To keep things short I poured 200ml of concentrated genuine ford super plus premium antifreeze (Ethylene glycol based) within a bowl. Then added 200ml of water to dilute the solution to a 50/50 mixture. It states on the bottle when mixed 50/50 with water the antifreeze should protect to -37 degree's Celsius however when tested with a floating balls tester it shows that the solution would only protect up to -23 degrees. To investigate further I purchased two more hydrometer (different manufacturers) which tested the solution at -23 same as the first hydrometer. I don’t believe that three hydrometer from different manufacturers are going to lie to me so I’m puzzled.

After some research I found that -37 is the protection level that a 50/50 mixture should provide this is why I am confused.

My question is what should I do? Should I add more antifreeze increasing the strength to -37 or should I keep the solution at -23 when using within my car? If there is anyone that can give information to why this may be I would be more than grateful.

Thank you all for your time

3 Answers 3


The difference you observe is quite notable, so I wondered how reliable it is to just measure the density (which is what your hydrometer does).

From the datasheet of your Ford antifreeze, the density is 1.10kg/l, while pure ethylen glycol has 1.10kg/l. Glysantin is another brand for antifreeze and states 1.122-1.125kg/l for its G48 (sorry, german)

This differences aren't big, are they?

Water has a density of 0.998203 kg/l (at 20°C, as all values above), so one could approximate the density of any mixture by a linear function:

enter image description here

From this, a 50% mixture from Ford Super Plus Premium has a density of 1.047kg/l. The same density has a 40.7% Glysantin G48 and a 45.4% Ethylan Glycol mixture.

According to Glysantin's website, a 1:1.5 mixture (i.e. 40% antifreeze) protects down to -27°C instead of -37°C, which is a vast difference!

For pure ethylen glycol, I found this chart (in °F):

enter image description here

which also shows a serve reduction for lower concentrations of antifreeze.

So, slight differences in density of the andifreeze will result in very different temperatures displayed on a hydrometer.

This still does not explain your reading of -23°C, but the linear function is just an approximation, temperature changes density, too, and who knows what other effects there are.

I think you can thrust a 50% mixture, but can increase it to 60%, as Paulser2 already said. However, pure water has the best cooling capability, and the more antifreeze you add, the worse it gets. Too much antifreeze, and you may get a heat problem in the summer.


The first thing to look at is, did you actually mix like amounts to come to a true 50/50 solution? As with any scientific study, you need to make sure your results are repeatable. You bought two other antifreeze testers (hydrometers) to ensure your measuring device was good, but what you didn't do is try to make the mixture again (at least you didn't say you did).

Another thing you could also do is try a different type of antifreeze tester. There is a thing called a refractometer which uses light through a prism to identify how the solution works out. This is far more accurate than the bouncing balls, though is surly more expensive. This will give you a far more accurate reading.

NOTE: The above was just things you need to think about in your testing to ensure accuracy of your tests.

To answer your main question, yes, add a bit more antifreeze to bring it up to snuff, especially if you live in an environment which requires the extra protection. In severe climates, a mixture of 70/30 antifreeze to water is quite normal, so there should be no issue going to this level of antifreeze in your system.


Many testers are of such low quality that they can't be trusted. Also, temperature plays a part, and the solution should be at 60 deg. F. to have accurate results. If you are using the non-toxic Propylene glycol type, a tester for the regular ethylene glycol can't be used. A refractometer is the only really accurate way to test it, but the good ones are close to $100 and the cheap $15 ones may not be very accurate. Don't trust the floating balls testers, there is a reason they only cost $2. The ones that have a pivoting pointer are much more accurate.

  • Many years ago ( I guess they still do it ) , manufacturers added 5% water to ethylene glycol to lower the freezing temperature. The problem was , with antifreeze stacked outside in the winter , with the temperature close to 30 F , the 100 % antifreeze would nor pour out of the can. It is hard to explain to a customer who wants to top up his antifreeze that the new antifreeze is frozen. So a little water was added to reduce the freezing point. Jan 11, 2019 at 17:35

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