TIL that old school coolant mix advice from a guy in Dayton was actually right

I always thought the 7% concentration rule for synthetic coolant was just shop lore, so I ran mine at 5% for years to save money. Last month I had a rash of rust issues on some 4140 steel parts after a weekend. Tried his exact mix and the parts came out clean after sitting for three days. Anyone else have a specific coolant ratio that works for tricky materials?

2 comments

2 Comments

angela_park1mo ago

Interesting. What was the exact ratio he gave you for that 4140 steel? I've had mixed results with the generic advice and material-specific mixes seem to be the real key.

jason_fisher41mo ago

Ugh, tell me about it, @angela_park. He said 1 part cutting oil to 5 parts kerosene. Works way better than the all-purpose stuff they sell.