Types of Antifreeze for your boat by Simon Phillips

There are two main types of antifreeze which can be found on the market, one is highly toxic and the other is not!

Being onboard a yacht and surrounded by wildlife – one of the main draws for sailing, it would therefore be considerate to choose the more environmentally friendly type!

The chemicals in antifreeze that resist freezing is either Ethylene Glycol (EG) or Propylene Glycol (PG).

Ethylene Glycol makes a good antifreeze/coolant, however it is poisonous and deadly to pets and wildlife. The other issue with this is that it is difficult to dispose of in a correct manner.

Propylene Glycol has the benefits of being odourless, tasteless, biodegradable, and nontoxic. Even though it is slightly more expensive
, it offers a combination of safety to the environment and retains effectiveness at providing the security that an antifreeze should.

It is for these reasons, that one should use Propylene Glycol rather than Ethylene Glycol.


The purpose of Antifreeze

The main purpose for antifreeze would be to prevent freezing in the water systems onboard, the sanitation systems and engines.

  • The water system
    onboard should be winterised with a completely non-toxic antifreeze that has no harsh chemicals.
  • Boats which are laid-up for the winter should have corrosion and freezing protection for their engine’s cooling system added before the chance of freezing – now!


Regardless of the type of antifreeze you use, follow the manufacturer’s dilution ratio instructions carefully. Most of the cost of antifreeze is for the ethylene or propylene glycol, the proportion of which can vary from 25% to 95%. Therefore, lower temperature rated products cost more. Products that advertise protection to -20° 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 -20° protection. Be cognisant of this when choosing antifreeze, as always – the cheapest is not the best!