Tying PWM fans to coolant temps on the cheap...possible or not?

Greetings humans!

I have a question for the water cooling gurus: is there any way to tie PWM fans to coolant temperatures in a custom loop without having to fork out a silly amount of money for an Aquero? I just started toying with PWM recently (tardy to the party), and being on an older platform (x79), I am of course relegated to CPU temperature for this, which is useless. I have the temp sensors, but no clue how to link the two.

Any ideas? TIA!

Not sure how good you are with coding and how much you want to DIY.
One option:

Using something like this to controll:

And the sensor (thermocouple):

Holy cow, thanks for the advice! That's a bit (err a lot) over my head, but that's a very interesting idea. I've been telling myself for years that I need to get into stuff like this (bread boards, etc), so maybe this is the excuse I need to take the plunge. Thanks much!

Some motherboards have inputs for additional temp probes. If you find one compatible with your motherboard and water resistant you can run it down the reservoir and be done.

Or you can boot the system, write down the temps of the cold system and measure somehow the fluid temp. Than do the same for the highest load possible with a synthetic load on everything. Take note of the temps of the components and the fluid as they warm up. After you're done you'll have a one to one curve of the fluid related to the component temps. You're done, with much hassle but for absolutely nothing (if you don't take into account time = money).

P.S. you can maybe smooth the curve out with some math, if you know how to make an approximated curve having a set of points.

Hmmm, not sure if that would work though. With a custom loop, the component temps don't rise in a gradual curve (as you probably know). They just shoot up to almost their maximum (in my case, 45C-48C), and climb very slowly from there. The liquid temps are a much more gradual curve. When my CPU maxes out in terms of temps, it's at about 55C. Once it hits the max, the liquid temps continue to climb steadily, until they reach their max (not sure what that temp is since I haven't really tested that). So trying to tie PWM stuff to component temps doesn't really work too well.

Thanks for replying though, I really appreciate it!