Why coolant goes rancid, and how to make it last longer
That Monday-morning smell from the sump is bacteria sending you a signal. What causes coolant to go rancid, and the key points for extending its life.
Bacteria cause the smell
Water-miscible coolant is mostly water, which makes it an easy place for bacteria to grow. When anaerobic bacteria, which thrive without oxygen, take hold, you get a rotten-egg smell and the emulsion may split or change color. That is why the smell is worst after a weekend or holiday shutdown.
Five things that speed up spoilage
The more of these conditions overlap, the faster coolant goes bad.
- Tramp oil: way oil and hydraulic oil form a layer on the surface that cuts off oxygen.
- Chips and sludge: deposits at the bottom of the sump become a breeding ground for bacteria.
- Stagnation: when circulation stops, oxygen runs short.
- Low concentration: biocidal performance drops.
- High temperature: bacteria multiply faster.
Key points for longer coolant life
Tackle the causes one by one and you can stretch the time between coolant changes.
- Skim off floating tramp oil regularly.
- Remove chips and sludge on a schedule.
- Keep the coolant circulating even on days the machines are idle.
- Hold concentration within the recommended range.
- Keep temperatures from climbing in summer.
Taking the manual work out of it
Doing all of this by hand every day is hard to sustain. Equipment that keeps sump coolant circulating, filters out solids and tramp oil, and holds concentration and temperature lets you deal with the fluid before it turns.