The 5 gallon bucket I use for PG antifreeze has been graduated with a Sharpie marker at each gallon. This makes it easy for me to stop pumping, take a concentration measurement, and then continue. In the end I know exactly how many gallons it took to get the right concentration into the system, no more, no less.. In this image the bucket has exactly 1 gallon in it...


Each of the boats I winterize has a winterizing info sheet derived from the first winterizing I conduct on the vessel. The engine & domestic water systems are tested for concentration/freeze point with a sight refractometer to determine exactly how many gallons it takes to properly protect the system and reach the undiluted point. The next year I pull the winterize sheet up on my computer or iPad and know exactly how many gallons is required for the engine and how gallons for domestic water. This step avoids guessing and waste.


Remember a refractomer is measuring the PG's "freeze point" not the burst point. Don't be alarmed if a sample straight from the bottom reads 7F - 10F. What comes out the taps or engine exhaust should ALWAYS match a sample straight from a virgin bottle of the AF you are using. In other words if your West Marine Pure Oceans -50F reads 8F then what comes out of the taps or engine should also read 8F.