What do you guys suggest I do about this?
Drain, flush with water,refill /water, run car,then drain and refill with a good antifreeze.(providing system is OK.)
Andrew, 30 years is a long time for any fluid that is in your radiator/engine. Can you elaborate more on what you can see? Is there any trace of anti-freeze, or is is just a brown rusty mess? In any case, take Jacks great advise and give it a good flushing, i personally would pull the head and make sure all the cooling ports in both the block and head are free and clear as well, and not blocked by any rust.
Andrew - MY 19 sat for about 46 years with fluid in the radiator.
I drained it,filled the system with vinegar, and let it sit for a few days. Then I removed the bottom hose and flushed it and the block with clean water. (I tried to use the petcock but it kept plugging.)
I believe that the antifreeze/water mixture helped protect the motor.
If you have a brass T, I strongly recommend NOT using antifreeze. If it gets on the brass, it stains it, and is all but impossible to remove.
Mine sat for some unspecified length of time (there was a 1970's quarter on the keychain - take that as you will) with some mystery mix in the rad before I got it. I sent the rad off for a hot-tanking and patch job as required and flushed the water jackets out with a hose. The stuff that came out ran the whole spectrum from green to orange to rust to brown sludge. After the hose I decided to got at it with a pressure washer jammed down into the head and even more gunk came washing out. As a part of going over everything I also pulled the head and while it was off I ran a piece of bicycle brake cable in a drill (frayed on one end) to further clean out the passages. For some of it I set up my shop vac as a sort of collection system. Amazingly, even more crud came out but this time it was all sorts of fuzz, flakes, small twigs, pine needles and whatnot. Oddly enough, it came with a rad cap as beat up as the rest of the car so I have no clue how that stuff got in.
So from my experience I would say clean the hell out of it unless you know exactly where it's been these last thirty years.
"30+ years sitting with fluid in radiator"
What kind of fluid?
Its been sitting in a garage/basement for the past 30 some years and it appears to have an anti-freeze/water solution in it.