Choosing the Right Antifreeze/Coolant: What’s a Technician to Do?

October 30, 2015 | Reply More

Antifreeze seems to come in all colors of the rainbow these days.

Which one is right for BMWs?

EG (%)
(deg F)
(deg C)
0 32 0
10 25 -4
20 20 -7
30 5 -15
40 -10 -23
50 -30 -34
60 -55 -48
70 -60 -51
80 -50 -45
90 -20 -29
100 10 -12
Ethylene glycol freezing point
vs. concentration in water

To be precise, the liquid you pour into a radiator should be referred to as “antifreeze/summer coolant” because it not only keeps the icebergs away in winter, but also helps prevent boilover in summer. In addition, antifreeze contains an additive package that protects against corrosion and degradation of aluminum, steel, and iron components that are wetted by the coolant. Most brands and types of antifreeze on the market today are based on ethylene glycol (more on this later…).

It is interesting to note that these various ethylene glycol solutions continue to lower the freezing point down to about -60 deg. F., with a concentration of 70% antifreeze, 30% water. Beyond a concentration of 70%, the freezing point of the coolant actually rises, with pure ethylene glycol antifreeze freezing at about 10 deg. F.

On the other hand, the boiling point of a solution of ethylene glycol antifreeze continues to rise with the concentration of the antifreeze, with pure ethylene glycol boiling at about 387 deg. F.

And consider this: each pound of pressurization in a cooling system raises the boiling point by about three deg. F. So a ten-pound pressure cap will raise the boiling point of pure water to about 242 deg. F. And that same pressure cap used with a 50/50 mixture of antifreeze and water will yield a boiling point of about 255 deg. F., which can spell the difference between comfortable motoring on a hot summer day, or a boilover by the side of the road.

It All Started With Alcohol

EG (%)
(deg F)
(dec C)
0 212 100
10 215 102
20 215 102
30 220 104
40 220 104
50 225 107
60 230 110
70 240 116
80 255 124
90 285 140
100 387 197
Ethylene glycol boiling point
vs. concentration in water

As recently as the 1950s, automotive antifreeze was alcohol-based. Formulations of the day prevented freeze-ups, but presented several shortcomings. They lacked the additives that have become so important in more modern cooling systems, and the alcohol tended to boil off and vaporize, resulting in less protection against freezing, and bringing the need for frequent replenishment in order to restore freeze-up protection.

So, in that long-ago era chemists came up with blends based on ethylene glycol, which has become the basis of nearly all antifreezes since. These products, in a typical 50/50 mixture with water, provide freeze-up protection to about -34 deg. F. The 50/50 mixture is a convenient number to remember, and ethylene glycol is not subject to the evaporation that


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Category: Cooling Systems, the bimmer pub

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