If this has been covered I apologize but, my search turned up nothing.
My question is, is there any way to tell if the coolant cap is shot? I mean, not by the overheating but by it's physical appearance or something like that. ???
Thanks for any help you may be able to provide.

 

You would have to pressure test it. But you can purchase one for under $20.

I purchased one from Oreilly's for $17 and some change with tax.

Murray Caps & Stats 7042 - Standard Radiator Cap 2000 Land Rover Discovery | O'Reilly Auto Parts

 

Yes, just look at the inside of it, is it cracked, falling apart, is the 0-ring missing if so get rid of it. The other end would be your mileage, at 100,000 miles plus it would be $17 worth spending.
Are you having an over heat issue?

 

Yes, overheated on me the other day and now has coolant in one cylinder. I'm going to tear it down later on today and see what I can find. As far as the cap goes, it doesn't appear to be bad, no cracking, good o-rings, etc.
It only overheated for maybe a minute at the most but, did have some coolant mist inside the oil filler cap, only after I shut it down and it sat for a minute or so, there wasn't any in there when I first looked but built up in there shortly after overheat. There doesn't seem to be any in the bottom end (no milkiness to the oil) just a bit up in the top end. Not sure of the cylinder # but there was coolant on the third plug from the front on the driver's side.
I'm not sure if the overheat occured due to the head gasket or if the coolant leak occured due to the overheat but, I guess it doesn't matter now as I have to replace the head gaskets at a minimum.

 

Let us know what you find.