Precision 3620 i7-7700 3.6GHz - Fan Speed Haywire!

Not in BIOS, at F12 boot selection menu, select diagnostics and immediately hit Esc key twice to display the test progress.  The fan(s) provides RPMs for low, high, and current.  That should give you an idea of which one was running abnormal.

There is a fan tucked between the cooling fins of the CPU cooler as pictured below.

Dell's Pre-boot Diagnostics is built-in tool for testing.  F12 at boot to select diagnostics.

Users popular third party apps such as HWMonitor often suggested.

Speccy is a free app that gives you a peek into your overall system specs, including temperatures.

Usually, there are 4 fans to check, CPU fan, rear case exhaust fan, video card fan, and power supply fan.

Hi again Chino!

I just ran the Diagnostic Test: 'No Problems Found' (and) to add to the mystery, after the test, the machine booted back up: (no more erratic fan speed)?

There is no Video Card (I'm using onboard video ). Using a sound card, but no fan. And the CPU has that GIANT copper Cooler, (Only Two Fans Total) ...

This 'Could' still be an 'intermittent' problem? Wonder if it could STILL be either the Power Supply Fan (or) the Case  Fan?

Thank You!

Hi Chino

I actually followed the test progress twice now ... Neither test showed 'Erratic Fan Speed'

Is there an App that will provide 'fan speed monitoring' in 'real time' and identify each fan?

BTW Thank you for the clarification of the little CPU 'sandwhich fan'

Thank You ...

Thank You

You may try the HWMonitor linked at first post.  Do not try to change any fan curve yet, just to view the info you are looking for. 

Hello Chino

Tried to download and install HWMonitor - All kinds of 'Bloatware' initially appeared - Anyway here's a few screens. I'm not sure what to look for? As mentioned, the erratic fan speed disappeared after I ran W10 Diagnostics .... uhm? Where do I find identification of the Fans?

Thank You  Chino!

Those hardware monitoring apps are just reporting information from machines sensors it can "see" and connecting to.  Some machines get better reports than the others.

It seems that it didn't report any fans for your system, uninstall it and try HWiNFO.