Higher temps might not be registered but I know that if my fan drops below a certain RPM, the computer shuts down. Now, I haven't had that happen (thank god) but if you have good airflow, then the fans might not be doing much anyway.
If your CPU fan is just pushing air into the case, and the case-fans taking the air out, then if the CPU fan is sitting say 3mm above the fins of the heatsink, will you notice a temp difference? No. But there might be a "problem" that your system sees that you don't, so it shuts off to save itself.
My brother had that happen, so he first installed a giant fan at the top (yay for cutting aluminum) which helped a bit. He still couldn't get it to stop shutting down, so he ripped it apart, modified the case, and installed a liquid cooling system. Since then, he hasn't looked back. But he did figure out that it was a fan on his memory I think that was loose, but since he already had the liquid system he just went ahead with the mod.
At least your computer doesn't make the fans jump off their bearings!! My main intake fan, from the original case, went up this past winter. It sounded like the bearing was just needing some oiling, so I took the faceplate off and saw the fan had in fact vibrated itself off its seat and the fins were wobbling as it spun.... mystery of the loud clicking noise (enough to wake you up, and even make you worry) solved!!