Frozen Car Door Locks

Use a lock de-icer with a fine nozzle, applied into the keyway, and give it thirty seconds. If you have none, warm the key itself and insert it slowly - never force a key in a frozen lock, because a snapped key in a cylinder turns a five-minute problem into a locksmith.

Why a lock freezes when the rest of the car does not

A lock cylinder is a small metal cavity with narrow gaps around spring-loaded pins. Water gets in through the keyway - rain, a car wash, condensation - and there is nowhere for it to drain. When it freezes it locks the pins in place, and the mechanism physically cannot move.

It takes very little water. That is why a lock can be frozen solid on a morning when the doors open fine and the windshield only has light frost.

What to do this morning

1. Try the other doors first. Locks freeze individually, and the passenger door is often fine. This costs ten seconds and solves it more often than people expect.
2. If you have lock de-icer, apply it into the keyway and wait thirty seconds. It is alcohol-based and it works fast in a small cavity.
3. If you have no de-icer, warm the key. Hold it in a gloved hand, use a lighter carefully on the metal blade only, or hold it against a hand warmer. A warm key conducts heat into the pins.
4. Insert the key SLOWLY and do not force it. Let the warmth do the work, withdraw it, warm it again, repeat. This takes a few cycles and it is the safe method.
5. Press on the lock area with a gloved hand first. Body heat through a glove is slow but it is free and it does work on light freezing.

The WD-40 question

People search specifically for this, so it deserves a straight answer: WD-40 will usually free a frozen lock, because it displaces water. That is literally what the WD stands for.

The problem is what it leaves behind. It is a light penetrating fluid rather than a lock lubricant, and it washes out the graphite or PTFE lubricant a lock cylinder relies on. Use it once in an emergency and re-lubricate the lock properly afterwards. Use it every week all winter and you will end up with a sticky, gummed-up cylinder that jams for reasons unrelated to ice.

A dedicated lock de-icer is a couple of dollars, evaporates cleanly, and does not have this problem.

The rule that makes any of this work

Lock de-icer inside the locked car is the most predictable failure in winter motoring. It has to live somewhere you can reach without opening the car:

• A coat pocket, from November.
• A bag you carry.
• By the front door at home, so it is with your keys.
• A second one at work, if you park outside there.

Keyless entry does not exempt you

Almost every car with a proximity fob has a hidden mechanical keyhole, usually under a plastic cap on the driver's door handle, and a physical key blade hidden inside the fob itself. Both exist for the day the fob battery dies - and both freeze exactly like any other lock.

Find yours now, while it is dry and light and you have the manual to hand. Standing in the dark in January trying to work out how a door handle cap comes off is not the moment to learn.

Stopping it happening at all

1. Apply a graphite or PTFE lock lubricant to each cylinder in the fall. It coats the internals so water cannot sit on them.
2. Cover the keyhole with a small piece of tape before a freezing rain event if the car is parked outside for it. Crude and effective.
3. Treat the door seals with silicone at the same time, since a frozen lock and a frozen door tend to happen on the same morning. See how to prevent frost overnight.
4. After a car wash in freezing weather, work each lock a few times with the key so the mechanism is not sitting full of water when the temperature drops.

If the doors themselves are frozen shut rather than the lock, that is a different technique - and forcing that one tears the weatherstrip off the door.