I'd use it to help someone who wanted a non-detergent motor oil. There was an older gent who had an unrestored Hupmobile. I asked the tech folks what to recommend. They said the hydraulic oil sold at the time was what he wanted. It had anti rust, wear and foam additives. It was only sold in ISO grades, so if they wanted SAE 30, using the chart, they got ISO 100. Believe it or not, after getting past the idea of using hydraulic oil for engine oil, the biggest roadblock to them buying it was the smallest container was a 5 gallon pail that cost about $10 in 1985.