Coolant vs Water

In the summer when the tempertures reach into the 90"s will it hurt your car to put 100% antifreeze and no water in the cooling system? In the summer will it harm your car to put 100% water in your cooling system and no antifreeze? Why do they recommend that you use a 50/50 mix?

The properties of the 50/50 mixture are superior to those of pure water or pure antifreeze. Use the 50/50 mix.

Read the back of the antifreeze bottle. That will give you the optimum mix for your driving environment.

[b]Using 100% antifreeze at anytime has two drawbacks.

Antifreeze by itself is a poor heat tranfer medium.

Antifreeze by itself can gell in a cooling system.

Using 100% water at anytime has three drawbacks.

Water by itself has a lower boiling point.

Water by itself has no lubricating properties for the water pump bearing.

Water by itself has no anti-corrosion properties.


Using 100% water at anytime has three drawbacks.

I may be wrong, but I believe it also has less ability to carry and transfer heat than the mix.

I don’t think that any other fluid (under practical conditions) has better heat transfer properties than water. Glycol and water/glycol mixes definitely do not.

I say under practical conditions because melted metals (i.e… sodium) can probably transfer heat better and there may be fluids that transfer heat better if they are under very high pressure or at very low temperatures.

The problem with pure water is the high surface tension. Products like glycol based coolants and surfactants reduce the surface tension of the mixture and so reduce the potential for localized boiling.

Yes, you will be in a lot of trouble if you try to use 100% water in summer, and even worse trouble using 100% antifreeze in winter.

You have gotten posts about the thermal conductivity of water, its surface tension, lack of anti-corrosion inhibitors, and so on. All of it is true. But those concepts are not what really matter.

The 50/50 mix raises the mixture’s boiling point. Pure water boils at 212F (100C) which is too low for your engine. Use it and your car will overheat, blowing steam out the pressure cap. In addition, steam inside your engine is ineffective in drawing off the heat. You may cook your engine.

The 50/50 mix lowers the freezing point to about -40F or C. Pure antifreeze freezes at a higher temperature. On a cold winter’s day it might well freeze and crack your engine block, whereas those cars with a proper mixture will still have liquid antifreeze in their veins.

That’s what really matters!

What is the boiling point of a 50/50 mix if pure water is the usual 100 C?

OK, you made me go look it up. Here are the numbers.

Pure water boils at 212F (100C) at normal atmospheric pressure.

A 50/50 mixture boils at 227F (108C) at normal pressure.

But a cooling system is pressurized. So assuming an additional 15 psi in the closed cooling system we have these figures:

Pure water boils at 250F (121C).
The 50/50 mix boils at 265F (129C).

Incidentally, pure antifreeze freezes at -5F (-21C) so you can see you would not have much cold-weather protection with straight antifreeze.

(The above data apply to ethylene glycol-based antifreeze, the “green stuff.” They may not apply to other types.)

Pure water is magnetic, that is the individual molecules have north and south poles, for this reason it has a high surface tension and therefore is not optimized for heat transfer. Adding a small amount of antifreeze reduces this tension and increases its ability for heat transfer. My understanding is that from there, its abilities decrease with increasing concentration, but not that much. I prefer a 2:1 mixture, 2 parts antifreeze to 1 part distilled water. I like to get in all the corrosion protection I can.

As others have pointed out a 50/50 mix of anti-freeze and water has a lower freezing temperature than either one alone.

Water has better heat transfer characteristics than the mixture, but not all that much better, so if you live where it ever gets below 32F you should have anti-freeze in the system. There are products for sale in places like Florida that you can add to plain water to get the lubricants and anti-corrosion components without the anti-freeze but, seriously, what is the point? Regular anti-freeze is pretty cheap.

Water is not “magnetic”, but polar.

Each molecule has a north and south pole, that makes it magnetic.

As others have pointed out a 50/50 mix of anti-freeze and water has a lower freezing temperature than either one alone.

I don’t know how you would support this contention. Maybe its true, but back in the 60’s and I live in So Cal and the engines were cast iron, I found by experience on several vehicles that they would overheat on pure water on occasions, but never did with a little antifreeze in the mix. I didn’t go 50/50 back then, usually just a quart or two in a two gallon cooling system. Didn’t have to worry about freezing then. My last vehicle like that was a 66 Dodge with a B block. I used 50/50 on it (moved to Tennessee) and it never overheated, even when idling for 45 min in a parking lot with ac on full on a 100?+ day.

Um, I ignored your mistake the first time since it is so unimportant, but give Beads his due. A water molecule has an elecrically positive pole and an electrically negative pole. That makes the molecule polar, not magnetic.

None of this matters to our discussion of antifreeze so let’s just move on.

A water molecule has a magnetic field as well, that makes it magnetic.