Mixing Antifreeze and Water

George Van Parys

Mar 1, 2000
RO Number
There are some misconceptions in the service trade Regarding, the amount of antifreeze and water for protection in winter weather and sub-zero climates.

A mix of water and antifreeze EXCEEDING the 5050 ratio (say 7030) increases the freeze point protection down to -72 degrees F., but at the same time, it will reduce the cooling efficiency of the system. And, when the weather warms, such a 7030 mix could cause the Engine to overheat.
A blend of 5050 (water and antifreeze) brings protection down to -34 degrees F.
On the other hand, a 100 percent antifreeze solution (no water mixed in) has a freezing point of only 10 degrees F. above ZERO, it could turn to pure slush when outdoor temperatures drop lower than that.

This chart shows the reduced effectiveness of anti-freeze as the mix ratio changes.

One more bit of caution, Today's electronic engine control systems use a
TEMPERATURE SENSOR to send varying voltage strength signals to the on-board computer. With an improper mixture of antifreeze and water, the boiling point of the coolant will be changed. This simply means that the signals sent by the temperature sensor may be altered and cause a change in the calibration of the computer's output programmed control signals. A higher level of emissions is one result. Equally as important, if coolant in the system is below the correct "fill" level, the temperature sensor also will send out false signals and upset computer output commands.
The result of the low coolant level (especially electronically controlled engines) can also cause such problems as poor drive-ability, stalling, hesitation, poor fuel economy, and an increase in exhaust emission levels. Advise your customers of the important need for an annual cooling system inspection. Make them aware of how critical it is to maintain coolant at the proper level (and mix) all year! They'll never realize all of this unless you present the information at every face-to-face opportunity.

Adding Fresh Anti-freeze to Old Anti-freeze

You should be aware that adding new anti-freeze to very old anti-freeze can cause particulate matter ,suspended in the old anti-freeze, to precipitate out, and settle in areas of the block and heat exchangers. This particulate matter contains mostly rust, dirt, and the old anti-freeze itself, that has started to coagulate. This process can occur with relatively new anti-freeze that has been subjected to overheat or was originally mixed with high mineral content water. The bottom line is that it is safer to recommend anti-freeze replacement to your customers on a regular basis. Boats especially left in storage for long times should have their anti-freeze changed more often to reduce this type of settling.