Sudden shutdown and then overheating

I have a MacBook Pro 15" approx 2 years old. Past few months it has suffered with sudden shutdown for no reason, plugged in , fully charged. Recently though symptoms have changed. Sudden shutdown occurs with black screen. Up to this point the computer has been running cool. Now, after sudden shutdown, the computer starts to heat up and becomes too hot for comfort. It just won't restart. Has been to the Mac authorized repair shop x 3 and that have told me there is nothing they can find. I work in remote areas and need reliability for access to critical information for patient care. Any ideas?

Immediate thoughts that come to mind are degraded thermal paste around the CPU, internal fans not working, and to much dust inside the casing. Repair shop should have spotted all of those just about immediately.

The device is definitely overheating, probably the CPU, though some other part could be generating to much heat and warming everything up. Obviously, I cannot say for sure that's the problem but here's an article talking about repasting a Macbook CPU. It isn't hard but might be a little daunting if you've never done it. I'd be suspicious of the shop you have been going to if they can't figure out an overheating issue. If a repaste doesn't fix the problem (because something else is generating the heat) then it may at least help combat it.

The shop ~should have~ blown all the dust out of your laptop if they bothered to crack it open but make sure you have a can of compressed air and blow any dust you find out yourself as well.

It could be CPU paste but in a two year old machine? Unless you are operating it in extreme conditions it would not my first choice. It almost sounds like fan failure. Macbook Pros will run warm but when they get too warm a system fan kicks in. You should be able to hear the fan working and if it is then that is not the issue. If not it could be the fan died or a sensor has gone bad and is not signaling for the fan to run.

Can the repair person reproduce the issue? It is very hard to figure out a problem without actually seeing the computer reproduce the error.

Lisa

Thanks for the helpful and thorough replies. I don't mind operating on humans, but opening a mac would be be beyond my skills!
The symptoms are not being reproduced in the repair shop. They have been very good and haven't charged anything even though they have spent a good few hours working on the computer over three separate visits.
In the shop, the tech runs the computer on his work bench. He had no problems after running for hours. As soon as I put the Macbook on my knees, it quit. Restarted once, then quit again and would not restart until this morning, 16 hours later. When it quit last night, the power cord was attached and the charge state was 100%. When it restarted this morning, the charge state was 0%. Shortly after it shut off last night, the computer base (towards the screen in the middle) became hot and stayed so for an hour or so. Given the recurrence of shut down with position change, I wonder if the case could be shorting out. Whatever happened, drained the battery completely. Any further thoughts would be helpful. Thanks again