Valve grinding compound is the most destructive substance tested by an enormous
margin. Silicon carbide suspended in a carrier is engineered to grind metal,
and inside a running engine it grinds everything at once: it knocked within a
minute, seized in 2 minutes 7 seconds, would not restart even on starting
fluid, and produced the worst cylinder scoring of any engine here with the
piston rings welded solid in their grooves. Adding it to an engine already
full of aluminum anti-seize made things worse, not better — 39.4 seconds, and
the rings seized regardless.
The two contaminants that matter in real life are the two that came from the
oil analysis report. Steel shavings killed an engine in 100 minutes by cutting
deep grooves into the cylinder, scoring the crankshaft, and finally breaking
the oil-slinging arm off the connecting rod cap. Dirt and sand took just over
two hours and did it differently, sanding metal away evenly rather than
gouging it, which left the cylinder in better condition but opened valve lash
to roughly three times specification. Both engines were destroyed. Neither is
exotic — that is iron from normal wear and silicon from a compromised air
filter, in concentrated form.
Two results run against expectation. Aluminum anti-seize was the least
destructive additive tested: still quiet, still smoke-free, and still running
at 118 minutes when the test was deliberately ended, though the oil by then was
thick with aluminum glitter, so wear was clearly happening slowly. And sugar,
the one everybody has heard about, did essentially nothing — heavy doses twice
over, an hour of normal running, no smoke, no noise, and a successful restart.
Its only measurable effect was pull force rising from 22 lb to 31.4.
The useful conclusion is not about additives at all. Four of these engines were
destroyed by ordinary contamination — metal from wear and dirt past a filter —
in under two hours at extreme concentration. No oil filter captures everything,
and no air filter stops everything. On a modern engine oil, what wears the
engine out is generally the contamination in the oil rather than the oil
itself, which is the argument against very long oil change intervals and for
staying on top of the air filter too.