Jc Maxwell wrote:
> Since the keyless entry system stopped working last year, I've had to
> use the old-fashioned keyed locks, and number pad, to access my 1998
> Mercury Grand Marquis.
>
> Driver door and trunk locks work flawlessly, but the passenger door
> lock is uncooperative. It seems as if it only works when the
> temperature is somewhat warm - let's say, above 50°F. Which it is
> here only sometimes in the afternoon, this being winter in my area.
>
> It goes like this: I'll insert the key, attempt to turn it...but, it
> doesn't. Maybe wiggles a little. That's it. I'm not going to force
> it, since I don't want to break the key off in the lock, and it
> probably still wouldn't turn.
>
> At least part of the locking mechanism does function. I can unlock
> and lock the passenger door from either the driver's side number pad,
> or door-mounted lock/unlock switches (both driver and passenger
> side). It's only directly turning the lock with the key which
> doesn't work.
>
> I've tried rattling the key in the lock. No good.
>
> I've tried my extra key. No difference.
>
> I've squirted some graphite lube in the keyhole. That helped when
> the lock stopped wanting to turn a couple of years ago. This time,
> it didn't help.
>
> I'm reluctant to put anything else in the keyhole. Someone suggested
> WD-40, but that seems like a terrible idea, since it's not actually a
> lubricant. 3-in-1 or other oil could gunk up something sensitive.
>
> Ours is a very dry climate, so I doubt anything is binding up due to
> rust anyway.
>
> Short of taking this to a mechanic, any ideas?
>
> How much of a project would it be to swap out the lock myself? Am I
> going to run into headaches due to the vehicle's notorious
> first-generation PATS?
>
> It's weird that the *passenger* door lock has seemingly worn out,
> since it's the driver side lock that gets used most often.

Two possibilities,

Dirt/dust in the lock is mixed with the lube and causing it to gel and
bind when it's colder.

Because the lock wasn't used for a long time it has a small amount of
corrosion in between the cylinder and the plug (rotating part the key turns)

Either way -
Go get a can of brake cleaner, make sure it has the straw.
A can of compressed air - with a straw (or if you have a compressor a
small tipped blow gun)
and some graphite based lock lube.
Now use a bit of tape and tin foil to mask around and under the lock
(mainly to keep you from spraying the cleaner around and to protect the
paint during the next step).

Hold open the key door, stick the straw in as far as it will go.
Give it one short blast of cleaner.
Now insert your key and try to turn it. It probably won't turn very well
if at all.
Repeat the cleaner and key until the lock frees up. The cleaner will
spray through the tumblers and wash out the crud around the plug,
turning the key acts like a scraper and will break loose the crud so the
spray can work.

Now once you get it freed up. Hold the key door open and use the air to
blow through the lock and dry it.
Apply the lock lube into the plug and apply a quick shot of air to push
the lube out around the plug. Apply some more lube and repeat until the
lock works the way you want it to.

Don't use any type of liquid lube in the lock, it just gums them up and
causes problems.

--
Steve W.