Why does everyone say 30 minutes of idle time is killing your engine?

I was reading through a fleet maintenance report from a company out in Casper, Wyoming that tracked 40 trucks over two winters, and the numbers did not match what I keep hearing in the shop. The trucks that idled the most actually had fewer cold start wear issues than the ones that got shut down and restarted all day, mainly because the oil never cooled off enough to drain back and leave the top end dry. I always figured idle time was just wasted fuel and soot, but seeing 12,000 hours of data saying otherwise made me rethink it. Obviously a deleted truck sitting there for 8 hours is a different story. Has anyone else seen actual oil sample numbers on this or is it just me?

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angela_grant1mo ago

Wait, doesn't the wear mostly depend on how many times you actually cold start the thing, not just how long it sits? I've seen oil sample numbers from a few of our trucks and the iron and lead were always worse on the stop and go routes, not the long idle ones. Sounds like your Wyoming report is backing up what I've been saying for years.

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