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Selecting Antifreeze


The chemical in antifreeze that resists freezing is either ethylene glycol (EG) or propylene glycol (PG). Ethylene glycol makes a good antifreeze/coolant, but it’s a poison that’s deadly to pets and wildlife and makes disposal problematic. Propylene glycol is odorless, tasteless, biodegradable, and nontoxic. While it is slightly more expensive to produce, it offers a combination of safety and effectiveness we feel makes it a superior choice for marine use.

Antifreeze applications

The three main applications for antifreeze are potable water systems, winterizing non-running engines, and engine antifreeze-coolants.

  • Potable (drinking) water systems require a completely non-toxic antifreeze that has no harsh chemicals. Our Pure Oceans Antifreezes are ideal.
  • Boats laid up for the winter need freeze and corrosion protection for their engine cooling system, but they don’t need the stabilizing chemicals that are added to antifreeze/coolant to protect the engine from breakdown of anti-corrosion additives at high operating temperatures. For winter lay-up, our Pure Oceans -50, -60, and -100 Antifreezes are formulated to provide safe, effective protection for non-running (stored) engines.
  • Our Pure Oceans Engine Antifreeze and Coolant is ideal for all engine uses and can be used as a coolant in the summer, and for antifreeze protection (for your boat’s engine only, not for the water or waste systems) in the winter. You can find it in the Engine section of this site.

No matter what type of antifreeze you choose, be sure to follow the manufacturer’s dilution ratio instructions carefully. When buying antifreeze, you are mostly paying for ethylene or propylene glycol, the proportion of which can vary from 25 to 95 percent. That’s why lower temperature rated products are more expensive. Products that advertise protection to -50°F may require that you use the product full strength, while other products can be diluted with water at a 3:1 ratio and provide the same -50°F protection. Shop carefully and remember that cheapest isn’t always the best value!

For more technical info about understanding burst point and freeze point, and about our West Marine Antifreeze, click on the link at the bottom of this article.

Selection Chart for Pure Oceans and Seafit Antifreeze

  PG Percent Burst Rating Freeze Rating
Seafit -50° Antifreeze 28% -50°F +14° to +18°F
Pure Oceans -50 30% -50°F +12° to +16°F
Pure Oceans -60 35% -60°F +7° to +10°F
Pure Oceans -100 60% -100°F -58° to -63°F
Pure Oceans -200 96% -200°F -98° to -103°F