Spindle Coolant Disappearing

Hi guys,

I’ve got an HY spindle with a custom water cooling system.

Everything works great with one exception. The coolant reservoir is getting lower, and there are zero visible leaks. No drips, moisture, or even evidence of past dripping anywhere.

Could my spindle be consuming coolant somehow? Perhaps a bad seal or something?

Thanks for any advice!

I have run a HY for coming up to 3 years and in all that time have only added around 1 pint of top up to the reservoir.
My system is home made with a 25L / 5 G plastic box with a clip on lid.
The coolant pump is submerged in the tank there are 2 small hole in the top 1 for the flow pipe and one for the return which discharges just below the coolant level
The tank is on the floor under a bench and has around 20ft of flow & 20ft of return clear pipe with a flow indicator mounted near to the 10" touch screen
The system is filled with around 70% high quality automotive anti freeze and 30% deionised water.
My average workshop temp in UK is prob around 20 degrees C the spindle ran for 8 hours yesterday at 19000 rpm profile cutting British Oak with a 1/8 up cut bit full cutter width 3.5mm step down at 120 inches per min and the body of the spindle barely rose above the temp of any other metal in the shop.
The coolant channels in the spindle are fairly basic and most pumps operate at a fairly low pressure but with reasonable flow rate
How much does it appear to be loosing?
What’s your ambient temp? could it be evaporation?
I cant imagine a leak that you wouldn’t see
I would run the pump but not the spindle place some tissue paper under the collet and let the pump run for an hour or so if no indication the do the same test with the spindle running make sure you have acutter in and tightened or if not remove the collet and nut.
Hold a tissue against each pipe joint to check.
The last option is to by an addative that you would add to the system and run which shows up under uv light
Hope this helps let us know how you go


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It shouldn’t be evaporation since the system is fully sealed. The reservoir is a small PC based reservoir so it holds very little by comparison to your system. It relies on a radiator for heat distribution/cooling.

At first, I attributed the lowering level in the reservoir to colder temperatures in my shop, but no matter what the temperatures are, the trend is only downward. Not to mention, when the coolant warms up from use, there is no visible difference in the reservoir level, so that can’t be the issue.

I’ll try your suggestions and see what I find.

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Hey chargedmr2,

you have a little gnome in your system that lives of drinking ethylene glycol.

:joy: It sure feels that way!!

Well, this may have been a much simpler issue than I thought!

I discovered that there were quite the number of air bubbles trapped in the radiator. After a bunch of tapping on the radiator with the pump running, they seem to have all come out. And the coolant in the small reservoir dropped a bit more. I had figured that any air in the system had been long gone, but obviously I was wrong about that.