Acer 5720z overheating and shutting down

Symptoms: You are happily working away and suddenly it just dies on you. Half and hour later after it has cooled down it will work again.
This seems to be quite common so I thought I’d post this as its not mentioned in the repair manual.
I had already checked around the web for a way to get into the laptop which sounds quite easy but having never opened one up before I was cautious. This is how I got to the fan.
Step 1. Power off
Step 2. Remove battery
Step 3. Unscrew harddrive and remove (I don’t know why but it may add some more flexibility in the frame
Step 4. Remove 4 screws for the central panel (odd shaped one) on the back of the laptop
Step 5. The hard bit now; the panel just won’t come out naturally, you will need a flat hard piece of plastic, preferably a flathead screw driver or something similar. Pull up the panel where the finger dent is and slide the plastic implement carefully around the edge. I had to be quite forceful. You get the impression that there are more screws somewhere but there aren’t. Eventually one of the edges will snap. Start from the finger hole side. Hooray it comes off eventually. It is equally hard to get back in by the way.
Step 6. There is the fan. Unscrew the 3 screws holding it. Make sure you don’t break the cable moving it. My intake had a good deal of dust that you can get rid of carefully.
Step 7. My machine was fine afterwards. I put speedfan (¬†on to check the core temperatures. But it hasn’t shutdown yet.