YLOD fix, but system still overheats very rapidly

My PS3 broke down about 3 years ago and I just found out about the YLOD fix kit. I got it today, did the repair (replaced thermal paste, pads, cleaned dust out, etc..) and started to play it. It was working well until I opened up a game (LBP2) and then it died out after only 10 or so minutes of play. The light was flashing red, I think a sign of overheat? I’m wondering why it’s overheating so quickly after I just repaired it? The fan was running full-bore and the machine was very warm to the touch. Should it really be overheating that quickly?

To give an idea, it’s a backwards compatible first model, in an open, ventilated area. The room is about 68-71 degrees. Idk if that is pertinent.