ROG Strix SCAR 18 – Still Thermal Throttling and Shutting Down After Full Cleaning, New Conductonaut Extreme + TG Putty Pro. Could the Heatsink Contact Be the Real Problem? PTM7950?
Hi everyone,
I’m looking for some advice from people who own, repair, or have experience with the newer ASUS ROG Strix SCAR 18, especially anyone who has dealt with liquid metal, vapor chamber/heatsink contact issues, or converted their laptop from liquid metal to Honeywell PTM7950.
My laptop is an ASUS ROG Strix SCAR 18 – G835LWG-SA375.
I’ve been troubleshooting serious thermal/performance problems for quite a while now, and at this point I’m starting to believe the problem may not actually be the thermal interface material itself, but rather heatsink mounting pressure/contact with the CPU/GPU dies.
Here is the full story.
Original problem
The laptop started showing serious thermal behavior under heavy loads.
I experienced:
- CPU temperatures rapidly reaching the thermal limit
- Thermal throttling under sustained CPU workloads
- Performance becoming inconsistent under heavy load
- Extremely high temperatures even when the cooling system should have been capable of controlling them
- Sudden complete shutdowns while gaming
These were not normal game crashes to desktop.
The entire laptop suddenly powered off.
This happened to me during demanding gaming sessions, including Rainbow Six Siege, and it also happened multiple times while playing graphically demanding games at very high/Ultra settings.
That was one of the main reasons I started investigating the cooling system.
First thing I did: completely opened the laptop
I removed the bottom cover and eventually removed the entire cooling assembly/vapor chamber.
What I found was concerning.
The factory thermal putty/gap-filler material around the VRAM/VRM areas looked:
- partially melted/deformed
- fragmented
- unevenly distributed
- generally in poor condition
The factory liquid metal on the CPU/GPU also did not look particularly uniform to me.
Some areas appeared to have significantly more liquid metal than others, and I became suspicious that the contact pattern between the dies and cold plate might not be ideal.
So I decided to completely service the cooling system instead of simply closing it again.
Cleaning
I carefully removed the old factory thermal materials.
I used isopropyl alcohol (IPA) to clean the CPU/GPU contact surfaces and surrounding areas.
The factory liquid metal was completely removed.
The old deteriorated thermal putty/gap filler was also removed.
I also thoroughly cleaned the cooling system.
The fans, heatsink/vapor chamber and internal areas were cleaned of accumulated:
- dust
- debris
- cat hair
- general contamination
I also used an electric high-pressure air blower to remove accumulated dust.
The laptop had basically received a much more extensive cooling-system service than a normal fan cleaning.
Thermal materials I purchased
After researching the cooling system, I bought high-end replacement materials rather than cheap thermal paste.
For the CPU and GPU, I bought:
Thermal Grizzly Conductonaut Extreme
For the VRAM/VRM and other components that originally used thermal putty/gap filler, I bought:
Thermal Grizzly TG Putty Pro – 30 grams
My intended setup was:
CPU → Conductonaut Extreme
GPU → Conductonaut Extreme
VRAM / VRM / power components → TG Putty Pro
I did NOT use TG Putty Pro directly on the CPU or GPU dies.
The goal was essentially to restore/improve the factory cooling configuration with high-quality materials.
After reassembly
After everything was cleaned, replaced and reassembled, I expected a significant improvement.
Unfortunately, the fundamental problem is still there.
We then performed controlled testing using Cinebench and HWiNFO.
I specifically tested different ASUS performance profiles.
Performance Mode
During the sustained Cinebench test, the CPU still eventually climbed into approximately the 95°C+ range and started showing thermal throttling.
This was after several minutes of sustained load, not simply a one-second temperature spike.
The laptop could initially look acceptable, but after heat saturation the temperatures would climb and thermal throttling would return.
Turbo Mode
I then repeated testing in Turbo Mode.
Again, I monitored temperatures, CPU power behavior and throttling through HWiNFO.
Despite the more aggressive fan behavior, the fundamental thermal issue remained.
In other words:
New liquid metal + new premium thermal putty + completely cleaned fans/cooling system did NOT eliminate the thermal throttling.
That is what is bothering me.
Why I’m now questioning the heatsink contact
Conductonaut Extreme should not be incapable of transferring enough heat in this laptop.
The SCAR series is already designed around liquid metal cooling.
So if:
- the fans are clean
- the heatsink is clean
- the vapor chamber is clean
- fresh Conductonaut Extreme is installed
- fresh TG Putty Pro is installed
- airflow is not obstructed
…and I am STILL reaching thermal throttling territory, I am starting to think the problem may be more mechanical.
Specifically:
Could the vapor chamber/cold plate simply not be making proper contact with the CPU/GPU dies?
For example:
- uneven heatsink mounting pressure
- slightly warped cold plate
- uneven vapor chamber
- poor factory tolerances
- CPU/GPU cold plate not sitting perfectly parallel to the dies
- one side of the die receiving more mounting pressure than the other
Another possibility I’m considering is the thermal putty itself.
TG Putty Pro is obviously not a bad product.
But I’m wondering whether too much putty on one or more VRAM/VRM components could prevent the vapor chamber from fully seating against the CPU/GPU dies.
Even a very small difference in height could potentially matter because liquid metal is meant to create an extremely thin thermal interface.
If the cold plate is being held slightly above the CPU die because another component/putty layer is resisting compression, adding better liquid metal obviously would not solve the actual problem.
This is also why I am considering PTM7950
Several people I’ve talked to online, including other gaming-laptop/ROG users, recommended that I stop using liquid metal and try:
Honeywell PTM7950
I know PTM7950 does not have the same theoretical thermal conductivity advantage as liquid metal.
That is not really my point.
My thinking is that PTM7950 may create a more consistent real-world interface if my laptop has slight imperfections in:
- mounting pressure
- flatness
- cold-plate contact
- thermal expansion
- die-to-heatsink alignment
I’ve seen multiple laptop owners say that they actually obtained better and much more consistent temperatures after replacing liquid metal with PTM7950.
That makes me wonder whether liquid metal is simply exposing an underlying contact problem in my particular unit.
What I’m thinking about trying next
My next configuration would probably be:
CPU → genuine Honeywell PTM7950
GPU → genuine Honeywell PTM7950
VRAM / VRM → Thermal Grizzly TG Putty Pro
and completely removing the liquid metal.
But before doing that, I’m also thinking about inspecting the contact/imprint pattern very carefully.
For example, mounting the heatsink once and removing it again to see whether the TIM compression pattern is even across the entire CPU/GPU die.
If one section shows significantly different contact than another, that would probably indicate a heatsink pressure/flatness problem rather than a TIM problem.
My questions for SCAR 18 owners / repair technicians
Has anyone with this generation of ROG Strix SCAR 18 experienced the same thing?
Especially:
- persistent CPU thermal throttling despite replacing the liquid metal
- strange or uneven factory liquid-metal contact
- poor heatsink/vapor-chamber mounting pressure
- warped or uneven cold plates
- excessive VRAM/VRM putty affecting CPU/GPU contact
- sudden power-offs during heavy gaming despite apparently normal operation beforehand
And most importantly:
Has anyone converted a SCAR 18 from liquid metal to genuine Honeywell PTM7950?
If you did:
- Did temperatures improve?
- Did CPU temperature become more consistent?
- Did hotspot/core deltas improve?
- Did thermal throttling disappear or decrease?
- Did sustained performance improve?
- How has PTM7950 held up long-term?
- Did you also keep thermal putty on the VRAM/VRM?
- Did you notice an uneven contact pattern when removing the factory heatsink?
At this point I don’t want to simply keep buying progressively more expensive thermal materials.
Conductonaut Extreme is already one of the better liquid metals available.
If fresh Conductonaut Extreme cannot solve this, I think I need to determine whether the actual problem is the physical interface between the dies and the vapor chamber.
I’d especially appreciate input from anyone who has personally opened and repasted/repadded this exact generation of SCAR 18.
If you have before/after HWiNFO screenshots, Cinebench results, mounting/contact photos, or PTM7950 results from the same machine, I would really like to compare them.
Thanks.