That is a good post and the link is an excellent article, Thank you for posting it. I read all 10 Chapters (did not take the test). I do not disagree with anything that Dr. Haas wrote
I did not read anything in Dr. Haas article that disagreed with my notes either. In Chapter 6 he recommends if you buy oil on the road and have to make a change due to availability then you should go to a lesser "weight" but maintain the same brand. He did not go into detail on proprietary additives.
The intention of my point was to say that each brand of oil contains a specific recipe of additives that are designed to work together. The combination, and ratio's of additives and how they work together is very relevant.
When you mix different oils you are making your own custom blend of additives that may or may not work well together. Oil manufactures have open license to develop their own recipe based on certain combinations of additives and how they respond in different environments.
My understanding, flawed or not is based on my experience selling gearboxes. The company I work for has spent more money than I will ever make testing oils to be sure of compatibility in the environments that we put our equipment in. These tests are expensive and time consuming. We have very specific recommendations for each unit installed. We will absolutely void the warranty if the oil recommendation is not followed. And we can tell. When customer X calls up and asks if he can use brand Y we may or may not have tested it. If not we will probably not test it unless a lot of customers want that brand of oil. Oil companies will not tell us what their additives are, if they did we would not have to spend so much of our profits to evaluate the oils.
Do all of my customers run the oil we tell them to? Nope. When they do not run the recommended oil it is usually because they have a lot of other equipment that uses a different oil and they want to standardize on one oil in the facility. Do they run for years? Yup, But they also do lots of PM, change the oil multi-seasonally and have routine oil tests performed (by us or independent labs) to look to see what kind of metals are breaking down in the oil. If they see 52100 we know a bearing is wearing, aluminum bronze, then bushing or gear shims are wearing etc. I can pull two ounces of oil out of a reducer that is in service, and send it in to the lab, most of the time if I include the serial number of the box, the lab in conjunction with Engineering can tell the customer exactly which component need to be replaced and we can send that component into the customer so on their next shutdown the can go in and do a preemptive repair.
We absolutely always tell all customers that if they are going to change their oil brand then they must drain the old oil out completely. I think you will find that practice to be an industry standard.
My gearboxes run in far more controlled and engineered environments than my motorcycle does, so IMHO (which ain't worth more than a quarter and that wont even buy you a cup of coffee 'cept at my house and you are welcome to that anytime
) the ounce of caution in the industrial world is worth a ton of prevention in my personal world where my pocketbook takes care of catastrophic issues.
The most expensive oil change is far less than the least expensive motor job. Why mix when the product is available everywhere darn cheap per mile traveled you can always run one brand out at oil change and then switch? There is a lot of science, technology and effort behind recomendations made by a company when they recomend a specific oil, Messing wih it is just out of my comfort zone.