Cheapest i ever did it was in 1997 with a cheap submersible pond pump (220v/240v) tubing from a diy store and clips etc etc and a van heater-core matrix from a scrappy (brass rad)
(memory pricing estimate at the time) Worked fine and cost at a guess £60 for all clips etc then on top a danger den maze i think it was for £30 so all in all just under £100
Would i do that scrapheap challenge today ?? Err no
Had a massive tower with a tupperware round tub in it with the pump in, My rad (heater-matrix) was not fitted anywhere so was at the side or rear of my tower and was a pain for collecting dust/fluff, I also had no time or inclination to tidy this up so i plasic welded 9 80mm fans together and taped those over the rad lol
Ohh and then my 2nd psu (a spare i had) ran the pump, so i had to switch both psu's on to power up (i know some wiring could have made it 1 switch but i never) must add i did have temp probes all over the place as water was new to me, Left pc on once and switched pump off and the res (tupperware was hot to the touch after 12hrs but never went on meltdown lol) (can't rem exact temp but water felt hotter than lukewarm for sure)
I got this kit after looking to get back into water cooling
http://www.overclockers.co.uk/showproduct.php?prodid=WC-014-SW&groupid=701&catid=193&subcat=1038
How i decided was looking at reviews and reading forums etc, Then when i priced a singularly itemised setup (my choice of pump/block/barbs/rad/res/tubing etc etc) i was over what the kit cost then different postages etc and time waiting for all bits that were out of stock etc
Then there's how/where to mount the rad etc, But with the kit it's there made out of plastic so it's light and fits great and looks properly done
After these considerations that's why i went for a kit to get me back into things
I am sat 8inch from my room radiator on my left and today like most days i have the room stat at 22c (i know i likes to be warm)
My tower is just over 3ft from the rad and at the moment she's running at 34c-36c idle Core reading 50c according to everest or core temp (not used together)
Just started prime to check 100% cpu load temps and my quad 6600 @ 3.2 is between 47c/50c Core is reading 63c and case/mobo reading 34c (EDITED: Fans on rad are on 7v not 12v, 12v cools more but obviously slightly louder, Thought i best add this info)
Cheap can be done, Does it work ? Hell yes i found that out many years ago
Best bet for people more in the "know" would be to bite the bullet and put your maximum outlay here and let the water guru's pick over and come up with suggestions
Sorry to waffle on lol
Ciao
Def
