Clogged Rad??

Hello, I have one cast iron standup in my kitchen that does not put out heat.
It is normally cold when all others are warm, and then when my efm is stoking and circulating, it may barely get warm, but not the nice warm we would like to see.

We have different type of rads in the house, and this one seems to have the valve full open,
I have a pic but will need to upload it.

This keeps our kitchen colder, but doesnt matter much.
My coal consumption has been high, so this is one of the problems for sure.
We have a door, so I just been shutting it last few days when we have been eating in the DR with my back to it
and I have found that this would be an easy 10% of my usage.
Since my second floor BR are on the same zone, I know they are an easy 5-10 f higher than first floor and easy 15% WARMER than kitchen @ 60f or so.

The valve is stuck, so before I take a monkey wrench to it....
I had a few questions.

Will opening/closing the valve help unstuck a clog/blockage?
Will taking a wrench damage anything?

For clogged rads, is the only solution taking it out and install a new one?

Thanks
Rob

I will try to get the pick of the valve up soon

Here is the valve

There is the metal piece coming down off the knob, and hitting a stop therefor being full open.

Not sure if the pics are clear enough ..from my phone.

I wouldnt F with it till spring unless I was sure there is a way to valve it off without effecting the boiler system. As far as cleaning out the old radiator you might check with a engine rebuild shop I have seen some downright nasty rust cloged engines come out of a hot tank looking like they were just cast.