Bicycle Mechanics - stiffened headset?

So my old Raleigh fixed conversion has suddenly gone and got stiff steering. I removed and reinserted the stem in order to make sure that the stem hadn't just got kind of stuck itself, and that didn't do anything. Anyone want to offer an educated guess or a reasonable list of tests to go through to determine the problem. Can this happen from the onset of freezing temperatures? The stem itself is well-greased and fits fine. It's the original stem, so there isn't an issue of size compatibility. Do headsets just go and get tight one day, or did this just happen so slowly I didn't notice it?

The headset shouldn't all of a sudden 'tighten up' by itself. I'm not too sure, its happend to my bike before, i took the stem off, and put it back on, then tightent the headset up, and it felt really stuck and stiff, although i rode it for a bit and it seemed to lossen up again. Could this be because you might have tightened the headset bolt up to tight?

I haven't touched the headset. Nor had I touched the stem until it stiffened up. Can this occur do to cold weather? Temperatures dropped here last week, just about the time I started riding a lot again. The stem's alloy, frame's steel.

Is this a sign that I need to overhaul the headset bearings? Maybe the grease has got too old?

Is this a sign that I need to overhaul the headset bearings? Maybe the grease has got too old?

It's more than a "sign". It's an unmistakable warning. How long has it been since the headset was overhauled? You may have water and/or dirt in there, you may have a broken bearing or a cracked race. Find out soon!

I saw that same exact symptom here in Minnesota a coulpe weeks ago when we were getting ready to ride. The guy had his bike inside his vehicle when he got to the trail head. He took it out and got ready. About ten to fofteem minutes later he grabbed his bike and noticed that he had to "brake" his headset loose. It remained stiff after that.
He gave it to me to bring to the shop because his replacement front triangle had come in from warranty and he was having it swapped. I noticed when I took his fork out that a lot of water drained from the headtube area. I overhauled the Chris King headset and there wasn't mauch of anything in it. I think that the steering got stuck/stiff from the water freezing between the steerer tube and the headset cup more so thatn from water in the headset freezing.

I saw that same exact symptom here in Minnesota a coulpe weeks ago when we were getting ready to ride. The guy had his bike inside his vehicle when he got to the trail head. He took it out and got ready. About ten to fofteem minutes later he grabbed his bike and noticed that he had to "brake" his headset loose. It remained stiff after that.
He gave it to me to bring to the shop because his replacement front triangle had come in from warranty and he was having it swapped. I noticed when I took his fork out that a lot of water drained from the headtube area. I overhauled the Chris King headset and there wasn't mauch of anything in it. I think that the steering got stuck/stiff from the water freezing between the steerer tube and the headset cup more so thatn from water in the headset freezing.

Sounds logical to me. If you store your bike in any heated space, the warm moist air will infiltrate anyplace that isn't air tight. Take it back out into the cold and the water in that air will condense and freeze.

Could just be that your grease is too high a viscosity at the new colder temps, too... Does it turn freely after warming up indoors for a few hours?

Just checked the steering. After a night of sitting in my warm apartment, it's definitely looser, but it still feels kind of tight. There's no sound or grittiness, and no play, but it doesn't flop around like I'm used to on some of my other bikes. I think I'm going to take apart the headset and take a peek inside. Interesting points about the warm, humid indoor air infiltrating. Hadn't thought of that before, but I guess that's why there's such a thing as sealed bearings and headsets, right? Is there such a thing as sealed headsets? I'm so used to working on these older bikes that I don't really have a lot of knowledge about the newer stuff.

Thanks for the proffered suggestions. Hillrider, I'll make sure and check on this before doing anymore riding; thanks for the warning.

...Yep, grease is totally caked over. Old and faded out. <sigh> The work never ends. <sigh> However, this will represent the final overhaul on the bike, including the pedals, so that's kind of refreshing.