A Marine Winterizing, Antifreeze, and Engine Coolant Primer

rev 3-2-2010
rev. 12-16-2015
rev. 9-20-2016

Protecting marine water systems from ice damage is the simplest of aims, but the terms and product claims are confusing. A little education goes a long way. Yup, you can blow the system out with air or drain it; that is not the topic I am speaking to today.

Toxicity

For the potable water systems on a boat there is only one reasonable alternative: propylene glycol (PG), the active ingredient in virtually all marine and RV antifreeze products. Identified by the FDA as “generally recognized as safe” it has very low toxicity to people and mammals and no identified long-term health effects at modest doses. It can be used in toothpaste and foods; over 1 pint/170 pounds is required to be fatal. Ethylene glycol (EG), commonly used in automotive engine coolant, is toxic to people and mammals when ingested; less than ½ cup per 170 pounds is expected to be fatal. Neither is carcinogenic or causes any adverse health effects at incidental exposure levels. Both glycols have a sweet taste. Material Safety Data Sheets (MSDS) are a convenient source of information, widely available on the internet.

Marine toxicity is a different matter; both ethylene glycol and propylene glycol are low in toxicity, and there is no established difference between for fish, crabs, or marine grass. Toxic effects require 4-20% of either glycol—levels which cannot be approached with small spills because of immediate dilution.  Biodegradability is also equal; both are as easily degraded as food wastes. Claims that propylene glycol is more biodegradable or friendly to the marine environment are offered without relevant basis or back-up; we have searched high and low—the research says they are the same. See http://www.riskworld.com/Abstract/1996/sraeurop/ab6ad040.htm and MSDS information.Thus, for engine and head antifreeze, there is no strong reason to prefer PG over EG.

http://www.sciencelab.com/msds.php?msdsId=9927239 EG MSDS

http://www.sciencelab.com/msds.php?msdsId=9927167 PG MSDS

Glycerin has been suggested as a natural glycol substitute: don’t do it. It is a poor antifreeze agent, is more difficult to rinse off, does not dry, and gets very thick in cold weather. Glycerine is also more toxic than generally understood; better than ethylene glycol, but twice that of propylene glycol. Drugstore glycerine bottles now carry a warning against excessive use on baby's skin. Not all "natural" products are safe.

• Ethylene glycol, rat oral, 4,700 mg/kg
• Glycerine, rat, oral, 12,600 mg/kg
• Proplyene glycol, rat oral, 25,000 mg/kg 

Unavoidably, some glycol will find its way back into the water after launching. Try to minimize this loss; both are pollutants and both lower dissolved oxygen levels when they degrade. 

Why does this matter?

Compatibility
            Not all materials like polypropylene glycol. The rubber parts (neoprene) in water pumps (impellers) and heads (joker valves and o-rings) are stiffened by PG. Even worse, some plastics, notably polyamide (nylon) strainers can craze and fail. The strainer below was ruined in just two seasons. Because it is in the fresh water system where I must use PG for safety, I now simply leave it out for the winter, but I cringe at the materials I don't know about. However, it is this sort of materials compatibility issues that has completely blocked PG from OEM engine coolants. You can buy them in the aftermarket, sold under the false claim that they are better for the environment. However, they are not good for the car and using them is a risk.

Burst Point

A fuzzy term without ASTM or other industry accepted standard test. It is generally recognized as the temperature where the entire mixture has become solid, though expansion may begin before this. Strong and tough materials (steel pipe) resist the strain of expanding ice better than weak and brittle materials (cast iron and PVC), and yet manufacturers of RV antifreeze seem to be “optimistic” when compared to major glycol producers’ data.

The freeze point has an ASTM recognized definition and test method; it is the temperature where the first ice crystals form. Automobiles and any system that is to be operated in cold temperatures must be protected to the freeze point to insure reliable pumping with no ice crystal present. 

As for those materials that claim -100F or -200F burst point material, there is no science to support it; all EG and PG mixtures freeze solid before -65F is reached. This is lying, plain and simple; notice that DOW does not make such silly claims. Educated industrial buyers know better.

Another word of caution for those that would use the minimum amount; when antifreeze is subjected to freeze/thaw cycling, the ice crystals float, and the glycol rich solution sinks. There will be some separation, and the burst point at the top of a complex pipe system can be much greater that the predicted value. This is common in large, complex piping systems.
Fermentation is a concern if less than 25% (that -50F burst point stuff) is used. With just a few bacteria or yeast and a little warm weather before launching, weak glycol can turn into a repulsive mixture, reminiscent of a half bottle of Thunderbird found under the seat of a used car. Sailors complain about the taste the glycol leaves behind--most often it is the fermentation products they are tasting, not the glycol. Fermented glycol also becomes very acidic and corrosive, with a pH of <5 .="" 25="" air="" alcohol="" an="" and="" as="" been="" brandy="" by="" commercial-scale="" conditioning="" dow="" extensively="" fermentation="" has="" if="" important="" in="" inhibited.="" is="" it="" like="" others="" over="" p="" problem="" studied="" systems.="" this="" used="">

The glycol content of a product is best measured with a refractometer calibrated for the glycol used. Most can test EG, PG, and battery acid—very handy—and are available for about $50. No mechanic should be without one. Glycol content is also listed on manufacturer supplied MSDS sheets, though it is conspicuously absent from packaging labels. Very curious indeed. Please note the price information below is VERY market dependent. Winter 2008 was high, Winter 2009 is much lower and I have not up-dated the table.

                                                Vol. %                   

                                                Propylene    Freeze    Burst  Price (2008)

Product                                  Glycol           Point, F   Point, F    $/lb PG

***Camco Ban Frost 2000     97                  -60           -60         $1.85

Camco Freeze Ban -100          64                  -63           -63         $1.89

Camco Freeze Ban -50            32                    5            -25         $3.84

*Star-brite -200 RV / Marine  97                   -60          -45         drums only                  

Star-brite -100 RV / Marine    60                   -60          -60         $2.45

Star-brite -60 RV / Marine      32                    5            -25         $2.49

Star-brite -50 RV / Marine      25                   10            0            $2.37

Sea-farer -50 Marine               25                   10            0            $1.90

* Concentrate. Use at 30-60% to get freeze point of -10F to -60F.

* * Product names do not always match always burst point claims, as determined from MSDS glycol concentrations and test data.

***For engine use only. Not for potable water systems. Like EG engine coolants it contains corrosion inhibitors with some toxicity.

Engine Coolant

Most RV (propylene glycol) antifreeze products are not designed for use in operating engines, and they are not optimized for corrosion protection. They contain only small amounts of corrosion inhibitors, and not the additives required in engine coolants; those additives are too toxic for potable water systems. There is no such thing as a “marine” engine coolant, in the sense that it is formulated specifically for or is better for marine applications; automobile and truck manufacturers have research this subject since the beginning of engines, and you should chose according to the engine type you have:

Gasoline or light-duty (not wet sleeve liners) diesel engine

PG or EG engine coolant                    *  Long-life type, 5 yr., typically yellow or red.

                                                              *  Conventional type, typically green.

Heavy-duty (wet sleeve liners) diesel engine

PG or EG engine coolant                    *  Long-life type, 5 yr., typically yellow or red.

                                                             *  Conventional type, typically green or pink.
                                                      Both must be rated for diesel (heavy duty) use. Some contain an SCA pre-charge of nitrite, while many of the newer formulations are nitrite-free. Nitrite-free has certain advantages for road use (nitrite can form ammonia in situ in certain brazed aluminum heat exchangers) but this makes little difference in marine engines.

Change interval. The coolant interval ratings are stated above. However, in marine applications the conventional wisdom is to change the coolant every 2 years, because of the risk of seawater contamination (0.2% is the condemning limit based upon chloride) due to heat exchanger internal leakage. Seawater is about 25,000 ppm chloride, and is also high in sufate and hardness.

(water requirements from ASTM D3306)
Contaminatant in Water                     Maximum PPM
Chloride                                                  25             
Sulfate                                                     50             
Hardness                                                 20             

   

Disposal
(I designed and built this plant in 1995. Chemical engineer by training.))

Recycling is always best, and because of the high value of glycols, used antifreeze has a value to recyclers. Both propylene and ethylene glycol are recyclable, and they can be commingled in collection tanks at your marina, county collection center, or service station. The best recyclers distil the spent antifreeze under vacuum and produce glycols and coolant products meeting all virgin engine coolant specifications; much of the recycled product finds its way back into the cars you drive as factory fill!

Bottom Line

• Buy antifreeze by the pound of glycol. In 2008, Camco -100 for water systems and Camco Ban Frost 2000 for engines are the best deals; several others are very close, but Camco -100 has the safety factor to handle water left behind.
• If your engine has a glycol cooling system, buy at the auto or truck parts store, either EG or PG. Long-life formulas are cheaper over time, though they should not generally be mixed with or used to replace conventional green antifreeze; there can be compatibility problems. The new “global” or universal” products have solved most of these issue. However, remember diesels should get diesel engine coolants; that peculiar diesel rattle produces vibrations and cavitation corrosion that automotive coolants cannot protect against.
• Be wary of skimping; freeze/thaw cycling separates glycol/water mixtures and can cause bursting of complex systems and horrible fermentation problems. Be cautious with weaker products if there is any water remaining in the system. PG concentrations in the system of less than 34% are questionable at low very temperatures—the burst point curve is very steep in that range.