Land Rover Repair: Coolant system

Question
QUESTION: Good day Mr.robison I hope this finds you well. I have a 2000 land rover discovery 2. The other day I left the coolant cap off of the reservoir. It started running hot so I pulled over to let the truck cool down. As I was leaving I noticed a large coolant spot on the ground, truck starting running hot again. The coolant cap was off for about a day. I refilled, and put the cap on tight. Is it possible that I have introduced air into the system, and need to bleed it? Have i damaged the thermostat? Your thoughts would be most welcomed. Thank you.

Regards
Kenneth

ANSWER: It sounds like you have an overheating problem.  Opening the cap won't introduce air into the system but boiling over might.  However, the truck would not have boiled over in the first place without some other problem.  Look on the Robison Service blog and on my website for more extensive articles on Land Rover V8 overheating.  

As these truck get older, more and more of the overheating issues stem from internal engine failures

---------- FOLLOW-UP ----------

QUESTION: Thanks for your reply Mr. Robinson.
I have one more question. Occasionally I should say very infrequently i would be out driving, and out of nowhere my vehicle would go from normal to hot. I would pull over at a gas station, check under the hood, no apparent leaks, no steam, no apparent reason. I would start the vehicle up, it's now back to normal, and would stay that way for months, reoccur, same scenario, same results. 2 years ago I had a lot of work done by a very reputable rover mechanic, I was having the air bags replaced, I also had him look into the hose leading to the thermostat, it had a history of sliding up off of the thermostat. He replaced the clamps, the truck ran well for about 23 months until now. I always try to find the simplest solution first. Should the first thing I should look at is a failing thermostat? Thank you for your time and advice. By the way I did look up your website and blog.

Regards
Kenneth

Answer
I am afraid your story sounds like an internal failure in the engine.  I had referred you to my several articles on that and I think a small but growing crack in the block is the root of your trouble, given that you've tried all the common external remedies