ylod or overheating can be cause by a few variables such as dirty fans and dusty heat sinks or solder joint cracks or an improper flow but seeing as how you'll never know about the improper flow or solder joint cracks its best to assume that its dirty.
so the process of elimination begins get a few cans of air remove cover and all the essentials and spray the heavens out of it wait for about 30-45 mins and spray again wait for another 20 min then power on if all is well then resume playing if not then we have eliminated the dusty inside.
reflowing the mother board can be quite tricky to do applying the proper heat to properly flow the solder joints together again can be a timely and costly repair if done wrong so I would suggest to carefully review about 4 youtube videos about reflowing ps3 mother boards and take the average time they say in all videos total example if video 1 says 15 min video 2 says 25 min video 3 says 20 min and video 4 says 15 min then the average time would be 17-20 min
but once again nothing you are attempting to do is gonna be a guaranteed fix for these systems depending the year they were made has a life expectancy of 8-10 years.