A growing iOS bug report now contains two separate iPhone 17 owners describing unusually high temperatures after Diablo Immortal's recent engine update. The original player says their phone becomes noticeably hot within three minutes of launching the game and reaches roughly 40°C externally after around 30 minutes, even while running Diablo Immortal on Low Quality. A second iPhone 17 owner joined the thread on September 5 saying they had experienced exactly the same problem after updating, together with extremely heavy battery drain.
That does not establish that Diablo Immortal's new engine is definitely responsible. Two reports are still a very small sample, and Blizzard has not confirmed a thermal-performance issue affecting iPhone 17 devices. But the matching hardware, timing and symptoms make this more interesting than one potentially faulty phone.
The First iPhone 17 Starts Heating Up in Under Three Minutes
The original bug report was posted on August 26 by a player using a standard iPhone 17 rather than the Pro or Pro Max model.
According to the player, the phone previously became only slightly warm during Diablo Immortal sessions. After installing the recent engine update, however, it began getting noticeably hot in less than three minutes.
The player says they tested the game using Low Quality settings and still measured an exterior phone temperature of roughly 40°C after about half an hour. Closing Diablo Immortal caused the device to begin cooling almost immediately.
They also updated the phone to iOS 26.6.1 without seeing any improvement and specifically asked Blizzard to investigate CPU/GPU load and thermal performance after the engine update.
One hot phone could be hardware.
Then another one appeared.
A Second iPhone 17 Owner Reports the Same Problem
On September 5, another player replied that they had exactly the same overheating issue on another iPhone 17 and that it had also started after the update.
The second report adds another concern: battery life.
The player says Diablo Immortal drained the phone's battery completely in approximately three hours. They report battery health at 89% and argue that the drain is far heavier than they would expect from the device.
Battery runtime depends on brightness, graphics settings, network conditions, background activity, battery health and numerous other variables, so three hours should not be treated as a controlled benchmark.
Still, overheating combined with unusually rapid battery drain is exactly the sort of pattern you would expect if CPU or GPU load has increased substantially.
Whether that increase is actually coming from the new engine remains the unanswered part.
The New Diablo Immortal Engine Is a Major Visual Upgrade
Blizzard has described September's engine update as a substantial technical overhaul rather than a minor graphics patch.
The update reworks visual effects for nearly 100 Legendary Affixes, improves lighting and shadows across more than ten environments, reduces excessive lighting effects and changes ground and water materials. Blizzard allowed players to begin downloading the engine update ahead of the full September launch and even offered 10 Legendary Crests for completing the preparation early.
That is a lot of rendering work being touched at once.
It does not automatically mean the game should suddenly overheat modern hardware. Blizzard's own community team said in August that engineers did not expect currently supported devices to become incompatible because of the engine change.
But compatibility and efficiency are not quite the same thing.
A phone can technically run a game while using more power, generating more heat and draining its battery faster than it did before.
The Engine Rollout Has Already Produced Other Technical Reports
The iPhone complaints also arrive during a period where players are still working through several post-update technical changes.
An Android player using a Galaxy S25+ recently reported that the phone's Back button stopped behaving correctly after the engine update. Instead of closing menus such as the map or inventory, it reportedly minimizes Diablo Immortal and returns the user to the Android home screen. Interestingly, that player says a second phone that had not received the engine update still behaved normally.
We also recently covered players reporting large crafting-resource stacks disappearing around recent Diablo Immortal updates. In that case, as here, there is no confirmation that the engine update itself caused the problem.
These reports should not be combined into one giant “the new engine broke everything” theory. A missing resource stack, Android navigation behaviour and iPhone thermal performance can have completely unrelated causes.
What they do show is that a major technical migration creates a lot of surfaces where strange behaviour can appear.
40°C on the Outside Does Not Tell Us the Internal Chip Temperature
There is another important distinction in the original report.
The player's roughly 40°C measurement refers to the external temperature of the phone. It does not tell us the actual internal temperature of the processor or battery, and it does not by itself demonstrate dangerous overheating.
Modern phones routinely become warm during sustained 3D gaming, particularly when the GPU is being heavily utilized. Devices also have thermal-management systems designed to reduce performance before internal temperatures become unsafe.
The unusual part of this report is therefore not simply “phone gets warm while playing videogame.”
It is the player's claim that the behaviour changed dramatically immediately after the engine update, persists at Low Quality, begins within minutes and is now being independently reported by another owner of the same phone model.
That is what makes it worth investigating.
Lower Graphics Settings May Not Be Enough
The first player's attempt to solve the issue by switching to Low Quality apparently did not prevent the heat buildup. If that report is representative, simply lowering visible graphical quality may not reduce whatever workload is producing the problem.
Players experiencing similar behaviour can still try the usual steps: cap frame rate, reduce resolution and graphical settings, close background applications, avoid charging while playing and make sure both iOS and Diablo Immortal are fully updated.
But if the phone becomes unusually hot within minutes compared with its behaviour before the engine update, repeatedly pushing the device through long sessions purely to see whether it improves is probably not the most useful form of troubleshooting.
A reproducible bug report containing the exact device, iOS version, graphics settings, frame-rate setting and approximate time until the device becomes hot is considerably more useful to Blizzard.
We Need More iPhone 17 Reports Before Calling This an Engine Bug
At the moment, the evidence is suggestive rather than conclusive.
One iPhone 17 owner reports rapid heating, approximately 40°C exterior temperature after 30 minutes and immediate cooling when Diablo Immortal closes.
A second iPhone 17 owner says the same overheating started after the update and reports severe battery drain.
Blizzard has officially rolled out a major engine overhaul involving lighting, materials and visual effects.
Those facts make a connection plausible.
They do not prove it.
If more iPhone 17 users begin reproducing the same behaviour — particularly with comparable settings and before/after measurements — this will become much easier to classify as an optimization problem rather than two unhappy phones.
For now, the new engine is certainly making Diablo Immortal look different.
A couple of iPhone 17 owners would simply prefer it to stop making their phones feel different too.
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