MacBook Pro + Thunderbolt = 🔥

Since I replaced my MacBook with MacBook Pro ’13 (2019/Two Thunderbolt 3 Port), I’ve noticed it became hot sometimes when I connected devices to Thunderbolt ports. I don’t like it because it would shorten the battery lifespan.

I made a simple research about this to dig out what causes this problem.

TL;DR

Doing these makes MacBook hot. (Unfortunately, it’s difficult to avoid.)

• Using Thunderbolt port while charging.
• Connecting an external monitor.
• Consuming a lot of power from the Thunderbolt port.

Experiments

I think this problem is caused by the heat of the Thunderbolt controller chip.

I connected several devices to Thunderbolt Ports and recorded Thunderbolt Die’s temperature using iStat menus. I think these sensors’ values represent the temperatures of the Thunderbolt controller.

Remember that my MacBook has only two Thunderbolt ports. Every port is connected to a single Thunderbolt controller.

MacBook Pro 13" Two Thunderbolt Ports 2019 Teardown

1. Without charging

At first, I measured while using the MacBook with its battery.

The first line is a baseline value which measured without any device connected. And the second line is just connecting a USB-C cable. This doesn’t make any difference as I expected.

I tried USB-C to Lightning cable. Surprisingly, just plugging this cable made increased the temperature by 6 degrees. It increased by 9 degrees while charging an iPad.

Idling temperature with USB-C Digital AV Multiport Adapter is the same as Lightning cable. Connecting an external 4K monitor makes a 12 degree increase.

I tried another adapter with several resolutions. Display resolution affects slightly to temperature differences.

Connecting external monitor increases temperatures a lot regardless of the resolution.

2. While charging

Second, I connected MacBook’s charger with USB-C cable to one Thunderbolt port then connected devices.

The first line is a baseline value too. Just plugging a charger doesn’t seem to increase temperature.

But, things get worse when I plugged devices.

It was shocking that just plugging USB-C to Lightning cable while charging increased over 10 degrees. Using 4K monitor while charging also increased over 20 degrees! This is unacceptable.

Conclusion

I thought transferring a lot of data was a root cause of the problem before this experiment. But I found that the combination of charging and transferring from the same Thunderbolt controller is the cause. Maybe this is a problem of the Thunderbolt controller? I don’t know.

How to find cause of high kernel_task cpu usage?

What did I do?

It’s impossible for me to use a MacBook with an external monitor without charging. So my options aren’t many.

As I said earlier, I’m using iStat menus. It’s amazing utility not only monitoring system status but also be able to control fan speed. I created several fan rules to keep my MacBook cool. I feel uncomfortable hearing fan noise sometimes. But this is the best way as far as I know.

I understood providing a lot of power to a connected device may lead to an increase in the temperature. So, maybe replacing the USB hub to another one with self-powered would some help.