t5500 CPU fans won't speed up after CPU upgrade

Hi All,

I have 2 Dell t5500 PCs both had dual CPU E5620. I have 40 and 72 GB DDR3 ram on both PCs respectively. I am using 512 GB SSD on both. Power supply is 825 W on both.

I have upgraded the original CPUs on both PCs, with dual X5670 and another dual X5690. I have also upgraded the heatsinks to two U016F's. I used MX-4 thermal paste for both CPUs. However after the upgrade, the fans do not ramp up under CPU load and as a result the CPU temperature reaches 90-100 C in both PCs. The fans spin at low RPMs.

I have used some programs such as hwinfo32 and speedfan. So all CPU fans on both PCs look OK because if I control the fan using those programs the fans speed up under high load. I can also manually control the fans with no problem using those programs. However I have an issue with those programs as the PC shuts down very regularly and randomly (without any blue screen message) when I am using those programs. Therefore, I would like to figure out a way to make the fans work without using those software.

I have done so many steps. I have re-installed windows 10. I have cleaned the fans. I have restarted the BIOS. But still no luck. I have also used the DELL SupportAssist as well as the start up troobleshooting. Both finish normally without any error, but the temperature during the stress test goes up to 101 C when I monitored them using CoreTemp software. 

My Windows, BIOS and all drivers are apparently up-to-date. In addition, I have re-applied the thermal paste and firmly tightened the heatsinks. Still no luck.

I appreciate any feedback.