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I have mk4 VW Golf from 2002 and this winter the trunk's lock has gotten frozen twice and I can't open the trunk. It's not like other winters that the door gets frozen. This year is been the lock itself and I don't even can introduce the key on it when it happens.

Bear in mind that I live in Finland, so we are talking that sometimes the temps go down to -15ºC or more, and even can reach -33ºC. However, other years those temps haven't been an issue.

To fix the issue I've taken —twice— the car to the tunnel carwash, which have hot water and a drying device at the end. Last time, to try to solve the issue I filled the lock with oil and open and close it with the fog and with the keys several times after the carwash.

Yet… I figure out that the real problem is that the small door or lid that the lock has to protect it from water and debris is not working properly. It doesn't close the hole for the key completely when the key isn't there.

  • Any idea on how to solve this issue? Specially in the middle of the winter. Perhaps I should brush it with an cleaning product for grease or so. Perhaps with some lighter gas since usually is a really good cleaner of grease?
  • I read somewhere that some people carry with them "defrosters" for this occasions. What are those? I haven't heard of them.
  • Also I read somewhere that oil isn't wood for locks because, in the end it gets dirty and it make things worse. What should I use for these occasions them.

I have to add that at the beginning of the winter —on November— that door suffered a repair on the washer system. On the tubing, which was leaking, and on the pump of the rear washer which was leaking and finally broke. Perhaps the washer liquid —which is one of those for winter conditions and doesn't froze till -30ºC— fall all over the lock and is causing these problems?

Thanks beforehand!


OK after reading your comments I think I'm going to take advantage that next weekend is going to be over zero again and try to clean the lock with some lighter fluid. Brush it a little bit and try to put in place the shroud of the lock. Either by cleaning or unbending it. Then, apply some graphite dust or silicone since it seems it's better lubricants for locks.

Is this correct?

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    I've fixed the key door by un-bending the very thin metal shroud over it, which causes it to get stuck open when it's dented/bent in. Also, historically graphite powder is used as lock and key lubricant. – the_storyteller Feb 4 at 20:36
  • You might have to replace the lock cylinder. – Moab Feb 4 at 20:38
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    You say you fill with oil - but oil floats on water so water can still be there... – Solar Mike Feb 5 at 8:58
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    Use a cigarette lighter to heat the metal part of the key and use the warm key to defrost the lock. If you suspect it is leaking water in, fix it- your lock has worked for years in the cold Finland environment and only recently gives trouble. Investigate the cause and rectify it, don't set about with half solutions like filling it with oil etc; they aren't working – Caius Jard Feb 7 at 7:49
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    Where I live we have lots of freezing rain, so this is a normal part of owning a car. Not uncommon to come out to your car after work to have frozen locks in the Winter. We carry small bottles of spray alcohol designed specifically to be inserted into the lock and remove the ice (it contains a lube in it as well). I also have a small battery operated pocket heater designed for inserting into locks, but really the alcohol bottles work better... – Brian Knoblauch Feb 18 at 17:19
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Especially in winter time I've had good results with spraying PB blaster into door locks.

Do this on a dry day. If you suspect water is getting into the lock, try to spray after it's been dry for a few days. (There is no harm in spraying when it's wet but this won't be as effective.) Spraying door locks is easiest with a straw but depending on the lock a straw may not be required.

Oil repels water and a film of oil on the lock mechanism will keep water off of it, preventing it from freezing (or freezing as easily).

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After all the comments, back and forth, and for the record, I'm going to reply my own question.

The fix

What I did is the following:

  • I cleaned the key hole/cylinder with lighter fluid and a tooth brush. I've gotten quite good results in the past with lighter fluid to remove grease and other stains from places that can stand the fluid. Metals are OK. I have to brush it a lot, but finally I was able to remove most of the dirt. Inside there was a mixture of grease and mainly road —brown— debris. I even thought that there was a stone inside. I also used a small knife to scratch around inside the cylinder until the shroud in the cylinder closed the whole properly.

  • After that, I tried to remove as much fluid as I could with absorbent paper —AKA kitchen paper. When I thought it was more or less dry, I applied WD-40 on the hole, and inserted the key and move it around as much as possible and open and closed also the mechanism with the fob several times. I left if for a while.

I now that some people is not recommending WD-40 for locks, but seems that it works pretty well. Even more in this case. WD-40 stands for "water displacement" so I guess in this case is pretty much what I wanted to do. Move away the water / moisture so it doesn't freezes. What is true is WD-40 doesn't last long and you should apply other lubricant after awhile. Therefore:

  • After a couple of days, I found a small bottle of lock oil at home —which I think it has graphite— and I applied to the lock, repeating the process of introducing the key and using the fob to open the car repeatedly, so the oil spread in the whole mechanism.

Although I really think I've fixed it, at least for now, but for long, I really think that at some point I should disassemble the panel in the trunk door and check. Probably the mechanism needs a really good cleaning all around. Let's leave that for the summer.

How did this happen?

I believe that the reason that this happened was in one hand, of course, lack of maintenance.

However, besides of the lack of maintenance, the reason this probably happened is because when cleaning the snow in the back of my car the brushing pushed the some of the snow with the debris inside the lock. After a couple of years the debris keep the shroud from closing and all the rest is know history.

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