way to change out the coolant? The only way that I can see it happening is to drain all of the old coolant into the bilge and then suck it up? About 20 gallons per engine?