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pH spent coolant? #4035907 03/11/16 08:56 PM
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deoxy4 Offline OP
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I work in a lab and have the opportunity to check the ph of my coolant. An acidic pH is one indicator of spent coolant, as it has lost its ability to buffer.

Honda 50:50 coolant has a pH of 7.9 according to Honda MSDS. I follow Honda's recommendation for coolant change which is 5 years/60,000 miles after the initial factory change. I haven't experienced a problem. However, I would like to measure the pH of the coolant, pre-summer and pre-winter, to give myself a little peace of mind. I would also check the specific gravity with one of those inexpensive testers. I am not that concerned to send out a sample for analysis.

A pH of 7 is neutral and in need of change but at what pH is coolant spent?

Re: pH spent coolant? [Re: deoxy4] #4035912 03/11/16 09:02 PM
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abycat Offline
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depends on the coolant. you would have to measure the ph in the same coolant but brand new. thats the only thing needed to establish trends and any kind of data. also make sure all the coolants tested are the same temperature for accurate results.


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Re: pH spent coolant? [Re: deoxy4] #4035923 03/11/16 09:10 PM
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deoxy4 Offline OP
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pH of Honda type II coolant is from their Material Safety Data Sheet, so that would be "new" coolant being 7.9.

Samples would be at ambient temperature which I would assume that Material Safety Data Sheet testing would imply.

Re: pH spent coolant? [Re: deoxy4] #4035927 03/11/16 09:13 PM
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deoxy4 Offline OP
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Here is some information that I was able to find from a machinery maintenance site.

In general, coolants degrade over time as the ethylene glycol breaks down into primarily glycolic and formic acids. Degradation occurs more quickly in engines operating at higher temperatures or those that allow more air into cooling systems. The coolant should be tested on an annual basis if it is intended to operate the system for several years between coolant changes, and particularly where the coolant is used in severe applications. One test ensures the pH is still above 7.0. Some coolant technologies can protect as low as pH 6.5, however, it is typically not good practice to allow a coolant to operate below a pH of 7.0. Glycol breakdown products are acidic and contribute to a drop in pH. Once a coolant has degraded, due to glycol breakdown and pH drop, engine metals are at risk for corrosion. Coolant degradation can be slowed by using coolants with extended life inhibitors and by ensuring that the equipment is operating correctly and within designated design limits.

It appears that they feel that a coolant change would be necessary at a ph of 7.0 or below.

Re: pH spent coolant? [Re: deoxy4] #4035956 03/11/16 09:37 PM
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Makes sense. Anything into the acidic range might start eating into the cooling system. However slowly.


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Re: pH spent coolant? [Re: deoxy4] #4035977 03/11/16 10:12 PM
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Newer Hondas have a much longer interval, which can be over 100k when done according to the MM. What is the pH of Type II with 100k on it?

Re: pH spent coolant? [Re: Colt45ws] #4035978 03/11/16 10:14 PM
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Makeup water systems for boilers are typically kept in a pH range of 8-9. Boiler chemistry itself is usually inside the range of 8.4-10.6 depending on pressure and amount of additives.

From what I can find coolant pH is similar. Optimum would be in the 9.0-10.5 range. Straight demin water is approx 6.5-7.0 while straight anti-freeze is up around 10.5+. Another factor of coolant age is the electro-chemical reaction current flow or electrolysis. Apparently DexCool and other LL/PG coolants run at a lower pH than EG.


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Re: pH spent coolant? [Re: deoxy4] #4035986 03/11/16 10:30 PM
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Dexcool is still EG, not PG.


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Re: pH spent coolant? [Re: deoxy4] #4036001 03/11/16 11:12 PM
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deoxy4 Offline OP
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Honda Type II coolant is ethylene glycol based and is pH 7.9 according to their MSDS.

Re: pH spent coolant? [Re: 69GTX] #4036173 03/12/16 08:33 AM
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I wonder if RMI contains something quite basic (in the chemical sense) that increases pH?

Re: pH spent coolant? [Re: deoxy4] #4036212 03/12/16 09:31 AM
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This is just a thought. Let me know what you think. I add 1/2 TSP of baking soda to a gallon of R/O water I keep in the fridge. It raises the pH from 7 to around 8. I find that drinking this instead of the straight R/O water reduces my heartburn a bit. Do you think that adding a similar amount of baking soda to R/O or distilled water prior to mixing with coolant would be beneficial in any way? It does dissolve completely and I have never seen any precipitate in the bottom of my refrigerator jug.

Re: pH spent coolant? [Re: deoxy4] #4036226 03/12/16 09:45 AM
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Well it is going to be "spent" when the pH changes from what the buffer attempts to hold it at. But by then it is too late of course as the pH will change rapidly from then on.

I don't know specifically how coolant is buffered but I would think that to get a sense of the remaining life (in regards to the buffers at least) one would want to titrate a sample and compare that to what you get with virgin coolant. pH is just the current status of the coolant and doesn't tell you what the remaining ability of the coolant is to neutralize acid.

Specific gravity only shows concentration as I'm sure you know, and that shouldn't change from when it is originally mixed unless you are adding water or something.

Originally Posted By: deoxy4
I work in a lab and have the opportunity to check the ph of my coolant. An acidic pH is one indicator of spent coolant, as it has lost its ability to buffer.

Honda 50:50 coolant has a pH of 7.9 according to Honda MSDS. I follow Honda's recommendation for coolant change which is 5 years/60,000 miles after the initial factory change. I haven't experienced a problem. However, I would like to measure the pH of the coolant, pre-summer and pre-winter, to give myself a little peace of mind. I would also check the specific gravity with one of those inexpensive testers. I am not that concerned to send out a sample for analysis.

A pH of 7 is neutral and in need of change but at what pH is coolant spent?


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Re: pH spent coolant? [Re: abycat] #4036242 03/12/16 10:03 AM
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Originally Posted By: abycat
depends on the coolant. you would have to measure the ph in the same coolant but brand new. thats the only thing needed to establish trends and any kind of data.


You would want to titrate it, unless all you want to know is when it has already lost its ability to buffer.


1994 BMW 530i, 253K
1996 Honda Accord, 289K
1999 Toyota Sienna, 437K
2000 Toyota ECHO, 290K
Re: pH spent coolant? [Re: DBMaster] #4036436 03/12/16 02:06 PM
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deoxy4 Offline OP
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Originally Posted By: DBMaster
This is just a thought. Let me know what you think. I add 1/2 TSP of baking soda to a gallon of R/O water I keep in the fridge. It raises the pH from 7 to around 8. I find that drinking this instead of the straight R/O water reduces my heartburn a bit. Do you think that adding a similar amount of baking soda to R/O or distilled water prior to mixing with coolant would be beneficial in any way? It does dissolve completely and I have never seen any precipitate in the bottom of my refrigerator jug.


May well have an effect. Honda's coolant is primarily ethylene glycol, potassium hydroxide, and some inorganic and organic acid salts probably used as extended life inhibitors. Water chemistry and coolant chemistry may be different animals. I don't know if it would be a good idea to mess with their designed chemistry.

Re: pH spent coolant? [Re: deoxy4] #4036452 03/12/16 02:34 PM
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kschachn Offline
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Originally Posted By: deoxy4
May well have an effect. Honda's coolant is primarily ethylene glycol, potassium hydroxide, and some inorganic and organic acid salts probably used as extended life inhibitors. Water chemistry and coolant chemistry may be different animals. I don't know if it would be a good idea to mess with their designed chemistry.


Well the coolant in the car is about half water so the effect is going to be the same.


1994 BMW 530i, 253K
1996 Honda Accord, 289K
1999 Toyota Sienna, 437K
2000 Toyota ECHO, 290K
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