What's happening with my fan?

Today I was going through the routinely PC cleaning and I've found what looks like a pretty bad thing. I took off one of the fans from my NH-D15 and inside the frame of the fan I've found what looks like bearing fluid spilled all over it. I got a bit worried and started moving the fan on my own to listen for any weird noise or resistence of any kind but the fan it's still spinning perfectly and little to no resistence (even with a little hit on the blades the fan spins for quite a lot). I still have 5 years of warranty on them so what I should do: contact Noctua to get a new fan right now or wait until it dies (or the warranty is about to run out)? Thanks for all the answers.

The sooner you replace it the better.

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If your fan bearing did spring a leak, certainly get it replaced ASAP.

A fan will still operate without bearing fluid, but the bearing will quickly deteriorate due to friction and heat from all the movement.

Thankfully, Noctua heatsinks have clips that allow for interchangeable fans, so if you have a spare lying around, that will do for the time being, while you are getting a replacement.

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Yeah, sounds like a fluid dynamic fan that has lost its lubrication. Eventually it will melt through the plastic.
Replace it.

Contact Noctua ASAP and get it replaced. Considering how they claim to care about quality, I imagine that they'd be pretty interested in finding out what happened.

If your case has enough airflow, you may well be able to run it without the CPU fan for a while. Just keep an eye on the temps at first and don't benchmark it extensively.

As far as I know, the NH-D15 ships with 2 fans. Having one in the middle should be enough to keep temps in check.

I have two fans on it so I can run it with even just one fan in the middle (the Noctua NH-D15S is shipped with a single fan so I guess is intended also to run with a single fan). Yeah, fortunately I bough a nice case so airflow won't be a problem.

Thanks to anyone that replied. Just one issue guys: summer vacations are on the edge of beginning so sending out the damaged fan right now means wait until september to get a new one.

P.S. is it possible that my motherboard (Asus Maximus VII Hero) pumps a bit too much voltage through the header the damaged fan is conneted to and that caused the damage? It's just a fluid leak and, when I checked through hwmonitor, the CPU fan speed looked alright (around 1500rpm max).

After cleaning the fan, in two days, no more leaks have been seen.

Nah, there's almost zero chance that the fan is getting more than 12V. CPU fans use PWM (Pulse Width Modulation) instead of voltage control, meaning their RPM is controlled by giving them power in very short or slightly less short bursts rather than by actually changing the voltage.
Even with 12V all the time, the fan should be able to last several years (Noctau gives the fan a MTBF rate of ">150.000 h", which is around 17 years).

The NF-A15 fan uses 140mm mounting holes, so in the unlikely event that you'd see a massive difference in CPU temps you could substitute any 140mm case fan that you may have laying around.

Good to know. I was just wondering if that could be a possibility. I'll try to send to Noctua the fan as soon as possible (hoping they won't ask for the whole cooler, that would make me crazy and my 4790K melting hot lol). Thanks!