I've been looking into PC cooling problems where GPU and CPU temperatures are significantly higher with the case completely closed.
In one example, the GPU was reaching the high 80s under full load and the CPU was around the high 70s. After removing the tempered-glass side panel, both temperatures dropped considerably, with the GPU falling into the mid-60s.
The case had very limited airflow, no mesh front and only a single rear fan.
Would a temperature difference that large with the side panel removed be a strong indication that the case itself is restricting airflow?
And in a situation like this, would moving the components into a basic mesh-front case with three front intake fans and one rear exhaust fan likely make a significant difference, or should other cooling problems be investigated first?
A large temperature drop when removing the side panel is a very strong indication that case airflow is contributing significantly to the problem.
The important clue isn't simply that the GPU reaches the 80s. It's what happens during the side-panel test.
If the GPU drops from the high 80s to roughly the mid-60s under similar load after removing the glass panel, the GPU cooler has demonstrated that it can cool the card much more effectively when supplied with cooler outside air.
With a closed case that has almost no front ventilation and only one rear fan, hot air can accumulate inside the chassis while the GPU and CPU repeatedly recycle warmer internal air.
A mesh-front case with three front intake fans and one rear exhaust fan would normally provide a much better airflow path:
Cool air → front intake → CPU/GPU → rear exhaust
So before spending money on a new CPU cooler or attempting more aggressive solutions, improving case airflow would be a very reasonable first step.
A used case isn't automatically a problem either. If the friend's case is structurally sound, the fans work, the front mesh isn't damaged, the required components fit, and the price is significantly lower, its age alone wouldn't prevent it from providing better airflow.
I'd still check:
• Dust buildup on the GPU and CPU cooler
• Whether all fans are actually spinning correctly
• Fan orientation
• GPU fan curve
• CPU cooler mounting
• Ambient room temperature
But the side-panel temperature comparison is the strongest clue here.
If anyone is diagnosing a similar problem, test temperatures under approximately the same workload with the case closed and then with the side panel removed. A dramatic improvement with the panel removed points strongly toward restricted case ventilation.