Bacteria & Gas buildup in Watercooling System (w/Pics)


Apr 1, 2009
Hey Watercoolers

I had a strange event occur with my watercooling rig. This might happen to other folks so I thought I should post. I have a lot of fluid in my system because I installed an automotive transmission radiator on my Quadcore about 2 years ago. Heres some fun pics:

Anyway, this dropped the temperature down to around 30C(to keep it cool during 10 hour 3DSMAX renders). Recently I've been fussing with it a lot and reconfiguring components and I decided to run pure water in it for a while to clean it out (I noticed sediment in the reservoir that I couldn't see in the green fluid) and see what happened. Then I forgot about it for a while with pure water in it. After a couple weeks a hose popped off the back of my machine, for the first time. PANIC! I refilled it and ran it on pure water again like a dope. A week later I noticed that the system had pressurized to the point that a pinhole stream of water was shooting out of the reservoir one morning.

I figure the one logical possiblity is that the water was contaminated (I use distilled water but its not air tight) and I must have been brewing some beer in my cooling system. The gas output from the bacteria/yeast/whatever was building up over time causing pressure.

I went back to a 50/50 with propelyne glycol/distilled water. I use Sierra automotive antifreeze which is supposed to be safer than ethylene glycol. The gas buildup has stopped.

Any insights on this phenomenon? I guess the chemicals do more than increase the cooling effect, they also disinfect the system and make it inhospitable for microorganisms.

Hope all is well.


Dec 12, 2007
everything is fine now the only other thing you could of done is clean out the parts with mild bleach but i wouldn't recommend doing that with pvc tubing as it can crack. but the antifreeze etc will stop bacteria growing now.
Shows how "pure" bottled water really is.
But yes, this is normal.
The anitfreeze has additives that extend the life of rubber hoses and seals, and rust inhibitors. In an automobile, the rust inhibitors are especially important. Running pure water can completely fill and clog a radiator with rust particles. There are also additives to combat electrolysis.

Where I work, we have an old UV Ink SPE drying system, which has a large radiator and water pump to circulate water around the UV light relfectors to cool them, the lights get hot enough to melt the aluminum relflectors. We hadn't used it for sometime, but we needed to restore the unit to service. Well, someone had filled the system with pure water, (held 20 gallons) and when I turned the pump on, the top of the metal radiator actually ballooned out, and started spraying streams of water out around all the seams at the top of the core. Took the radiator to a shop, and the thing was packed full of rust, no water what-so-ever could pass through it.
Had to have the radiator completely re-cored, and now it too is running a 50/50 mix, as it should have been all along.