Why is one CPU core much hotter than the others at higher overall temps?

[dbookbinder]

The i7-1355U CPU on my HP Laptop 17 c3000 has two power cores and eight efficiency cores. The second power core is always hotter than the other by about 10-15C, once the temps go above 60C. (Below that, they are about the same.)

One explanation could be uneven application of thermal paste, but because the computer is only a year old, before I mess with reapplying thermal paste -- which I've only done once, 20 years ago -- I'd like to confirm that this isn't normal behavior for this CPU. Anyone out there who can help me with this?

[A_Gayathri]

Hi @dbookbinder,

Welcome to The HP Support Community.  

Thank you for posting your query, I will be glad to help you.

I understand you want to know if the CPU core is much hotter than the others at higher overall temps
 

It’s common for one CPU core to run hotter than others, especially in newer processors with a mix of performance (P) and efficiency (E) cores like your Intel i7-1355U, which has 2 P-cores and 8 E-cores. However, a 10-15°C difference between your P-cores at higher temps could be indicative of a few things. Before reapplying thermal paste, let’s go over possible reasons and actions:
 

Reasons for Core Temperature Disparity:

1. Task Scheduling: The operating system may assign more demanding tasks to one of the P-cores (often the primary one) over the other, causing it to run hotter. This is especially noticeable under high workloads.
2. Thermal Design & Distribution: The cooling system or heat distribution can be uneven, particularly in laptops where space is constrained, which can result in one core being closer to a hotter component (like the GPU or another heat source).
3. Thermal Paste Application: While unlikely in a relatively new laptop, an uneven application of thermal paste can cause uneven heat transfer between the CPU and the cooler.
4. Power Delivery and Boosting: One of the P-cores may be boosting higher than the other under load due to power management behavior, which could explain why temperatures diverge above 60°C.

Actions to Consider:

1. Monitor Core Usage: Use a tool like HWMonitor or Intel XTU to track CPU frequency and load for each core. This will help determine if one core is consistently doing more work or boosting higher than the others.
2. Check for Throttling: Ensure that the CPU isn’t thermal throttling under load, which would cause temperature increases and uneven core behavior.
3. Update BIOS and Drivers: Ensure your BIOS and chipset drivers are updated, as updates can optimize power and thermal management.
4. Fan & Airflow: Clean the fan and ensure proper airflow. Blocked vents or dust can exacerbate temperature differences across cores.
5. Thermal Paste (Last Resort): If monitoring shows no irregularities, but the temp difference remains, and the laptop runs hotter than expected under load, reapplying thermal paste could help. If you’re not comfortable doing this, professional service is recommended.

Normal vs. Abnormal:

• Small temperature differences between cores, especially under load, are normal due to task scheduling and heat distribution.
• A consistent 10-15°C difference at higher temperatures is notable, but if it’s not causing thermal throttling or performance degradation, it may not be a cause for immediate concern.

Before going ahead with the thermal paste reapplication, try to gather more data on core usage and task distribution, as it might just be normal CPU behavior.
 

Refer to this document: HP 17.3 inch Laptop PC 17-c3000 (767L6AV) User manual 

I hope this helps. 

Take care and have a good day.

Please click “Accepted Solution” if you feel my post solved your issue, it will help others find the solution. 

[dbookbinder]

I have already done the monitoring, cleaning, and related steps you describe. The computer does frequently throttle under load. When I monitor the temps, it's always the second power core that overheats. When I compare temperatures to what cores are active, it looks as though the two power cores are about equally active, but the hot core is always much hotter once temps get about 60. This seems to happen with apps that don't utilize all the cores. It seemed to me that either 1) this is just the way the i7-1355U CPU works and there's nothing I can do about it, 2) there is a design issue with this particular chip, or 3) the thermal paste was misapplied at the factory and there's a bit of grit or an air bubble that's causing the discrepancy.

If somebody with this same CPU can check their computer's temps under load, that would be definitive. 

[A_Gayathri]

Hi @dbookbinder,

Thank you for your response, I appreciate your efforts. As the issue persists, I am sorry to hear that I'm sending out a private message to assist you with the next course of action. 

Please check your Private message icon on the upper right corner of your HP Community profile Next, to your profile Name, you should see a little blue envelope, please click on it or simply click on this link.

I hope this helps! Keep me posted for further assistance.

Please click “Accept as Solution” if you feel my post solved your issue, it will help others find the solution. Click the “Kudos, Thumbs Up" on the bottom right to say “Thanks” for helping!