Physical and electrical design

The Thermaltake BigWater 760i is comprised of two distinct units: A water pump/reservoir/fan, and a CPU heatsink block. The former is contained in a single assembly and fits into two consecutive 5.25" drive bays. The coolant reservoir and pump are toward the inside of the computer while the 120mm fan is mounted above a finned radiator. Water is pumped out of the reservoir, into a clear plastic tube, into the CPU water block, through the other side of the block and out another tube, then into the radiator to cool down, and back into the reservoir.

The CPU block is solid copper, and requires special mounting apparatus. All of the necessary materials are included with the BigWater package, but substantial system disassembly is required -- you have to remove the motherboard entirely, then carefully assemble the mounting materials, then put the block on, then remount the motherboard.

Aside from the CPU mounting assembly, the rest of the system is not difficult to put together. The most you have to do is measure and cut some hoses, and affix some connectors to each end. Despite the simplicity of this explanation, it actually takes about 4 hours to assemble and install the BigWater 760i, including sufficient test time.

The 120mm fan is adjustable internally through a potentiometer, from dead-quiet speed to barely-audible speed. The fan also has a blue LED inside, which flickers a bit as the fan spins; the light is visible through the perforated front grating of the BigWater drive bay unit.

Putting it to the test

As I mentioned above, the assembly is rather grueling. Fortunately the instructions are easy to follow, and include a variety of CPU configurations.

With any liquid cooling unit, you want to test it outside of the case before you complete the installation. This ensures that there are no leaks or malfunctions that could harm the electrical parts of your PC. At first I had trouble getting the pump to work -- it wouldn't switch on. The problem was air in the line, which was easily solved with some creative maneuvering. Also, make sure that you don't cross the in and out tubes to the CPU block. Since there are check valves preventing negative flow, the pump won't switch on if they're not connected to the right tubes. Anyway, once the air was out of the line, the pump began working and everything seemed to be in order.

I continued my testing by allowing the pump to run for about 30 minutes, all the while testing the tube connections to make sure that there were no leaks that would only show up through stress or time. Satisfied that everything was properly assembled and working as intended, I installed the BigWater 760i in an Antec P182 chassis and turned the system on. I was amazed by how quietly everything worked -- the old Coolermaster CPU fan I'd been using was unusually loud, and I didn't notice it until it was gone.

Click for directory of BigWater 760i installation photos

I obsessively checked for leaks, made sure the reservoir was filled, eliminated air bubbles in the line, and checked the CPU temperature to make sure the cooling unit was doing its job. Everything was fantastic. I even overclocked the processor a bit using the built-in automatic functions in the Asus P5B motherboard, and eventually hit the limits of my RAM without heat-stressing the processor at all. (Unfortunately I forgot to record the air-cooled ambient and load CPU temperatures, so I don't have numbers to compare to the BigWater 760i. Take my word for it -- it's significantly lower in temperature with the liquid cooling solution.) Overall I was really happy with the BigWater 760i. I clocked the CPU down a little bit past the limit I was testing to, and checked for leaks every day for about a week.

I put off doing this review for several weeks due to other commitments. I also wanted to see how the hardware held up over that time; experience in electronics says that most failures will happen within the first 30 to 90 days of regular operation. As it turns out, such a failure did happen -- but not right away. Some two or three weeks after the installation and testing, the fitting that connects the output hose to the pump developed a leak. This is not one of the parts that is user-assembled -- it comes out of the box pre-attached -- so there's no way that I could have caused the error through faulty assembly. This was definitely a factory defect.

Fortunately, anti-freeze is self-sealing, so the leak did not last for very long, and it did not completely drain the reservoir. But enough fluid leaked out into the wrong places to damage my power supply and motherboard. Anti-freeze is one of the most corrosive substances that ordinary consumers will come into regular contact with. It corroded the IDE connector, the power supply connector, various board components, and ate the metallic finish off of the inside of the P182 chassis. In all, it was quite a disaster, but nowhere near as bad as it could have been. I didn't notice the problem for at least a week because the system was still functioning up until the power supply failed. At that time I opened the machine and found dried coolant and corrosion in several places.

Even though the unit is pretty tightly sealed, you still need to refill the coolant reservoir every few months. Whereas with air-cooled solutions the most maintenance you'll ever have to do is blow out the heatsink with compressed air, the maintenance for a liquid cooling system is a bit more involved and expensive.

The BigWater 760i comes with enough coolant to fill the reservoir once and maintain a reasonable liquid level for about a year. After that, you can buy more coolant from Thermaltake. Could you use regular automotive anti-freeze? I'm not really sure. However, I do know that all coolants are not chemically compatible or functionally identical, and that the Thermaltake solution includes an ultraviolet-sensitive compound that reacts to blacklight, so my advice is to use only approved coolant in this unit. It's about $18 per 500cc bottle, which should keep you going for another two years or so after your first included bottle is finished.

Conclusions and manufacturer recommendations

Despite the factory defect that caused about $175 in damage to my machine, I actually think that this is a pretty decent liquid cooling device. If you get one without the leaky fitting (or if you take precautions against leaks somehow), you'll find the Thermaltake BigWater 760i to be affordable and effective. Realistically the failure I experienced is possible with all manner of liquid cooling apparatus, and it was not a permanent failure. In general, liquid cooling in an electrically sensitive machine is an inherently risky proposition that requires a great deal of attention and long-term maintenance. However, it's the only way serious performance enthusiasts can push the limits of their CPUs, so it's a risk that comes with reward for overclockers.

I like the overall BigWater 760i package. I just wish it hadn't leaked on me. Moreover, I wish it hadn't leaked after I had tested it and was confident that it was properly sealed and production-ready. That aside (and perhaps a request for more thorough product QA testing) I can't think of any specific recommendations for Thermaltake with regard to how the product can improve in the future.