Why the lock freezes, and why it is usually not the lock
Two different things get called a frozen door, and they want different products.
A frozen cylinder is water that got into the key barrel and froze around the wafers. The key goes in part way, or goes in and will not turn. This is the one a lock de-icer is for.
A frozen door seal is the rubber weatherstrip around the door frozen to the body. The key turns, the handle works, the door does not move. No amount of de-icer in the keyhole helps, because the keyhole was never the problem. This is by far the more common of the two on a modern car, and it is the one prevention actually solves.
Work out which you have before you spend anything. If the key turns and the door will not open, put the de-icer away.
How we judged these
Can you carry it? This is the first criterion and it outranks the chemistry, because a lock de-icer in the glovebox of a locked car is a product that has failed at the only moment it was needed. The ranking below is heavily shaped by size: the half-ounce tube that fits a keyring beats the bigger bottle that does not.
Does it lubricate as well as de-ice? The good ones do both. Melting the ice and leaving the cylinder wet sets you up to repeat the exercise tomorrow; leaving a lubricant film behind displaces water and is why a treated lock tends to stop misbehaving.
Does the maker publish a low-temperature figure? Almost none do, including both de-icers here, and we record that as unpublished on each entry. The exception is the silicone spray ranked third, which publishes a range of -100 F to 500 F and is stated safe on rubber and vinyl — which is exactly what a door seal is made of.
The cheapest preventable problem on this site
A lock de-icer is a few dollars. A locksmith call-out, or a tow to one, is not — and neither is the morning you lose. This is one of very few items on this site where the preventative product costs less than a cup of coffee.
But the honest version of the arithmetic is this: the cheapest fix is not a product at all. It is one minute in October with a can you probably already own, wiping silicone along the door seals so they cannot bond to the body. That costs nothing extra if you are already treating the garage door seal with the same can, which is the job it was bought for.
We would rather tell you that than sell you three products. Buy the keyring tube because it is trivially cheap insurance, then do the prevention so you never reach for it.
Skip this
Skip the hot water, and definitely skip the lighter
Hot water is the internet’s favorite answer and it is a bad one twice over. Poured on glass it risks thermal cracking. Poured on a lock or a seal it runs into the mechanism, the door skin and the weatherstrip, and then refreezes into considerably more ice than you started with — usually somewhere you cannot reach.
Heating the key with a lighter and pushing it in is the other classic. It can work on an old all-metal key. On a modern key it is a genuinely expensive idea: the plastic head contains a transponder chip and a battery, and replacing a coded key is a dealer-priced part plus programming.
Also skip forcing the door when the seal is frozen. Pulling hard enough to break the ice bond can tear the weatherstrip off the door, and a torn seal leaks water and wind for the rest of the car’s life.
The method, in order
1. Try another door. Obvious, free, and it works surprisingly often — the passenger door is on the side that took less weather, and the rear doors are used less and are often drier.
2. If the cylinder is frozen, apply de-icer into the keyhole and give it a minute. Do not force the key while the ice is still solid: keys shear, and a snapped key in a frozen cylinder is a much worse day.
3. If the seal is frozen, break the bond along the edge. Press the door firmly inward around its perimeter with the flat of your hand to crack the ice, then pull. Steady pressure rather than a yank.
4. Warm the key, not with a flame. In your hand, in a pocket, in a cup of warm water and dried. A warm key introduced slowly does what heat is supposed to do without the transponder problem.
5. Once you are in, dry it and treat it. The lock froze because water was in it. De-icer displaces water; a shot of silicone or a proper lock lubricant afterwards is what stops it recurring next week.
Prevention, which takes about a minute
Do this on a dry day in autumn and you can forget the rest of this page.
Silicone on the door seals. Spray onto a cloth, not directly, and wipe the rubber weatherstrip around every door. It stops the rubber bonding to the paint when wet, which is the single biggest cause of a door that will not open. The WD-40 Specialist silicone ranked third here publishes a range from -100 F and is stated safe on rubber and vinyl.
Something in the cylinder. A shot of a lock lubricant or de-icer displaces whatever water is sitting in there before it has a chance to freeze.
Cover the keyholes if the car is stored. A strip of tape over the barrel on a car that is not being driven keeps the water out entirely — worth doing if you are putting a car away for the season.
One last honest note: many drivers now unlock by fob and have not put a key in the barrel for years, which is exactly how a cylinder gets seized and full of water without anyone noticing. If your car has a physical key you never use, that is the lock most likely to fail you on the morning the fob battery dies.
