The Antifreeze Debate

Winter is here and for most boaters of the northern realms that means their boats are tucked away in storage for another season.  As temperatures dip below that magical 32° threshold there’s a certain ping of anxiety, an uncertainty as to whether or not an engine is enduring the hard freezes.  Water expands when frozen, and that simple truth means anything retaining water is subject to failure at sub freezing temps.  Even cast iron engine blocks are vulnerable to physics, and a freeze damaged block is often a several thousand dollar “oops”.  The solution? Winterizing.  A mythical operation to some, a normal chore to others.  Winterizing often includes the usual maintenance items: oil change, fuel conditioning, general inspection.  But, the primary purpose is to protect the raw water cooling system(s) from ice formation.  There are many different techniques to winterizing, but all can be arranged under two primary methods: Drying out the block or pickling with antifreeze.  This articles serves to distinguish between the two and demystify antifreeze’s role in winterizing.

Dry Draining

Dry draining a water system is the simplest winterizing method.  It involves draining all perceivable trapped water locations in the system.  Marine engine manufacturers include critical drain locations in a power system allowing proper drainage.  Other drain locations may include hose elbows and connections that must be disconnected.  Dry draining may also involve blowing out water circuits with compressed air.  Typical areas that must be blown out include water heaters and other auxiliary circuits connected to the engine.  After winterizing, drain locations and disconnected hoses are usually left open for the cold season to insure complete drainage.


Marine engine “Pickling”

“Pickling” an engine is the process of flushing the raw water system with antifreeze.  Antifreeze is either left in the system or selectively drained from major components.  The objective is to insure that the antifreeze is thoroughly mixed with any remaining water in the system and the antifreeze is concentrated enough to prevent ice from forming.

Antifreeze Types

Antifreeze comes in all varieties of combinations with an array of colors destined to bewilder the savviest of consumers.  The most well known is antifreeze coolant, the variety found in a vehicle’s radiator.  In a boat this antifreeze is used in “closed cooling” systems, also often referred to as “fresh water cooling” (not to be confused with raw water cooling!).  These systems are closed off to the external environment and remain in a closed loop circuit.  Antifreeze coolants are  manufacturer specific, and most are not environmentally  or health friendly.  These coolants are not used in winterizing procedures, but if equipped, should be checked for proper water/antifreeze ratio before cold weather lay-up.

The two varieties of antifreeze that are utilized for winterizing are RV antifreeze and Marine specific antifreeze.  While similar, these two antifreeze mixes are not the same and should not be confused with each other.

RV antifreeze:

RV antifreeze is often found as a pink mix adorning the aisle endcaps of local hardware stores.  Popular in… RVs (no way!), RV antifreeze is primarily intended for use in flushing out cold water systems prior to freezing weather.  Most are marketed as safe to use as intended and environmentally friendly.  The ingredients of the mysterious pink liquid are dependent upon the manufacturer but generally include propylene glycol, water, corrosion inhibitors, and other alcohols.  It’s inexpensive and readily available.  Common applications include live wells, potable water tanks, ballasts, and head plumbing.  It is not intended for engine block layup, though is often erroneously used as such.

Marine specific antifreeze:

Marine specific antifreeze is offered from several different marine suppliers and is intended specifically for marine power systems and engine winterizing.  It is marketed under many different names but consists mainly of undiluted propylene glycol and corrosion inhibitors.  Most chemical suppliers offering it in bulk will label it as “Inhibited Propylene Glycol”.  This antifreeze is often used at full strength in combustion engine water systems but may be diluted with water for some applications.


The Right Tool for the Job

Due to its availability and low cost, RV antifreeze is often thought to be a low cost alternative to marine specific antifreeze.  However, there are several key disadvantages to using RV antifreeze during engine layup.  First off is the concentration of propylene glycol in the mix, RV antifreeze is diluted with water and other alcohols to obtain a viscosity similar to water while still offering acceptable freeze protection.  This low viscosity allows RV antifreeze to flow easily through small pipes and water passages found in potable water systems, but comes at the cost of reduced efficacy in providing freeze protection in high capacity systems.  Undiluted proplyene glycol in marine specific antifreeze offers superior freeze protection when introduced to trapped water found in engine blocks.  The next concern with RV antifreeze is corrosion protection and reactivity in engine systems.  The concentration of corrosion inhibitors in RV antifreeze is often much less than marine specific antifreeze.  Marine specific antifreeze is formulated to provide maximum corrosion protection in iron and aluminum blocks.  This is a major concern in engines laying dormant in storage.  Corrosion inhibitors are required to act as a barrier between metals and the surrounding environment to prevent electrolysis and oxidation.  The added alcohols in RV antifreeze may also damage plastic, rubber, and aluminum engine components over time.  Ethanol is a common constituent of RV antifreeze, which is a strong enough solvent to slowly dissolve and “dry out” rubber and plastic hoses and impellers.

The final, but most often overlooked issue with using RV antifreeze is user safety.  RV antifreeze has a low enough flashpoint to poise a fire risk (albeit only under extreme conditions), but more importantly, some RV antifreeze mixes are not suitable for use above room temperature due to vapor toxicity.  Engine exhaust systems will quickly vaporize and disperse any antifreeze mix, this is of limited concern with propylene glycol which is considered GRAS (Generally Recognised as Safe) by the FDA and is not known as toxic is small quantities.  Other, unspecified alcohols found in RV antifreeze on the other hand, are certainly toxic when inhaled.  Regardless of the antifreeze used though, always insure sufficient ventilation when running a power boat in or out of the water.





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