Testing Coolant: Basic Question
 

I have a basic question related to testing my coolant.

My understanding is that coolant needs to do four things: transfer heat, prevent corrosion, not boil, and not freeze.

I have a basic hydrometer that tests only the freeze point. My question is: can I assume the the properties of a coolant, its abilities to do what it's supposed to do, deteriorate at approximately the same rate? So that, if the freeze point is still very low, I can assume that the boil point is still high and the corrosion prevention still intact.

Or conversely, is it possible that the deterioration of the properties will occur at significantly different rates?

Thanks.

antifreeze has little to do with the boiling point protection. the cap does that. higher pressure caps boil water at a higher boiling point.
PURE water will boil slower than water with antifreeze in it.
the water wetter products reduce the water particles and make it absorb heat faster... keeps the motor cool.

Hydrometer tests amound of dissolved stuff in coolant. Freeze and boil temps are dependant mostly on that. As vstech points out, pressure held by cap is predominant boil temp control.

Corrosion protection is via chems in antifreeze, and they get used up over time, hence the periodic repacement.

Expect corrosion protection to degrade nearly independently from hydrometer reading.

If I wanted to test corrosion protection, how would I do that? With one of those little strips?

A rule of thumb is that for every PSI an automotive cooling system is pressurised the boiling point temperature is increased by one degree Celsius...

Read more than you'd ever want to know about antifreeze here:-

http://en.wikipedia.org/wiki/Antifreeze

The manufacturers apparently have a different opinion. Zerex, for example, claims that a 50/50 mix of G-05 and water has a boiling point of 226 degrees F at standard atmospheric pressure.

That's an interesting claim, since 100% G-05 boils at 325 degrees F.

Water particle reduction. Now that's an interesting concept!!!

I believe he means that the anti-freeze reduces the hydrogen bonding between water molecules, which actually does reduce their size.

Generally the high boiling point of water and its high heat capacity is due to the hydrogen bonding between molecules. However, Tango, you are correct that the addition of antifreeze increases the boiling point of water. This is due to the colligative properties of mixtures and the fact that anti-freeze has a higher vapor pressure than water. The addition of anti-freeze increases the overall boiling point, despite reducing the hydrogen bonding of the water molecules.

I hope no one minds my geeking out here. http://www.peachparts.com/shopforum/images/icons/icon10.gif

Never Assume ANYthing WHEN :
 

The FSM tells how to check for corrosion protection of your coolant.

You use a VOM to check the corrosion protection ( as per the FSM )...

Incorrect. Freezing point depression and boiling point elevation are colligative properties and are solely due to the presence of other molecules/ions/atoms being dissolved in water. If you dissolve ANY substance in water it will both lower the freezing point and raise the boiling point.


Correct. The phase diagram of water (and every other substance I can think of) reveals that the boiling point increases with system pressure. The exact relationsip is described by the Clausius-Clapeyron equation.


"Wetter" water has surfactants present that lower the surface tension. This increases the efficiency of the heat transfer from the metal to the water.

Correct.

I am not aware of any product that will do this. Measuring the specific gravity with a hydrometer will not. You would need to identify what compounds are the corrosion inhibitors and then measure their concentration.

Incorrect. Hydrogen bonding is the major component of water's large heat capacity but does not explain the variation in boiling point (or freezing point) with the addition of anti-freeze.

Incorrect. Anti-freeze does not significantly alter hydrogen-bonding.

Incorrect. The size of these molecules size does not appreciable change because of the presence or absence of inter-molecular forces from other molecules.

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Interesting you should say that the addition of any substance would raise the boiling point - I'm under the impression that cavitation inception has been observed to occur more readily in mixtures or in the presence of foreign matter (often called dirt!) than for a "pure" liquid.

I don't believe I stated that the boiling point elevation was due to the hydrogen bonding of water or even an effect from the the hydrogen bonds, but did in fact state that it was due to addition of anti-freeze and therefore the colligative properties raising the boiling point.

Anti-freeze does significantly affect the hydrogen bonding of water as the surface tension of water is reduced upon the addition of anti-freeze. The surface tension is directly related to the hydrogen bonding of water and reduction in surface tension is a physical manifestation of the reduction in hydrogen bonding.

True in the sense of appreciable in a macro way. The original statement was made as a bit of a joke. However, at the atomic level there is "appreciable" bond stretch due to hydrogen bonds which does affect molecule size in an "appreciable" way at the atomic scale. But you are correct as far as molecule size in relation to the affects on a radiator and really as far as any of us are really concerned in most of our day to day lives.

You can buy a kit with test strips to test coolant, I keep them on-hand for testing. They are diesel-specific, the simple 3-way test: pH, Nitrates, and freeze-point, there are also 5-way strips.

The problem is that I don't know if these are accurate to the needs of a Mercedes-Benz automobile, so even if they indicate good there might be something that Mercedes diesels need that isn't being tested (or indicated to the proper Mercedes level). The kits only have about a 1-year shelf life, less than the life of the coolant in your car so if you do wish to play with the strips buy the 3-strip packet from NAPA instead of the more common 50-strip bottle$.

The easiest IMO is to just change at the factory interval with the proper G-05 coolant and distilled water (per FSM). On the 124s there is a new pressure tank available that has a silicate pack in it (aka: coolant filter in the H-D world) to extend the useful life of and stabilize the diesel coolant, I don't know if the same is available for your 126.

Yep. You can toss in sugar, salt, vinegar, etc and it will change boiling/freezing.

The "cavitation inception" I have heard of described as a nucleation source. That's why we put boiling chips in a beaker to control the boiling.

It is an entirely separate process than the colligative mechanism discussed above.

OK. Since I am fortunate enough to know something about this I tried to answer all issues. If I have misrepresented your thoughts I apologize.


I don't know that this is the place for this discussion but I'll try and see if it is useful.

I do not know how one would directly measure increased or decreased hydrogen bonding. I do not know if the IMF (inter-molecular force) of hydrogen-bonding (it's not a bond but an interaction) is measurable with spectroscopy. It's not an area that I have explored. So I am not aware of anyone showing an increase/decrease in hydrogen bonding by doing such-and-such.

Surface tension is a surface phenomena. It is understood by the presence or absence of certain chemicals that are at the surface. The term surfactant means surface active agent. It's very possible to add a chemical to water and have it present in the part per million level in the solution and yet be a thousand (or more) more concentrated at the surface.

I believe I understand the thinking of the statement: .. decreased surface tension indicates decreased hydrogen-bonding ...

It is not an accurate description of what is occurring. Sorry. It's not a personal attack I've just spent a lot of time studying inter-facial phenomena.


OK. An inaccurate explanation was offered. Sure did not seem to be a joke. I corrected it. My explanation allows someone to build upon it for greater knowledge in the future if they wish. Most other explanations that have been offered here will limit the ability to expand one's knowledge. Use the information as you choose.

That's interesting.

I wonder with the difference in AF composition today versus when the FSM was written if that is still valid.

Could you briefly describe the FSM procedure and values? Thanks.