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In the owner's manual for my 2001 Ford F-150 (5.4L), in the section on "Adding engine coolant", it specifies the type of coolant to be used, and says it should be mixed 50/50 with distilled water. It explains how to open the coolant reservoir and so forth, and then there is the following paragraph (emphasis mine):

After any coolant has been added, run the engine for a few minutes to mix the coolant. Check the coolant concentration. Make sure the engine is off and cool before removing the coolant pressure relief cap (see proceeding [sic] steps on cap removal). Check the concentration per the Checking Engine Coolant section. If the concentration is not 50/50 (protection to -34 F / -36 C), drain some coolant and adjust the concentration. It may take several drains and additions to obtain a 50/50 coolant concentration.

The section on "Checking Engine Coolant" explains how to check the level of fluid in the coolant system, but in an apparent omission, does not actually say anything about how to check the concentration. I don't know how one would do that.

  • Short of a complete chemistry lab, is there actually a way to test the concentration of coolant in the system, to see whether it is 50/50 as specified?

  • Other than by somebody having added the wrong concentration, is there any reason why the concentration of coolant currently in the truck should become incorrect? Why would it be necessary to test it? (Differential evaporation rates, maybe?)

It seems like the question Is coolant testing necessary on modern vehicles? is also about some method of testing the coolant mix that's already in the vehicle. But I don't really understand what they are talking about, and it doesn't directly address my questions.

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  • Mix the coolant with the same amount of distilled water then put it inside?
    – Jean-François Savard
    Jun 19, 2015 at 1:59
  • @Jean-FrançoisSavard: Maybe I was unclear: the passage seems to be talking about testing the concentration of the coolant that is already in the car. Certainly I know how to mix coolant with water when I add it. But if the coolant system is only slightly low, I can only add a small amount of 50/50 mix, which won't do much to correct what is already inside if its proportions are wrong. Of course, if what was inside was completely wrong, one could drain it all out and start over, but again that's not what this section of the manual is talking about.
    – Nate Eldredge
    Jun 19, 2015 at 2:53
  • Oh I see what you mean. Well even if there may be other possibility I think the easiest would be to drain what is already inside and mix it.
    – Jean-François Savard
    Jun 19, 2015 at 3:02
  • @Jean-FrançoisSavard: But I don't see how I would know if that is necessary. As far as I know, a proper 50/50 mix was used the last time it was filled. I don't know why anything should have changed since then, but the manual seems to be suggesting that is possible, somehow, and I want to know why.
    – Nate Eldredge
    Jun 19, 2015 at 3:08

2 Answers 2

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In answer to the question of how to test your coolant mix, you would use an antifreeze and coolant tester

In answer to why, you would want to ensure that your coolant mixture is correct as this provides protection against icing in the winter, enhances the effectiveness of the system in the summer and provides some corrosion inhibitors to prevent your coolant system rusting or silting up inside.

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  • Thanks for information about the tester, I had not heard of this. As to the second paragraph, I fully realize that it is important to have the correct concentration of coolant inside the vehicle. What I want to know is, assuming I mixed it properly when adding it in the first place, how could it not be correct now?
    – Nate Eldredge
    Jun 19, 2015 at 14:36
  • In all likely hood the mixture will remain correct but it is worth checking. A tester is inexpensive and easy to use. The mixture could have changed due to condensation, moisture ingress, perished rubber, poorly sealing gaskets, wear in the water pump, etc... The same could be said of why bother checking tyre pressures, oil levels, brake fluid etc... I guess my response would be that only by checking it can you be sure its still correct. Time and expense of checking is nothing compared to leaving it unchecked and finding later it wasn't right when something fails.
    – Steve Matthews
    Jun 19, 2015 at 14:43
  • This is different from those other examples: obviously fluids can leak out, and that is why it is important to check the fluid level (for which you only need your eyeballs), but since the coolant and water are mixed together, they would leak out together in the same proportions, and the concentration in the system would be unchanged, you would think. So I'm trying to understand by what mechanism the concentration would change. Condensation and moisture ingress could cause that, I suppose, but the other things you mention could not.
    – Nate Eldredge
    Jun 19, 2015 at 15:00
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    The coolant element of the mixture will have different chemical characteristics to water so will boil at a different point, freeze at a different point, evaporate at a different point and pass through different sized membranes than water. I do see your point what if the level has remained the same it's a fair assumption that the mixture is roughly the same. For the sake of a couple of pounds / euros / dollars on a tester, I say why leave it to chance?
    – Steve Matthews
    Jun 19, 2015 at 15:16
  • Regular testing is not overly typical in real world applications. I have worked in several maintenance garages (Not public) and we never used testers. Levels and color are checked and if there appears to be any issue the system is checked and flushed. Your cooling system is a closed system. So any changes in color or level indicate a problem. But most often problems in your cooling system will be linked to coolant loss. Which would not affect the mixture. To change the mixture a large amount of water would have to enter, raising the level. (No other water source is available).
    – JpaytonWPD
    Dec 31, 2015 at 2:35
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Testing Coolant is pretty easy using specific gravity. A tester has several balls that have slightly different densities. Different balls will float depending on the concentration.

You want to test your concentration to be sure it wont freeze or over heat. The Antifreeze does not transfer heat very well. That is why we mix. The water does most of the cooling while the antifreeze prevents freezing. Some southern states (warmer climates) will use lighter consentrations of antifreeze. This will allow the coolant to freeze at higher temps but also cools the engine better at very high temps.

In the end, Flush the coolant if your unsure. Testing only tests the reservoir. If your coolant is clean and bright green its likely fine. If your unsure testers are available at any auto parts store.

There are Red, Yellow, and Orange antifreeze's used on some vehicles. There is usually a note on the fill cover if they use these coolants only.

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    I should add that many new cars have red coolant, so a red coolant does not necessarily mean that there is something wrong with the coolant; the car may just use a newer type of coolant.
    – juhist
    Dec 25, 2015 at 20:40
  • Good point, there are Red, Yellow, Green, and Orange. There is usually a note on the fill cover if they use these coolants.
    – JpaytonWPD
    Dec 27, 2015 at 22:05
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    Isn't it called specific gravity?
    – Ppoggio
    Dec 28, 2015 at 2:28
  • You are correct. Thanks. Thats what happens when I type faster than I am thinking.
    – JpaytonWPD
    Dec 28, 2015 at 13:26

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