Old timer at work changed my mind on coolant mix ratios

I always ran 8% coolant concentration because that's what the manual said, but a 30 year guy named Ray pointed at the foaming in my sump and said 'that foam is making your tools dull, you're not cutting metal, you're cutting bubbles'. He showed me his logs from the last 6 months on the same VMC and his insert life nearly doubled at 5%. Since then I dropped mine down and the finish on 4140 is way cleaner, anyone else trust the seasoned guys over the book specs?

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the_angela1mo ago

Tbh, foam around the sump is pretty normal on a lot of machines, and 8% vs 5% might just be splitting hairs on a good day. Those 30 year guys mean well, but they also tend to blame the coolant before the speeds and feeds.

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