I was troubleshooting a stuttering issue and decided to replace the CPU thermal paste to rule out overheating. Before doing that, idle temperatures were around 40°C, but now they sit at 65–70°C and reach 100°C during gaming. I'm using an AIO liquid cooler. Its fan spins, and one tube feels hotter than the other, so I assumed the pump was working. I've already reapplied the paste, but the temperatures haven't improved. What's the best way to determine whether the pump, cooler mounting, or something else is causing the problem?
4 Answers
A 100°C CPU temperature strongly suggests the cooler isn’t transferring heat properly. The AIO could have a dead or damaged pump, a blockage, or an air pocket. Check the motherboard BIOS or monitoring software for an RPM reading from the CPU_PUMP header and confirm that the pump is actually powered. A large temperature difference between the tubes can also indicate poor coolant circulation, although tube temperature alone isn’t definitive.
You can also try starting the system with the case lying flat, then gently repositioning it to help move a trapped air bubble. This is only a test, though—not a fix for a failing pump or a blocked AIO. If the pump has no reliable RPM reading or the temperatures remain at 100°C after remounting, replacing the cooler is the sensible next step. A large tower air cooler is often cheaper and simpler than another AIO.
Since the problem started after the paste was replaced, remove the cooler and check the contact pattern on the CPU and cold plate. Make sure the protective film is gone, use a reasonable amount of paste, and tighten the mounting screws gradually in a cross or star pattern. The cooler should be firmly and evenly secured; paste cannot compensate for poor contact.
Verify that the pump cable is plugged into the correct CPU_PUMP or AIO_PUMP header and that the header is configured to run continuously at the required speed. Also check that the CPU fan or pump wasn’t accidentally unplugged while the paste was being changed. Avoid heavy gaming or stress testing until the cooling problem is resolved.
If the pump checks out, inspect the block mounting next. Even a small gap or uneven pressure can cause temperatures to jump this much.