While you were dissembling your laptop, Did you remove heat sinks then clean old one and put new Thermal Grease? If not!?, be sure you do it in right way! (Do not put too much of it! just check youtube videos)
Also be sure your cooler fans work properly. You can use any Free Hardware monitoring programs. (like: Open Hardware Monitor or 'SpeedFan' or Aida64 ...) Then make stress on your processor and watch fan speed reaction to processor heat!? (Aida64 have some stress functions to test hardware's)
General Rule: If you have your laptop for a long time or use it anywhere you go!? And If while you were cleaning it, you found out too many dust inside it, It will be a good idea to change all Thermal Grease under heat sinks. (This rule, even applies on Desktops too! Base on work area conditions, Cleaning Fans and Changing Thermal Grease after 6 months or 1 year.) Also sometimes we have to replace some fans too! Cleaning fans also have its own technique, The safest way to clean it is to use Blower on it. But if you gonna use brush on it make sure you know how to do it.