XXL asked if any of us ever actually had an engine failure from the choice of oil we used.
I can say that I definitely did. When I was in my teens, in about '58, I rebuilt a '55 235. I was very careful to use the best of parts available at the time and sweated blood over getting the tolerances as close to factory specs as possible. It was bored some, with new oil pump, a mild cam and valve springs from McGurk, headers, larger single barrel carb, etc, etc. When I was about ready to start it, someone recommended that I use 50W racing oil in it. Not knowing any better, that's what I put in the engine. At about 900 miles, the engine spun a rod bearing, turning the crank blue and ruining the rod as well. Some of the other bearings showed damage, too. I'm lucky it didn't throw the rod and bust up my block. I learned that when you use thicker oil, you should build the engine for more clearance. After a re-rebuild, I used used Sinclair detergent 20W. ('55 Chevy recommended 20W summer and 10W winter, but in Florida We used 20W year around)
That engine lasted me for 10 years and was in 3 bodies. It probably had around 100,000 miles on it when I sold the last car with it in it, in '69. Of course, it was MY fault, not the oil's.
So, If I had used the recommended oil with factory slearances, I never would have had to do the rebuild over again!
