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How can I tell whether antifreeze has been mixed already?

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bwringer

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I have a jug of Prestone antifreeze. It's the kind you mix with distilled water to make a 50/50 mix. Nothing exotic.

It seems like it's been opened, but it's been a few months since I bought the stuff and I can't remember for sure whether I already mixed it or not. I usually mark the jugs clearly with permanent marker, but I might have wandered off in search of a marker and somehow never returned... or I might not have. Dunno.

Anyway, all the float style antifreeze testers I can find will tell you whether your AF is mixed with too much water (Why? Is sneaky extra water a thing that happens a lot?), but they won't tell you the difference between plain and mixed.

Is there a foolproof tool or technique for this?

Surely I'm not the only one with the memory of a squirrel... :eyecrazy:
 
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bczygan

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Use a tester:

antifreeze_tester.jpg
 
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bwringer

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Reading R Hard

The testers are the problem -- the commonly available testers with floats or balls will give nearly identical results with a 50/50 mix or with straight antifreeze.

They will allow you to tell if there's excess water in the mix, but they won't tell you for sure whether there's no water in the mix.

Perhaps I could take a sample of my mystery fluid and mix it 50/50 with water. If I get the same results, it was 100% AF.

If I get different results, then it was already mixed (started as 50/50, now 75/25).
 
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bob15

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Take a sample and look at it. If it is 50-50, it will be diluted looking. Pure antifreeze will look like Mountain Dew.....pure green and much thicker in consistency.

Not to sound like a smart-***, but have you ever seen pure anti-freeze out of a container? Does it look like that when you take a sample?
 
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brass89

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if using a coolant tester (decent one) it should definitely show differently from a full concentrate to a 50/50 mix. if the mix is concentrate, designed to be cut 50/50 to bring it to usable antifreeze - it will show within normal ranges. if it's still in concentrate form it'll be off the charts. if it reads protection around -28 to -34, it's mixed. if it reads something ridiculous, it's concentrate. if you're using a tester that can't tell the difference or shows no difference between the two, throw it out and get a real one.

refractometers are more accurate but a little more technical in use (from a standard easy read tester).

also depends what kind of coolant, ethylene glycol or propylene glycol. i'm guessing the prestone all in one or whatever is eg. in addition, you can tell from the 'feel' if you're familiar with antifreeze. full concentrate tends to be dark although i can't remember if the prestone is green or clear/yellowy tint. by feel concentrate will be thicker and more oily than diluted. honestly, best way is with a tester to be sure. good luck.
 
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bcradio

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If you are looking at this from a return on investment standpoint, then get another jug of undiluted antifreeze to compare it to. Then you'll have the new jug for when needed and know the status of the old jug.

If you are looking for a new tool, then get the tester.

This assumes you only have a 50/50 mix or pure antifreeze with no other ratios possible.
 
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gte718p

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I vote for dispose of properly and spend $6 to buy a new can of antifreeze.
 
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wild cowboy

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brass89 said:
if it's still in concentrate form it'll be off the charts. if it reads protection around -28 to -34, it's mixed. if it reads something ridiculous, it's concentrate.
Click to expand...
surprisingly, when referring to typical antifreeze (ethylene glycol based) full 100% antifreeze does not provide anywhere near the protection of 50/50

chemistry can be weird like that!

freeze_points.gif
 
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BCJohnstone

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You're on the right track. Although a refractometer is the proper tool to test coolant, they are also kind of pricey.

Just use your squeeze bulb tester. Fill a cup with some coolant and cut it with water. If the reading changes (freeze point raises) it will tell you what you had to start with.

Be careful with those squeeze bulb testers though. Straight coolant will max out the gauge because the freeze point is greater than the -45 (possibly -80 or so) Once cut 50/50 the freeze point will be around -40, -45 (still maxing out the gauge). So just be careful. -35 to -40 is more than adequate for a vehicle around here (Massachusetts). Unless you live somewhere like Alaska, you should be good with that.
 
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454cid

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BCJohnstone said:
Be careful with those squeeze bulb testers though. Straight coolant will max out the gauge because the freeze point is greater than the -45 (possibly -80 or so) Once cut 50/50 the freeze point will be around -40, -45 (still maxing out the gauge).
Click to expand...

That is incorrect. Straight coolant will freeze before a solution of coolant and water.

freeze_points.gif


The blue line is what you want to look at. Not many people are using propylene glycol (the red line).
 
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