I recently built my computer inside a smaller mid-tower case, replacing my old 420mm AIO cooler with a 280mm Arctic LF3 model. After 30 years of building PCs, I'm faced with a frustrating issue. The system idles at a comfortable 30°C, but when I run Cinebench R23, the temperature jumps to 100°C almost instantly, causing throttling. In my previous setup, I could run at 253W all day around 70°C without any issues, and I know I could push it over 300W without throttling. Given that the temperature spikes so quickly, I'm not sure if it's a cooling issue since the plastic cover was removed and the pump seems to be working fine. Could there be a flow issue in the radiator? I'm completely puzzled by this situation.
2 Answers
Check the size of the copper part of your cooler. The issues you're experiencing could be due to either poor contact or the heatsink not being substantial enough to dissipate heat effectively. I've had a similar issue where incorrect torque on the waterblock mounting caused problems. Also, consider if your AIO is defective—no fluid or a bad pump could be the culprit. You might want to shake the radiator; if there's too much sloshing, it could mean there's too much air in the loop.
It sounds like you're dealing with a contact issue rather than a cooling problem. Have you checked if you're using a contact frame? 14th gen CPUs have a tendency to bend and may not be making proper contact with the cooler.

The Arctic LF3 comes with a proprietary contact frame, so that shouldn't be a problem. But if the water isn't flowing well, that could definitely cause the quick spike in temp, right?