Question GPU temp Spike in a second

Dec 30, 2020
it happens 2 weeks ago when my pc boot normaly, but there's no display. and this usually happens because of the power monitor and i already fixed it.
i run kombuster to check and benchmark to see anything wrong with my gpu. this picture below is before benchmark
and this one below if after benchmark

as you can see, and my gpu suddenly has a spike temp from 36 to 90 degrees Celsius. but when i touch the backplate, it doesn't feel 90 degrees at all. it's almost like 30-40 celcius.
so i applied new thermal paste and thermal pad, the results are same from before a sudden thermal spike, and this time it happens when i boot, because my fan immediately have 100% spin.

i try removing bios, ram, also change the pci-e for gpu. but nothing change.
i use HW monitor, afterburner, and GPU-Z to check correlation between those app when i have a spike. and it confused me.

yesterday when my gpu had a temp spike, i immediately turning off my pc and open my gpu, when touch the part that have thermal pad and my GPU processor using a handkerchief it doesn't hot at all.
my last resort is try to reinstall my pc. but i dont want too. because there's to much data to move.

please friend any input will be help for me. (sorry i dont speak english very well)

Thanks in advance
System Information report written at: 12/30/20 19:12:20
[System Summary]

Item Value
OS Name Microsoft Windows 10 Enterprise
Version 1 0.0.18363 Build 18363
Other OS Description Not Available
OS Manufacturer Microsoft Corporation
System Manufacturer Micro-Star International Co., Ltd.
System Model MS-7B45
System Type x64-based PC
System SKU Default string
Processor Intel® Core™ i7-8700K CPU @ 3.70GHz, 3696 Mhz, 6 Core(s), 12 Logical Processor(s)
BIOS Version/Date American Megatrends Inc. A.B0, 05/06/2020
SMBIOS Version 2.8
Embedded Controller Version 255.255
BIOS Mode Legacy
BaseBoard Manufacturer Micro-Star International Co., Ltd.
BaseBoard Product Z370 GAMING PRO CARBON (MS-7B45)
BaseBoard Version 2.0
Platform Role Desktop
Secure Boot State Unsupported
PCR7 Configuration Binding Not Possible
Windows Directory C:\WINDOWS
System Directory C:\WINDOWS\system32
Boot Device \Device\HarddiskVolume1
Intel i7 8700k
Gigabyte 1070 Ti Gaming 8G
Trident.z 8Gb 2x
MSI Z370 Gaming Pro Carbon
EVGA 500 BV 80+ Bronze