(This was a draft original written as part of a series of magazine articles; the project never got beyond draft form, and so here it is.)
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 your best 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 them from the fish, crab, or marine grass point of view. 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.
Glycerin has been suggested as a natural glycol substitute: don’t do it. Glycerin is as toxic to humans and mammals as EG, and 1000 times more toxic to marine organisms than other glycols. It is a poor antifreeze agent and is more difficult to rinse off. It does not dry.
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.
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.
Freeze/Burst Protection (data from Dow Chemical)
|
| Ethylene Glycol
| Propylene Glycol
|
| Freeze Protection (Vol.%)
| Burst Protection (Vol.%)
| Freeze Protection (Vol.%)
| Burst
Protection
(Vol. %)
|
20
| 16.5
| 11.5
| 18.5
| 12.5
|
10
| 26.0
| 17.5
| 30.0
| 20.5
|
0
| 34.5
| 23.0
| 37.5
| 25.5
|
-10
| 40.5
| 27.5
| 44.0
| 29.0
|
-20
| 46.0
| 29.3
| 48.0
| 31.0
|
-30
| 50.0
| 31.0
| 52.0
| 34.5
|
-40
| 54.5
| 31.0
| 56.5
| 36.5
|
-50
| 58.5
| 31.0
| 59.5
| 36.5
|
-60
| 62.2
Min. FP =
| 31.0
-62F
| 62.5
Min FP =
| 36.5
-63F
|
Vol. %
Proplyene 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 truck use, containing pre-charge of SCA (nitrite)
There is no reason to change closed cooling systems annually – they will last the recommended interval just fine. There is no reason to buy these from a marine supply house; you can find better deals through automotive and truck parts stores.
Disposal
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. 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.