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Since we intended to test how well mineral oil can dissipate heat compared to air or conventional liquid-cooling systems, we wanted to use some reasonably hot hardware to put the system to the test, and we had exactly that with the triple-slot Asus Radeon HD 7970 DirectCU II GPU. It's as hot as it is huge, measuring 2.25 inches thick and 11 inches long, but Puget's case had no trouble accommodating its length. This GPU gets so hot Asus had to stick a condo-size cooler on it, so we wondered if the oil would be able to handle all the heat this card gives off.
It should, because, in theory, even though the fans will spin more slowly since oil is more viscous than air, the lack of fan movement shouldn’t matter since the oil is sucking up the heat given off by the card, and the fans don’t play a major role in the cooling loop. Once the oil gets warm, it’s pulled out of the case by the pump and sent to the external radiator.
The only thing we didn’t like about the GPU setup is that it’s across from where the PSU is mounted, so we had to drape the cables through the acrylic case.
The Swiftech MCP35X pump included with this kit is not the standard unit that we used in this year’s Dream Machine. It's PWM-controlled, so it can adjust its speeds dynamically according to instructions given by the motherboard that it's plugged into. When the system is idle, the pump operates very quietly. When needed, it can crank up to 4,500rpm, so it's very powerful for its size (and you'll need that extra horsepower to offset the thickness of mineral oil). It also takes standard G1/4 fittings and can directly integrate specific reservoirs, which saves on space. At $100 when purchased separately, it's one of the more expensive pumps you'll find. But our oil-based setup benefits from a pump that has premium features.
Our oil came in one five-gallon jug and three one-gallon jugs. The big jug needed a pipe wrench to get the cap off, and it did not have a built-in tube like a gas can. So there was some spillage there. Mineral oil has the clarity and consistency of corn syrup. It also has no odor, thankfully. We began by emptying the large jug into the tank, which filled a little more than half its capacity. Then we inserted our rack of parts, and topped off the tank with one of the gallon jugs of oil. We ended up needing just six gallons since the rest of the container's capacity was displaced by the hardware and the pebbles. It got pretty heavy after everything was poured in, but there are silicone feet underneath the aquarium, so you can at least get your hands underneath to lift it.
The instruction manual recommends using bubble bars to simulate an aquarium, which requires a second set of pumps, valves, and tubing. We thought that was just a bit too complicated for our first time with mineral oil. But rocks and other typical fishy decorations are an easy add, as long as it's all clean. Any dust will cloud the oil and potentially clog the circulation system, or at least reduce its effectiveness.
The pump is just one part of the oil circulation system, of course. The Swiftech MCRx20-XP radiator uses brass tubes and copper fins, and a self-purging plenum, which is a chamber that helps maintain equal pressure throughout the loop and can suppress noise. The radiator is hung outside the case on a bracket. It's big enough to fit three fans if you wanted to; one up top and two down below. But the bracket is a bit too bulky to fit four fans, thus eliminating the possibility of a full “push-pull” configuration. The Scythe fans are 120mm units that spin at a fixed 1,850rpm, but they're surprisingly quiet and good at forcing air through a radiator. The fan cables aren't braided, so they're not very pretty. We also needed to add a power distribution block because the motherboard has just one case fan header, and we wanted to minimize the number of cables leading out of the case.
Trying something truly novel in Build It is exciting, but that excitement was tempered by several “oh, crap” moments and hardware failures. For example, it wasn't until all the hardware was dipped into the oil for the first time that we realized we probably should have made sure it at least booted first. Luck was not on our side, and on our first try the machine would not POST. We hoped the issue was related to the monitor, or the monitor cable, or some small thing, but no combination of parts outside the machine had any impact. We did have some luck, in that there was a plastic tub available in the Lab that was large enough to place the oil-soaked rack in temporarily. So we hauled it out and proceeded to methodically replace one part at a time until we got the machine to boot. The problem appeared to be a motherboard fried at some earlier point by static, or physically damaged in a way that's difficult to detect with the naked eye. Once we swapped the board, the system booted right up and remained stable.
The pump was initially a little noisy as it filled up and started circulating oil through the radiator, but the overall acoustics eventually settled down to a gentle whir, even when spinning at a reasonably high 4,500rpm. The loudest element was actually the oil pouring back into the case from the radiator, which was like a pleasantly babbling brook.
Overall temps seemed fine, so we ran FurMark's thermal test for a little while to get some heat into the oil, and the case temperature eventually leveled off at 37 degrees Celsius, comfortably below its rated maximum of 50 C. The Asus HD 7970 stayed around 60 C, though we did have to manually increase fan speed to compensate for the thickness of mineral oil. We found that temps are highly dependent on the fans you use on the radiator; random $5 case fans won't get the kind of result that you will get with $20 Gentle Typhoons (or Corsair SP120s, or Noctua CPU fans), because the higher-end units have a combination of high pressure, high durability, and relatively low noise. We didn't try overclocking the AMD chip, since it was using a stock cooler, and Puget warns against overclocking systems in the oil due to heat concerns.
The radiator fan wires were not long enough to reach the motherboard headers, so we used a power distribution block, which is like a power strip for case fans. You can power them up with Molex, SATA, or PCI Express power cables. The Gentle Typhoons we used spin at a constant RPM, but the noise is low enough that we don’t need variable speed PWM control.
Aside from human error, the system itself was a great success. People around the office who aren't even into computers stopped to admire our aquarium PC, with its bubbling liquid and eerie blue glow (provided by a 30cm BitFenix Alchemy Connect LED Strip). It’s obviously not for everyone, but if you’re looking for a fun DIY project that’s "different," it doesn’t get much better than this.