About PC fans sleeve bearings and pure mineral oil.

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Hi, I have some very old computer fans (8x8 and 9x9cm) whose sleeve bearings are a little worn (but not much, they still work without shaking too much). I have been oiling them for a few years with SAE 20W-50 motor oil and it works fine for me for a long time (and not so much with 3 in 1 because they last less than motor oils. Probably evaporate quickly due to their low viscosity. I suppose the same would happen with sewing machine oil because it is very light, although I have not tried it).

My question is (mainly curious) if pure mineral oil (some also call it liquid paraffin, usually sold in pharmacies and used on the skin to moisturize it) are also good for lubricating very small bushings such as those in pc fans.

This pure oil caught my attention because it is highly refined and virgin (it can be safely used on human skin and other cosmetic uses), is non-detergent and apparently it is completely dielectric (I have heard of motherboards immersed in this oil and working at the same time), but I guess it doesn't have something that, in my opinion, is very important: the anti-wear additive to reduce metal-to-metal friction as much as possible, and I'm not sure if this can withstand the high temperatures that a sleeve bearing reaches.

What do you think about this type of oil? Is anti-wear additive really necessary for these very small sleeve bearings? I have heard that pure mineral oil is recommended for sewing machines and razors/clippers because it is clean, has no detergent additives and does not get sticky, but what about the lack of anti-wear additive? The goal is to prevent bearing wear as much as possible with a lubricant that forms a strong and durable film. At the moment, motor oil is the most reliable thing I know. Thanks.
 
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I have been refurbishing old sleeve bearing PC fans for decades. What I found that works the best (without going to extremes in cost or effort, considering an old fan is worth about $1 unless a proprietary design), is a mix of low viscosity motor oil, like 0W-20 or 5W-20, mixed with lithium grease to a viscosity where the drop point is barely above room temperature.

This gives you the thicker film strength to combat the wear, so the shaft doesn't move in an elliptical direction as much (is how the bearings typically wear, not just evenly larger diameter all around), doesn't pump out as much, but with the thinner base oil, the sintered bronze bushing can soak it up better through capillary action, to resupply as the oil slowly dries out or pumps out.

I also put extra lube in the bung area, and make sure the rubber bung seal, seals completely or else I put a sticker over it to help the seal... if the original seal is still sticky enough, will use that, but usually it is degraded and a new sticker is needed. I use clear laser printer envelope labels. They're some kind of thin film plastic not paper, though a plastic laminated paper label is still better than nothing, or even electrical tape.

Sleeve bearings in PC fans don't usually get very hot except in certain uses like tiny video card heatsinks where the fan is butted up against the 'sink, unless it's a very powerful fan, spinning at high RPM to get there and even then, it's nowhere near the temp limit of mineral oil or any other petroleum based lube.

Dielectric doesn't matter, conduction of anything reasonable to use is near enough if not completely dielectric.

It's not an anti-wear additive that matters as much as what I mentioned above, a low enough viscosity base oil for the bushing to soak up a reserve, along with grease to form the film that takes up play, and trying to seal the bung hole so more reserve can be stored there, and depending on how much the fan has worn, relubricating it again every few years, or roughly after +/- 5K hours at least checking it... depends on how badly it was worn, the RPM, and other factors.

If I had to only use one single thing to relube a fan instead of an oil-grease mix, it would be 80wt gear oil unless you are relubing them before they have any significant wear which is the ideal, but is seldom the situation. "work without shaking too much" seems like enough wear that only using a very low viscosity oil isn't going to cut it. I mean that can work too, but the wear will increase faster and it will have to be relubed more and more often, the more it wears.

Lastly, worn sleeve bearing fans are poor candidates to use in a non-vertical orientation. I'd sooner just get a new, dual ball bearing fan for such an application.
 

CleanSump

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TW2000 gun oil in mine. I've also used jojoba oil, but it's a tad thick. But the gun TW2000 seams to work well.
Trans fluid would be my next choice.
 
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It’s been a while since I had to lube a sleeve bearing fan, but I’ve always added a drop of 3-in-1 oil or Tri-Flow to it. That Zoom Spout oiler, which Oatey/Hercules sells is a pure oil, no citronella like 3-in-1 or Teflon and 2-butoxyethanol like Tri-Flow.
 

Electrode

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I have been refurbishing old sleeve bearing PC fans for decades. What I found that works the best (without going to extremes in cost or effort, considering an old fan is worth about $1 unless a proprietary design), is a mix of low viscosity motor oil, like 0W-20 or 5W-20, mixed with lithium grease to a viscosity where the drop point is barely above room temperature.

This gives you the thicker film strength to combat the wear, so the shaft doesn't move in an elliptical direction as much (is how the bearings typically wear, not just evenly larger diameter all around), doesn't pump out as much, but with the thinner base oil, the sintered bronze bushing can soak it up better through capillary action, to resupply as the oil slowly dries out or pumps out.

I also put extra lube in the bung area, and make sure the rubber bung seal, seals completely or else I put a sticker over it to help the seal... if the original seal is still sticky enough, will use that, but usually it is degraded and a new sticker is needed. I use clear laser printer envelope labels. They're some kind of thin film plastic not paper, though a plastic laminated paper label is still better than nothing, or even electrical tape.

Sleeve bearings in PC fans don't usually get very hot except in certain uses like tiny video card heatsinks where the fan is butted up against the 'sink, unless it's a very powerful fan, spinning at high RPM to get there and even then, it's nowhere near the temp limit of mineral oil or any other petroleum based lube.

Dielectric doesn't matter, conduction of anything reasonable to use is near enough if not completely dielectric.

It's not an anti-wear additive that matters as much as what I mentioned above, a low enough viscosity base oil for the bushing to soak up a reserve, along with grease to form the film that takes up play, and trying to seal the bung hole so more reserve can be stored there, and depending on how much the fan has worn, relubricating it again every few years, or roughly after +/- 5K hours at least checking it... depends on how badly it was worn, the RPM, and other factors.

If I had to only use one single thing to relube a fan instead of an oil-grease mix, it would be 80wt gear oil unless you are relubing them before they have any significant wear which is the ideal, but is seldom the situation. "work without shaking too much" seems like enough wear that only using a very low viscosity oil isn't going to cut it. I mean that can work too, but the wear will increase faster and it will have to be relubed more and more often, the more it wears.

Lastly, worn sleeve bearing fans are poor candidates to use in a non-vertical orientation. I'd sooner just get a new, dual ball bearing fan for such an application.
Those gear oils are quite expensive in my country (they cost a lot more than a new fan, so it's not worth it), so I decided to make a mixture similar to the one you mention but with what I already have at home: 3 in 1 or sewing machine oil (low viscosity oil) and bearing grease. I have a fairly thick grease (because it is for industrial bearings), but the idea is to just mix a very small "chunk" into the oil to increase the viscosity, enough that it forms a good film and stays firm on the bearing sides. What do you think?
 
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^ Yes that will work, you want it barely thick enough that it doesn't drip off a toothpick. If starting with very thick grease, it's going to take a while to mix it up with the oil, and since a fan only needs a few drops at most, I just mix up a batch in a plastic bottle and have it ready for the next time I need it. I mixed a few ounces by putting a little wisk in a drill press and letting that run a couple minutes.

As far as the expense of gear oil, I already have some, but then anyone servicing their own vehicles is going to have grease and lower viscosity oil too.
 
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