At low is antifreeze really rated?

I live in Montana and we’ve been experiencing severely unpleasant lows in the -20s and -30s (Fahrenheit). These are real temperatures, not wind chill temperatures…unfortunately.

While driving on the highway, I began to wonder exactly how cold it could get before I need to worry about the antifreeze freezing – and the block in my Ford F-150 pickup truck potentially cracking.

If your standard 50/50 antifreeze-water mix is rated to -34F, does that mean the antifreeze stays liquid until the temperature reaches -34F or does the antifreeze start getting “slushy” at -30F and will be frozen solid at -35F?

I know that windchill is a number made up for humans and should not apply to machinery, but when driving 75mph with the radiator at the front, it’s hard to think that windchill may not play a factor?

Obviously, I could alter the antifreeze/water mix to give me greater freeze protection, but I don’t hear a lot of folks doing that.

You have the perfect lab at your disposal to figure this out yourself and then you won’t have to base your conclusions on someone’s elses opinion.

What I suggest is to blend several mixes of anti-freeze/water and set them out overnight and periodicaly check what is happening to these test blends.

Doing things for yourself has so many advantages to getting some type of answer off the net. Besides what else is there to do in Montans in the winter :slight_smile:

Good suggestion. I’ll set my various antifreeze mixes outside…as soon as I can get the frozen back door open! :slight_smile:

A dilemma is that a virtual heatwave of +20F is predicted for this weekend, so my experiment will have to wait.

Thankfully, Montana only gets a few of these -30F weeks per winter. The problem is that issues like this can be somewhat skirted by the lazy soul. (I’m reluctant to leave the house when it’s -35F, let alone make a road trip.)

I should probably just alter the mix to be on the safe side, but was curious if there was a general consensus on antifreeze ratings. Who knows. Maybe I shouldn’t focus on antifreeze ratings, but more on moving south! :slight_smile:

The back of the bottle contains a mixing chart that tells you what proportions to mix to be safe at what temperatures. Yes, below that it begins to get slushy. And eventually, solid. Materials go through a transition phase from liquid to solid.

You may recall that water expands when it freezes…therein lies the problem. But beyond antifreeze, you have another protection. Your engine block has “freeze plugs”. These are like metal “caps” pressed into what are actually casting holes, and these plugs will be forced out of the coolant freezes, usually preventing cracking of the block.

“Chill factor” is actually just a representation of how quickly heat is dissipated. Water at -20 ambient with a -40 chill factor due to wind will be drawn down to ambient as quickly as water would in -20 without any wind. The temperature of the water will never be drawn below ambient.

In the case of your engine going down the highway, the air going through your radiator does remove heat much faster than if the car was sittting at a stop. But remember that the engine is constantly generating heat, a substantial amount at 70 mph, and the thermostat is regulating the flow of the coolant to enable the engine to keep at running temp.


  • Chill factor applies to machinery as well as humans. But it only represents how quickly heat is dissipated, not how low it’ll go. It’ll never go below ambient.

  • the temperature to which you’re protected based on your “mix” is on the back of the bottle.

  • you have additional protection against freezing damage beyond your antifreeze.

  • your engine is generating plenty of heat to replace the heat dissipated for all but the most extreme conditions. And the faster you’r going, which is where the chill factor becomes more pronounced, the more heat it generates, offsetting the chill factor effect.

Since you’re temps are getting so low, let me recommend having a block heater or lower radiator hose heater installed and plugging the car in overnight as added protection. We all did that when I lived in North Dakota. We also blocked part (or all) of the radiator with corrogated cardboard or a small piece of blanket to try to keep the heat in. That also helps in getting the car warmed up some in teh morning.

Montana too here. My old home in North Dakota is probably best lab in lower 48.
Anyway, I don’t know anyone that does not use 50/50 and © I don’t remember a freeze-up car problem in 54 years driving. You can get past the 75mph in 30 below
by checking out how much heat your engine is producing and what it takes to freeze
50/50 to the point of turning into a solid plug or cracking metal.

Thanks same mountainbike. This answers my question about windchill – one of the more hotly detbated aspects of the antifreeze conversation in the house last night! :slight_smile:

I do have plug-in engine block heaters on both my vehicles – and highly recommend them too for cold morning starts.

Maybe this is getting a hair off topic, but you mentioned blocking part or all of the radiator with corrugated cardboard. I’m assuming you just did this when warming the car up and not while driving? I ask because I’ve seen cars driving down the highway with pieces of cardboard strapped to the grill in the wintertime.

Any off the shelf premixed antifreeze sold in Montana should be good for -40F. That’s close to a 50/50 mixture. Antifreeze does not solidify like water and burst you rad or engine block. It turn thicker and will still pump. If you’re really concerned go 55/45.

Nope, we did it while driving. Wind passing through the radiator disspates heat far faster than if idling. Without the blockage, the car would take way too long to heat up. This is hard on the engine and harder on my delicate derriere.

Typically, we’d hang it in a manner that we could adjust the amount of blockage, much as the “venetian blind” grills on the Peterbuilts do.

Close and close enough for the case in point.

Windchill only accurately measures the effect on skin. Skin is warm and moist. So humidity does come into play (note: I have seen some formulas that did not appear to adjust for humidity.)

For a car, wind is a factor increasing the cooling or warming of a car. There is no way wind can cool a dry below the standard temperature. dry on the outside) further than the simple temperature. It just dues it faster.

Not all coolants are equal so check the numbers on the coolant you have in your car or that you plan to put in your car.  If it is over say 3 years it would be a good time to change it.  Read the label. Mix accordingly [b] Note: when you read the label you will likely see that using too strong a mix can cause the mix to freeze at a higher temperature. [/b]

Wind chill does not apply to inanimate objects. They are always at ambient temp no matter how fast the wind blows. Objects that are warmer than ambient are affected by wind chill only to the extent that more heat is required to keep the temperature the same. Running engines provide the temp to keep the coolant warm. When not running ambient not wind chill applies.

Wind chill formulas are generally published for the dissipation of heat from human skin, it’s true, but the published formulas simply assume a coefficient for an assumed moisture content in the skin. Water transmits heat far faster than air. The moisture in the skin transmits the heat far faster than of the skin were truely dry.

But the concept is the same for all matter. All matter will only chill to its surrounding temperature, including human skin. Wind affects how fast that happens. The rate at which the heat transfers varies depending on the properties of the matter itself and of the properties of its surrounding matter, the matter to which the heat energy is moving.

I would argue that a radiator, being copper and designed to dissipate heat, would also cool coolant far faster with wind than without. Perhaps even as fast as a human body part. Perhaps faster.

But I also concede that the curve for heat dissipation on human skin might be different than the curve for a radiator. I concede that the published “wind chill” numbers would probebly be a bit different.

I’d also argue that my definition was probably a better approach to understanding the problem than saying wind chill only applies to skin. Perhaps I could work on that.

Here’s how I look at it. If it gets so damn cold that the antifreeze freezes, nobody’s goin’ anywhere!


No. Wrong. Wind chill is all and only about perceived temperatures. If only someone here had a computer so they could verify common knowledge like this by looking up stuff like this on the internet.

““Chill factor” is actually just a representation of how quickly heat is dissipated. Water at -20 ambient with a -40 chill factor due to wind will be drawn down to ambient as quickly as water would in -20 without any wind. The temperature of the water will never be drawn below ambient.”

Would you like to revise and extend your remarks? Because that just makes no sense at all.

“In the case of your engine going down the highway, the air going through your radiator does remove heat much faster than if the car was sittting at a stop. But remember that the engine is constantly generating heat, a substantial amount at 70 mph, and the thermostat is regulating the flow of the coolant to enable the engine to keep at running temp.”

The thermostat does not keep the engine at running temp, it tries to prevent the engine from running at a temp so low as to be inefficient and to reduce emissions.

You might also want to adopt my morning ritual of checking the bypass hole.

Speaking from experience (fortunately not mine), the block cracking is sort of like the pipes freezing. Ice starts to form at one temperature, but it has to get somewhat colder before it can overcome the confining pressure of the cooling system and freeze completely, thus cracking it open.

I knew a lady who ran straight water in her older Crown Vic for a few months in the winter with no apparent ill-effects. Her car was squealing when she first started it but would eventually go away. I offered to look at it for her and I found the water pump was seized up. When I took it off, some very rusty ice poured out.

I guess what had happened was that a radiator hose had burst a few months earlier and some relation of hers replaced it and just topped it off with a hose. So the water froze overnight, but somehow didn’t break anything (I wonder if it’s because her radiator cap was shot too?) and when she started it up the belt would skid over the water pump until it warmed up and it thawed. I drained the water and put in some antifreeze and it was good to go!

Also, re: the wind chill. Wind chill will only reduce something’s temperature to the ambient temperature so if it’s, say -30 out, wind will get something’s temperature down to -30 a lot faster, but it can’t make it any colder than -30.

Also, also, you are aware of the existence of hydrometers, right? They’re like little eye-dropper things with different balls that float at different antifreeze/water concentrations and will tell you the approximate freeze and boil-over temps of your coolant.

Wind chill can’t make the temperature any colder. I have had temperatures go to -40 and have not had my coolant freeze. 50% is about what I used, sometimes better.

“Prestone antifreeze, at 50/50, provides protection down to -34F degrees.” "Prestone antifreeze, at max 70/30, provides protection down to -84F degrees."
Wind COOLING applies to things other than exposed flesh. Wind CHILL applies to APPARENT temperature on exposed flesh, equivalent to a certain temperature.

As others pointed out…Windchill does NOT effect how cold something will get…only the rate at which something cools. If the outside temp is 40 degrees and the windchill is 20…a glass of water will NEVER freeze.

50/50 is a good mixture unless you live in Alaska or Northern Canada. When its colder then -34 I’m staying at home around a nice fire. I’ve only seen below -30 a couple of times…and I don’t want to again. If you live in temps where it gets below -34 you have other things to consider…like getting a block heater.

Caller X, you too have a computer.

I always provide an explanation for my arguements, and am always open to dissenting opinions and to added information. If you’re saying it’s "simply wrong, then you have an obligation to provide at least an argument for your statement. You have a computer, you’ve made the statement, you do the research.

Caller X, do you have some sort of personal problem are are you just incapable of understanding anything technical? You’ve repeatedly and unsolicitedly insulted me in a number of posts now without offering any contradicting arguments, facts, data, or anything else. I’ve come to realize that your knowledge base is extremely limited. But I cannot figure out why you’re taken to repeatedly insulting me.

And what, exactly, did you think “running temp” meant?

What is going on with you?