A good easy to read & understand mini tutorial on the relationship between an oils Flash Point & NOACK % Evaporation https://www.machinerylubrication.com...ty-flash-point & how they can indicate how our engine oils VOA measurements of those two items, can indicate how much oil consumption we might expect from evaporation of our choice of engine oil lubricant. Both are different tests, performed at different temperatures, but give us an idea of how good our lubricant base oils are & allow us to choose engine lubricants that won't "evaporate"/be consumed & require top-off during a OCI. Of interest toward the end of the article = "On the other hand, mineral oils may start to vaporize much earlier than their flash points". I apparently had this happen to me back in 2011 when SN/GF-5 Havoline 5W-30 went in the family fleet & three of the vehicles that had never consumed during an oci, suddenly began to consume after 6 to 8 week time frame, as the lubes base oils began to break down. Havoline NOACK suddenly went UP to over 15% on their SN/GF-5 recipe, so something not so good happened between SM/GF-4 & SN/GF-5 on Havoline. Many other SN/GF-5 engine oil recipes NOACK also went up, so if any of your family fleet suddenly began to consume when your first use of SN/GF-5 lube went in, suspect their base oil quality changed & their Flash Point &/or NOACK % Evaporation may also have gone up with the SN/GF-5 recipe.