Quote:
Originally Posted by 40 Deluxe
During my 27+ years as a mechanic for Arizona Hiway Dept. we saw the opposite. We ran 15W-40 diesel oil in everything for many years to reduce inventory. When we were thinking of extending oil changes from 5,000 miles to 7,500 miles in cars and pickups, we did a lot of oil sampling. The oil in 350 Chevy pickups would often start to thicken after 5,000 miles if used hard. Seems like some samples came back as 50W!
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Interesting..my experience with viscosity modifiers comes with higher soot numbers during analysis,acid build up and a subsequent drop in viscosity signaled breakdown..oil looked like black water..not arguing your findings,its entirely possible to fail 'up' the chain..my history is almost 100% diesel.