iMac 27" 2020: RAM Upgrade and Thermal Service
Overview
A video production company from Bella Vista brought in their iMac 27-inch complaining of slow performance and loud fans during editing work. The base 8GB RAM was insufficient for 4K video editing, causing constant memory pressure. Additionally, thermal paste had degraded, causing the system to throttle. We upgraded the RAM to 64GB and performed thermal service, completely transforming the machine.
Initial Symptoms
- Severe slowdowns during DaVinci Resolve timeline scrubbing
- Rainbow wheel appearing frequently during editing
- Fans running at maximum speed during light work
- Activity Monitor showing constant memory pressure (red)
- System using 15GB+ swap space
- Machine was only 4 years old
Diagnostic Process
Memory Analysis
Monitoring memory usage during video editing:
- Physical RAM: 8GB (fully utilised constantly)
- Swap usage: 15-25GB during 4K timeline work
- Memory pressure: Sustained critical (red) level
- Application demand: DaVinci Resolve requesting 20GB+
Thermal Analysis
Temperature monitoring revealed additional issues:
- CPU temperature: Hitting 100°C during renders
- Thermal throttling: CPU reducing from 3.8GHz to 2.5GHz
- Fan speed: Maximum (2700 RPM) even at idle
- Root cause: Degraded thermal paste + dust accumulation
Recommendations
Two-part solution proposed:
- RAM upgrade from 8GB to 64GB (user-accessible on this model)
- Thermal maintenance: paste replacement + cleaning
Upgrade and Service Process
RAM Upgrade
The iMac 27-inch 2020 has user-accessible RAM slots—one of the last iMacs with this feature:
- Accessed RAM door on rear of iMac
- Removed factory 8GB (2x4GB) modules
- Installed 64GB (4x16GB) DDR4-2666 modules
- Verified detection: System Information showed 64GB
Thermal Service
Required opening the display for internal access:
- Removed display using suction cups and heat
- Cleaned significant dust from fans and heat sinks
- Removed old thermal paste from CPU and GPU
- Applied fresh high-performance thermal compound
- Reinstalled display with new adhesive strips
Results
| Metric | Before | After |
|---|---|---|
| Available RAM | 8GB | 64GB |
| Swap usage (editing) | 15-25GB | 0-2GB |
| CPU temp (render) | 100°C | 78°C |
| CPU speed (sustained) | 2.5GHz (throttled) | 3.8GHz (full) |
| Fan speed (idle) | 2700 RPM | 1200 RPM |
Outcome
The video production team reported the iMac now handles 4K editing smoothly with no rainbow wheels. Timeline scrubbing is instant, renders are faster, and the fans are finally quiet. The upgrade extended the useful life of this machine significantly.
Key Takeaways
- Base RAM is often insufficient: 8GB isn't enough for professional creative work.
- iMac 27" 2020 RAM is user-upgradeable: One of the last Macs with accessible RAM slots.
- Thermal maintenance matters: 4-year-old thermal paste can significantly impact performance.
- Upgrades extend machine life: A few hundred dollars in upgrades saves thousands on replacement.
iMac Running Slowly?
RAM upgrades and thermal service can transform older iMac performance. Ask about upgrade options.