Oil-Immersed Raspberry Pi Keeps Its Cool Under Heavy Loads

As a general rule, liquids and electronics don’t mix. One liquid bucks that trend, though, and can contribute greatly to the longevity of certain circuits: oil. Dielectric oil cools and insulates everything from the big mains transformers on the pole to switchgear in the substation. But what about oil for smaller circuits?

[Lord_of_Bone] was curious to see if an oil-cooled Raspberry Pi is possible, and the short answer is: for the most part, yes. The experimental setup seen in the video below is somewhat crude — just a Pi running Quake 3 for an hour to really run up the CPU temperature, which is monitored remotely. With or without heatsinks mounted, in free air the Pi ranges from about 50°C at idle to almost 70°C under load, which is pretty darn hot. Dunking the Pi in a bath of plain vegetable oil, which he admits was a poor choice, changes those numbers dramatically: 37°C at idle and an only warmish 48°C after an hour of gaming. He also tested the Pi post-cleaning, which is where he hit a minor hiccup. The clean machine started fine but suffered from a series of reboots shortly thereafter. Twelve hours later the Pi was fine, though, so he figures a few stray drops of water that hadn’t yet evaporated were to blame.

Is oil immersion a practical way to cool a Pi? Probably not. It doesn’t mean people haven’t tried it before, of course, but we applaud the effort and the careful experimentation.

[via r/raspberry_pi]

56 thoughts on “Oil-Immersed Raspberry Pi Keeps Its Cool Under Heavy Loads

        1. Intel were running long term tests on this for server usage. Zero effect after two years of immersion was the end result I seem to remember. I can’t find that test from a quick google but I found these folk who have been in business since 2009 and presumably wouldn’t be if mineral oil wrecked servers ;) https://www.grcooling.com/

          I did the mineral oil immersion thing for a while. There are some tricks to it like get food grade mineral oil since it doesn’t smell much unlike car-grade mineral oil. Second tip is seal up your connections somehow since this stuff will wick up any cable you put in it. Third tip is that you really need to drain the oil out of any connectors if you’re doing things like swapping PCI-E cards since it’ll block the contacts from making connection. Oh, and remove any stickers before your machine goes in oil since the adhesive will fail and cause stickers to float around in the container.

      1. Distribution transformers are filled with oil. I thought it was mineral oil but a quick google shows it was just a mineral oil based formulation. I would still think mineral oil would be more than adequate for this particular application.

    1. Yup Mineral oil is perfectly cromulent, see the linked article in the last paragraph. I just had a Corsair H60 finally die on me after 7 years of operation, been thinking about something to do with the radiator. A mineral oil immersion cooled Pi (or x86 jobby) circulating thru an external radiator may be fun and ridiculous overkill.

  1. What will be the effect of the change in electrical permittivity on the PCB traces running at GHz, most of which were calculated assuming air.

    Relative permeability of air 1.0006
    Relative permittivity (dielectric constant) mineral transformer oil (2.4 to 4.0 from 25-90 ºC)
    Relative permeability of distilled water 80.0

    I’m naturally going to assume mineral oil here (because using vegetable oil is just such a bad long term idea).

    1. After reading your question, I did an FTDT simulation of a simple microstrip line on FR4 with an air-box of Er=1.0 vs Er=4.0 (to simulate the oil). There was no significant difference in S11/S21 ( -20 vs -15 dB return loss respectively).

      1. I’d expect there to end up being convective pools of liquid around the hot parts, refreshed by newly liquified grease flowing in, and maybe some liquid grease moving away and downwards before cooling again. Grease on cooler parts would remain more viscous.

        Might not be as effective as a fully liquid bath but might avoid some of the drawbacks of liquid.

        1. On further research I’m not finding any greases that would behave like this (melting to liquid) at a useful temperature. You’d probably need a specially made formula with a low dropping point. So nevermind.

  2. 70 degrees Celsius is not dangerously hot for most processors. The thermal limit for the chip on a Pi is 85 degrees, so this isn’t even reaching a point where thermal throttling is an issue. People seem to like to anthropomorphize computers and imagine them being uncomfortable at temperatures we wouldn’t find bearable. That’s silly. Listen to the engineers.

    People are going to start claiming that chip life is adversely effected by running at the upper range of the chip’s rated temperature. I’ve heard the just-so stories and anecdotes before, but I haven’t seen real, experimental, replicated evidence of that yet. If you have evidence, please make it known. A lot of gaming cooling rigs are ridiculously over-engineered–like 600-2000% of what you’d ever need. It’s pure marketing, no science, and people fall for it because they’re paranoid.

    You’re going to regret a mineral oil bath when it’s time to change out some connectors. Ask me how I know.

    1. Yea but there is the 10 degree rule: “Every 10°C increase in temperature reduces the life of electronics by half”. So running hot will work just fine, but there is a trade off, you just need to replace it more often.

      1. I understand that a 10C increase doubles the rate of chemical reactions, but I don’t know how that maps to component lifetimes. Who cares if millenia of expected operation gets reduced to mere centuries? References, please?

        1. Plug “10 degree rule electronics” into your research search engine of choice, and read the references you will find. But ultimately you are right, it is the Arrhenius equation.

          “millenia of expected operation” ?????? What electronics item are you talking about that has functioned for a millenia ? If I was cynical I would say that is partially the reason why most products with no moving parts have an engineered failure just outside their warranty period.

          The failure curves fits the observed data collected over the last century by many manufacturing companies, run a product in a desert and the failure rate is very high, run the same product in Antarctica and the failure rate is extremely low. It is not magic.

          1. I should probably add that it is how reputable companies in IC manufacturing burn out the early failures, they put the chips in a high temperature oven and power them up and run test programs that will use maximum power to weed out the early failures the chips that would have failed within the first 7 years of operation. Tghen after 8 to 24 hours they move the chips onto the nest stage of QC. It is part of the reason why people without access to industrial manufacturing knowledge think that IC’s NEVER fail.

          2. Regarding the question: “What electronics item are you talking about that has functioned for a millenia?”
            I would like to reply a “leiden jar”, now as I’m aware of there aren’t any of these who are actually a close to being that old… but the ones that are present at this time and day… in musea… could be operating for that long. And I doubt if the 10 degree rule would apply to that particular component. But that doens’t compare to modern electronics which is made to last a year maybe five and for a cost that requires shortcuts in the design. Yep modern electrnics is build to fail. So every effort that could be taken to prolong it’s lifespan could make sense. That doesn’t mean you should pay hundreds of dollars for a water cooling system because every components added to the system is just another point of possible failure.
            Dunking it an a bath of oil making it impossible to do proper maintenance is ridiculous for consumer electronics. Perhaps even reducing it’s lifespan because certain components will absorb the oil and causing unwanted expansion and stress as heat still build up, think about the oil penetrating into the chip slowly… (it will happen just give it time could be years). You may wave this away stating that that effect could be neglected as too small. But think about the fact that the circuitry inside the chip is very very tiny and does not need much. So when you heat it and it will expand we all know the article about “wax-motors” from few weeks ago here on hackaday. Do you want that in your precious chip you are trying to preserve? Commercial electronics isn’t made for this so you should not be doing it. it is fun for a sunday afternoon. But even then… use the correct oil unless you are prepared to throw it away anyhow.

            Heat is a problem simply by the fact that it brings the item closer to the point it will eventually fails at no need to argue about that. Thermal cycles are killing, materials expanding and contracting, higher temperatures or allowing heat to build up is simply a problem visible with common sense, no statistics required.

            Regarding failure rates being lower in Antarctica then in the desert… interesting, though I always need to have some more info about how these statistics were acquired. What was the range of product used? And how often was it use and under what circumstances, because some appliances simply die by having certain people only “looking” at it (that is what they said they gave it to me to repair it). Also what would work better/harder/less and under what circumstance, a refrigerator or an electric heater? And how would that affect your statistic?

          3. And I would reply to a “leiden jar” only if the metal used were 100% pure gold, or was stored, and operated, inside a vacuum. And then you have shifted the problem to maintaining a vacuum to a thousand years (space maybe?) or preventing someone from stealing your gold, from beyond the grave. Oxidation rates of any other metals in our atmosphere would exactly follow the Arrhenius equation every additional 10 degrees double the oxidation rate. I do agree with “thermal cycles killing”, if it can break mountains into dust ( https://en.wikipedia.org/wiki/Weathering#Thermal_stress ) what hope do chunks of silicon have.

          4. Okay, oxidation of the metal inside the leiden jar could indeed be a problem. An gold does indeed solve that (sealing the whole thing filling it with an inert gas (helium) or keeping it vacuum (just like a vacuum tube / radio valve) could be a problem over long time.
            But the fact that gold could be stolen might be completely true… BUT it isn’t fair… as it has nothing to do with building something that could TECHNICALLY last forever (correction millennia).
            Anyway, thanks for pointing out the Arrhenius equation, didn’t look at it from that perspective.

          5. I do agree with an inert gas, but I would not have picked Helium (or Neon) since it is lighter than air. I would have picked a heavier one, possibly Krypton over Argon in terms of slightly less (0.037%) radioactive isotopes. Oh, and one of the minor industrial uses of helium is to detect leaks since, due to its small size, it diffuses three times faster than air through solids. I’m not saying that the rate of leakage by diffusion of helium could not be reduced as a problem with good engineering, why bother, just avoid that problem with a simpler choice.

    2. It’s electrolytic caps that tend to lose their life with temperature increases. It’s why the big motherboard and GPU manufacturers have moved towards long-life electrolytics.

      Offhand, I don’t believe any version of the Pi has electrolytics on board, so no big deal.

    3. It’s fking overkill. Who cares if the life of the PIs CPU is reduced by a few years, it’s a damn $35 SBC buy a newer much faster one if a few years if you actually manage to kill it

  3. Meaningless nonsense.

    ” 37°C at idle and an only warmish 48°C after an hour of gaming” You’re warming up the entire volume of oil. Was the 37 or 48 terminal temperatures or was the oil temperature still rising after “an hour of gaming”. Why one hour? Increasing the volume of oil will increase the thermal mass meaning it will take longer to reach terminal temperature, and also alter the rate of dissipation (lower temperature dissipates heat slower, but larger volume may also mean larger area of heat exchange with the environment).

  4. Once the oil gets to max temp, the chip can no longer radiate any more heat and will fail. Same problem with water cooled systems, you still have to remove the heat from the coolant liquid, using fans, peltiers, or such.

    The only benefit I see here is the Pi chip only has about 1 sq inch of surface area, where the oil has ~40 sq.in. in that setup.

    I have thought about using a car radiator w/fan mounted outside my office with coolant hoses running through the wall/window. That would help remove the heat from my office as well, no sense removing the heat from a CPU and then expect the AC to then remove the heat again.

  5. Isn’t the ideal cooling fluid one that boils at the temperature that you wish to not go above? So oil is worse than water, in just that regard. Also vegetable oils often contain phenolic acids, which obviously have corrosion potential.

        1. I built an early reflow soldering device with boiling fluoinert. Used reflux and you lose very little (a good thing as it wasn’t cheap). I’m not sure if you can get the stuff now, as it’s essentially a type of freon (fluronated hydrocarbon) but back then you could get various types with different boiling points…and it’d work great for this.
          Here are some current examples, though these temps are a little high for this:

  6. The subsea oil & gas industry uses electronics in oil in some applications. The oil allows for heat dissipation but primarily allows subsea pressures directly onto the circuit boards. This way you don’t have to put the electronics into a 1 atm pressure vessel when you take them subsea.

    Qualification work to prove that the electronics will last requires testing under pressure and temperature in oil for extended durations. High test temperatures are typically used to simulate lifetime aging. (https://en.m.wikipedia.org/wiki/Arrhenius_equation)

    Here is an example of a company that uses electronics in oil for subsea applications: http://www.zetechtics.com

    1. I once saw a TO-3 transistor that had been used in the depths of an oil well.
      Its pressure vessel had failed and the dome of the transistor was squashed flat against the silicon die.

  7. Mineral.oil.is an interesting.compound. We use it for breadboards and, mixed with eater at.2.5-5 TBLsp.per gallon, use it for summer or winter dormant tree spraying. Yes, this oil mixes with water. This could be a plus… like alcohol removing water from a gas tank… warm oil would bring humidity out of a ckt to where it would evaporate.

  8. We use DI water to cool high voltage electronics all day long, north of 100kV in some instances. pretty industry standard stuff, actually. The key is keeping the DI water – DI water by using a closed loop system and some bypass flow through de-ox and de-I beds. For this low of voltage I wouldn’t even worry about the exposed metal. A dip in conformal coating would take care of everything but the connectors, which again would be no big deal, gold plating would help too. The water would likely eat the pi eventually (wouldn’t we all) due to it wanting to pick up ions wherever it can, but I bet someone could get a year or two out of it. And as for electrolysis, it doesn’t work so well in DI water… which is kind of the point.

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