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Glycol type for spindle chiller?


May 15, 2008
Winona, MN, USA
Hi Guys,

I have a 8HP liquid cooled spindle in a early 2000's vintage German CNC router. I bought the machine inoperative and I am getting it back online after a 8 year nap. The manuals say to use 20% glycol. But despite mentioning 20% glycol multiple times, it never says ethylene or propylene.

There is a little bit of green in the chiller tank. So my guess is that the proverbial last guy was running automotive coolant. The system is closed loop and it has a covered tank in the cooler. It is not pressurized beyond the pressure from the 1/2 HP circulation pump.

Should I just do 1 part automotive coolant concentrate to 4 parts de-ionized water and call it a day?


Ethylene seems to be more chemically reactive and is poisonous, so unless the system is marginal from a BTU standpoint, polypropylene is a better choice.

Thanks. I had read those. The ethylene glycol toxicity doesn't really concern me. I have so much heavy equipment and vehicles with antifreeze in them. The only times I have used propylene glycol is in hot water heating applications where the water is run through a heat exchanger with potable water.

Corrosion. Lubrication. And we don't know the thermal characteristics of the compressor heat exchanger, it might go below freezing in part of its cycle.

The corrosion and lubrication make me thing an automotive antifreeze is probably closer to the right stuff than a commonly available propylene glycol antifreeze which is is commonly used in boiler / hydronic heating applications.

So yeah, just going to go with automotive antifreeze.

-It's worth noting that a good many cars today use the propylene, so it, too, is undoubtedly an "automotive" coolant. (Pedantic, I know. :D )

Personally, I'd use propylene, if for no other reason than any cleanup and disposal issues, if there's ever a spill or you need to change it for some reason.

But either one will work for you. If they're only asking for 25%, the 'coolant' is only in there for its lubrication and/or anti-corrosion properties. The spindle itself will never know the difference.