Intel CPU 100 degree temperature

Hi,

I have following case Desire | Cabinets | Intermediate | Zebronics - Always Ahea (many pics there of it's inside)

Recently got my intel stock cooler replaced by intel .
Now I am getting very bad cpu temp under load.
Cpu temps reaches near 90-100 degree within 2 min.

I have tested this with Handbrake and plex encoder only. Even a bit load in chrome causes temp difference by 5-10 degree.
But as soon as cpu goes to idle temp stays at around 35 degree.i can't figure out whats wrong.

The stock cooler came with pre applied paste so i didn't bother removing it. And i have made sure heatsink is tightly seated .

** The only thing i can feel is not enough air is going out the case, i have no rear case , earlier i had zebronics psu and I could feel hot air going out if i put my hand behind the case vent. Now i have corsair psu and i can hardly feel air (very low amount air) going out through back.

P.s . I have two side intake fan only

Any idea what could be wrong ? I don't think i can put a rear exhaust fan on my case.. should i make one of the side fan pulling air out?

Thanks

System configuration? How did you make sure the heatsink is tightly secure? Thermal pastes wear out at some point depending on the age and the amount of heat it needs to dissipate. With limited info, is all one can say.