I am surprised his clients let him experiment on their cars. I have been using Havoline 20w-50 in my Cultus Carby 07 since I bought it in 2010. At that time it was 30k driven and now it is about 100k driven. I change it at 3k mileage and no drop in oil level observed till now. Car is CNG and more than 60k mileage has been on gas. Personally I believe its just a way for oil shop guys to sell the product that is not selling well.
P.S. I use Shell Helix 5w-30 in Corolla 07, 91k driven and change it at 4k mileage. No drop in oil level ever seen.
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