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HC and CO2 in Coolant

  1. Aug 22, 2015 #1

    I want some information regarding HC and CO2 in Coolant (Car cooling system).

    As you know when the sealing (head gasket) between water jacket and combustion chamber fails, the engine smoke will enter cooling system which contains HC and CO2.

    I know that CO2 makes coolant acidic and reduces it's PH value.

    Engineers use this method to determine head gasket failures.

    My questions:

    Will CO2 makes coolant permanently acidic? or just temporarily?
    Will CO2 remains dissolved in coolant after some hours later when you switch off the engine?
    How much reduction of PH occurs when CO2 enters Coolant?

    If engine cools down and i drain a sample of coolant, is it still possible to see PH changes or maybe cold coolant makes the test invalid?

    What i want to do is that i poor new coolant into the car and measure it's PH.
    Then i drive the car for about 2 days and measure it's PH again.

    If the PH value reduces, does it mean that there is a head gasket leak?

    Thanks for your scientific explanations.
    Last edited: Aug 22, 2015
  2. jcsd
  3. Aug 22, 2015 #2


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    Staff: Mentor

    Smoke contains HC and CO2, or cooling system contains HC and CO2?

    Answers depend on the composition of the coolant, but I am afraid they can be handwavy at best. pH change is most likely temporary, but can last for hours or even days - so a lot depends on your definition of "temporary".
  4. Aug 22, 2015 #3
    Yes, you're right i wanted to say SMOKE contains HC and CO2.

    My edited sentence:

    the engine smoke which contains HC and CO2 will enter cooling system.

    So, you believe that at least PH change will remain for hours.

    My definition of temporary is 24 hours.
  5. Aug 23, 2015 #4


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    Staff: Mentor

    As I wrote - this is all quite handwavy, but the general idea is - as long as there is CO2 present in the coolant, its pH is lowered (assuming coolant contains at least some water, please remember pH refers to water solutions, acidity of non-water solutions, while they may contain H+, is technically not described by pH). pH will get back up with CO2 leaving the system. As long as we talk about a closed system, into which CO2 was injected under pressure and has no chance to leave, pH change can be quite stable.
  6. Aug 23, 2015 #5
    I talk about a combination of coolant and distilled water (or water).

    As i said above, i want to pour new coolant into a car with suspected head gasket leak. The new coolant which is prediluted (distilled water and antifreeze 50/50) has a PH value of 8.5.

    Then i drive the car for about 2 days and after that i measure the coolant PH and compare it with when it was new.

    If in a very short period of time (2 days), the PH decreases it means that there is a leak in the system most probably head gasket leak because the car already has coolant loss problem without any outside leak.

    So. if PH change remains stable in this period of time during which i perform my test, then i can rely on PH test.

    What i am afraid of is when i let the car to cool down to be able to open the radiator cap. I was afraid of this moment of opening the cap to let CO2 gases out the system and increase PH value again.

    Is opening the cap result in CO2 escaping from the system and increasing PH back to normal value?
    Last edited: Aug 23, 2015
  7. Aug 23, 2015 #6


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    Staff: Mentor

    Yes, but it is still a process that takes hours. No idea how you measure the pH (actually fact that the solution is 50% antifreeze can already pose a problem and make the measurement unreliable), but if you do it fast the result should be indicative.

    Note that if you take a sample of the coolant to measure the pH, sample - most likely having a much higher surface area/volume ratio than the coolant closed in the cooling system - will loose CO2 much faster. Still, few minutes shouldn't be a problem.
  8. Aug 23, 2015 #7
    So, if antifreeze pose a problem i can fill the system with only water to eliminate this issue.

    Doing it fast means i should measure the sample's PH while it is still hot. Is measuring a hot fluid with PH meter harmful for the device?

    I did a test yesterday to see how much time it takes for CO2 to escape from water.

    I poured some water into a glass and measured it's PH. It was 7.5

    Then I blew into the water for about 3 minutes and re-measured it's PH and it decreased to 6.8

    I left the water in the glass for about an hour and measured it's PH again and it increased just by 0.1 to reach 6.9

    If my 3 minute exhaling reduces PH by 0.7, i think head gasket leak should lower PH much more severe.
  9. Aug 23, 2015 #8


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    Staff: Mentor

    Depends on the electrode. Some are designed to work in hot fluids, some are not. You will definitely need to calibrate the electrode/device for high temperatures.

    Note if you take a sample and keep it closed (in a small vial, bottle, or just a syringe) till it gets cold, and there is not much head space above the liquid, carbon dioxide will mostly stay in the solution.

    Sounds reasonable.

    Definitely, amount of CO2 injected under pressure should be much higher.
  10. Aug 23, 2015 #9


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    Acidity in coolant from exhaust gas leakage is due partly to NOx . Sometimes SOx as well depending on fuel .
  11. Aug 23, 2015 #10
    I can also let the coolant to cool down in the cooling system and then open the cap and measure it's PH immediately! What about this?

    I have read in most sites that HC and CO are the main factors contributing to make coolant acidic but here i just wanted to talk about measuring coolant PH not the gases.
  12. Aug 23, 2015 #11


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    Staff: Mentor

    Slower, as it is easier to cool down small volume of the coolant, than to wait for the whole engine to cool down. But it should work as well.

    No such thing as gas pH, as I explained earlier - pH is a property of water solution.
  13. Aug 23, 2015 #12
    Yes, your idea seems more reasonable.

    I wanted to say that this topic is only related to coolant PH and has nothing to do with the type of gases which may enter cooling system.
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