FredR

Just preparing for my annual inspection/maintenance programme that I usually tackle around mid Feb. I typically replace the coolant after two years but I have long suspected that may be a tad conservative.

I was at my good friends home the other day and whilst there he was working on his aquarium. I noticed that he took a test strip out of a tube and dipped it in the water for a second and then read the colours on it. Asked him what he was doing and amongst several parameters it read pH. I immediately figured it might be useful to test my coolant pH so he gave me a couple of these test strips. Dunked the thing in my coolant after I got home and it turned reddish indicative of a pH of 8.4. Thus I reasoned no need to change the coolant as it is past its sell by date if the pH goes acidic. So, the makers recommendation of changing it after 3 years or many more miles than I will ever cover may well be valid.

Any thoughts on the pH test?

I would upload a pic but I am having some difficulty posting pics for whatever reason- any suggestions regarding that appreciated

77tony

Fred, Great idea^^. I've had good luck bumping down the text a few lines, then clicking onto "Go Advanced", then bumping down the text again a bit, then adding pics. T

FredR

Tony,

Tried the tip regarding posting the pic but no joy.

dr bob

Fred --

Min pH recommendations vary based on the type of coolant you are using. Some OAT coolants in aluminum deserve higher pH, for instance. IIRC the number I look for with the Zerex GO-5 is north of 8.5 or so. Some look for >9. A little research on your particular coolant will provide specific guidance.

FredR

Bob,

My thinking is based on the titration curve we learned about in school- one or two drops can turn a solution from alkali to acidic [and vice versa] thus if this technique suggests the coolant is alkali [as it does] then it should be good to go as it were. On the other hand it could flip tomorrow for all I know so it would be prudent to monitor the condition of the coolant on a regular basis [once a month?] until such time as I can get a feel for when it goes south. The good news is that I can confirm that after two years of service the coolant is still viable. Taking this approach one might be able to better determine an appropriate change interval for one's user profile.

Hey_Allen

Some auto parts stores have coolant test strips, that test for the corrosion inhibitor package (in certain types of coolant.)
I learned about this from my father who is a fleet mechanic for the state of Oregon. Instead of changing the coolant in all 60 vehicles on a bi-yearly basis, they test using the strips, and dose it with the coolant supplement as needed.

dr bob

I keep the test strips and have a cool little pH meter. I test the coolant, and it's still showing 9+ when I change it every couple years. My rationale is that coolant is cheap, it's easy to change, and running it to the point where there's any risk of corrosion is running it too long. Many of us have seen the devastating effects of tired coolant on the radiator, block, and the heads. Considering there's no easy recovery path for loss of aluminum in the system, my habits tend towards the conservative. Lots of the stuff I do is overkill, but I also plan for the car to stay in great condition for at least another thirty years or so.

---

Visiting a neighbor to fix some garage door issues, her derelict son's BMW 850 coupe takes up one of her three garage slots. It's the 12cyl version, in black/black and filthy in and out. It's untouched in years, save for the battery maintainer connected. Would be an interesting project except for the hidden damage that neglect allows. Kinda like a yard-find 928, or even a garage queen that's never needed service because it's never driven. Or the edge of a baby diaper, waiting for that first peek-and-sniff under the edge. I hate to see beautiful pieces of engineering art neglected and lost to the scourges of corrosion.

Bertrand Daoust

What's the pH on new coolant?

Would be interesting to compare.

worf928

M. Requin

And so off to Amazon, to get a "cool little pH meter", and then some extra buffer solution chemicals, and then - oh why not - a "cool little" refractomer. I'm so suggestible - only my HF habit is worse...

Red Flash

Fred, thanks for not posting a picture. Any threads with pictures posted give me difficulties in responding... IB needs to clean up their act and keep this site useable.

Back on topic: what does a PH test tell us though?

1.) One value is the overall PH which affects the corrosion overall. But, is corrosion only dependent on this value?
2.) And, as the additive packages decay, does the PH go up or down? In other words, a stable PH value is one indicator that all is still okay and the solution is remaining stable, maybe.

I am thinking this question is way too complex for me to answer. So, I need to really change coolant every two - three years, which given the 928 mileage I can do is sufficient.

M. Requin

I completely agree- common sense and communiity experience rule here. I a) just like gadgets so I bought one, and b) I'm fascinated by what Thomas Jefferson called "mensuration" (applied metrology to us moderns)

Hey_Allen

I'm not sure about the absolute PH value saying much, unless basing the analysis on a known starting point, as well as having more information on what it should be doing.

The strips that I have used were for a specific type of protection package, and were used to determine if a dose of the additive was required. The additive was also available by the quart, gallon, or barrel.

FredR

Having researched the issue to the extent that I can I formed the impression that an acidic environment is what needs to be avoided. It seems that there are two issues- one is exhaustion of the chemical additive package and the other is breakdown of the glycol to form acidic compounds. The bit I am not at all clear on is how these issues interact. The prime objective is to stop corrosion and as long as that is achieved how it is done is of secondary importance. Corrosion mechanisms are infamously complex and thus why it is a highly specialised field and quite often even the experts have difficulty agreeing with each other. That being said, from what I can piece together the problems start when acidic conditions exist- i.e. a pH of less than 7.

As most will be well aware corrosion is often called "oxidation" for the very reason that oxygen is quite often the main protagonist associated with corrosion in the presence of water, however it is not the only one. The coolant reservoir contains air and runs in a closed system thus a potential for corrosion but the chemical package prevents such from happening. Over time the potency of this package diminishes and sooner or later the stuff becomes a ticking time bomb. The actual pH of the coolant varies from make to make and there is a measured parameter that gives an indication of how long it takes for this inhibition process to breakdown- needless to say long life coolants exhibit longer times. The pH exhibited by coolant when fresh to some extent is a marker but what one is looking for is to establish that the pH has not dropped to acidic levels. Thus if one were to start with fresh coolant and plot pH over time one should be able to predict future behaviour for one's user profile and thus determine a finite life with a reasonable safety margin rather than throwing the baby out with the bathwater as it were. What my current test confirms to my satisfaction is that the coolant I am using is good for two years but it does not tell me it will be good for another year. There may also be other important factors in play such as how well the coolant additives protect the water pump. The coolant I use is Prestone and at the price point is well worth changing every two years. In my Cayenne I have the Porsche coolant and Porsche tell there is no scheduled need to change such - is this correct- who knows? Well at least I can check the pH to give me some peace of mind at least.

Bottom line- coolant technology has changed significantly since our 928's were manufactured. Pay more for your coolant and you should get better life expectancy. Weigh that against the cost of failure!