Winterizing – glycol

Every fall I re-research which liquid to pour into my boats many freshwater systems. I find I keep coming back to  the blog by Practical Sailor author Drew Faye, Sail Delmarva.

I particularly like the fact he has researched his opinions and they are based on fact. So here are his winterizing suggestions:

    • Pump out the potable water tank. Vacuum out the remains with a shop vac.
    •   Add a shut-off valve and tee just down stream of the tank and upstream of the pressure pump. Add a second valve on the tee’s side branch and a length of 1/2-inch ID hose. Suck a 30% propylene glycol antifreeze mixture into all of the lines using the pressure pump, opening the taps one at a time (hot and cold) and letting them run; the clear water goes down the drain until it’s as pink as the feed (you can recycle some of this by boosting it with with concentrate). When finished, remove the suction hose from the antifreeze container and blow out the lines with the pump by letting it run dry for just 20 seconds per tap (the glycol lubricates the pump, so it will not be damaged in a minute). If you have a tank water heater you should drain it and bypass. I have an instant heater and the above works well.

  • Don’t leave the glycol in the system longer than needed. Don’t winterize until consistent light frost and break  winterization as soon as the frost leaves. Glycol is less inclined to go biologically active if it’s only in the boat when it’s cold. However, glycol is biodegradable and can turn into a nasty soup of bacteria and yeast if left in place in warm weather.
  • Don’t winterize with weak glycol.  Not only is freezing possible, but a nasty water system is a common result. If the glycol is stronger than 25% bacteria and yeast cannot grow; if it is less than 25% they thrive, feeding on the glycol like sugar.
  • Be careful which glycol you use. Neoprene and nylon don’t like PG. Best to leave nylon strainers off to drain. PG in potable systems, of course, but black water and engines  can be EG. Note that glycol for non-potable systems can be either propylene glycol (the pink stuff) or ethylene glycol (ordinary antifreeze) because both are essentially non-toxic to fish and to the sewage treatment plant.
  • Pump out the holding tank.
  • Pull the top off the head pump mechanism, lubricate the piston, and pour glycol into the chamber.
  • Remove the inlet hose from the head and hold it above the water line. Open the sea cock and pour enough glycol in the hose for it to back flow out the sea cock. Close the sea cock.  Replace the hose on the head inlet. Alternatively, install valves so that you can simply suck glycol into the head. Do remember that pouring glycol into the bowl does not winterize the intake side.
  • Flush the head with a 15-20% glycol mixture until March. Place a gallon jug in the head compartment labeled “for flushing only” filled with this glycol mixture.  This will keep the holding hank, discharge side of the pump and the bowl freeze-proof.
  • Keep the gasoline tank full. Actually, this is my practice all year long to reduce moisture absorption into the e-10 gasoline and to prevent separation, all the more important the winter, because e-10 separation is primarily triggered by low temperatures. See the EPA document to this effect ( Alternatively, consider a silca gel vent filter.

I did a variant on this. Drained the water tank via the valve I installed just before the filter at the pump. Then I pumped air through the system, drained the hot water tank (that was murky with scale!) and then pumped it full of antifreeze. Finally I reversed the water pump and drained the antifreeze out of the system. My logic is that if there is any liquid still in the pipes it will be antifreeze and the small quantity should reduce any freeze burst as well. It also means I can reuse the antifreeze to winterize the engine. I’ve kept a full strength jug avail to go into the engine last in case the antifreeze is a bit diluted.

I looked inside the water tank and there is but a tiny amout of water on the bottom, a small puddle about 1/8″.  I figure this won’t do any damage… fingers crossed.


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