I started a thread several months ago on my new/old '06 F350 DRW 6.0 that only had 28k miles on it when I purchased it last March.
http://www.montanaowners.com/forums/...ad.php?t=55321
I thought someone had posted a comment there that made the most sense to me, but I can't find it - basically that the 6.0 (made by another company) was intended to be a school bus engine, and not have all the emissions & oil cooler added on. Problem was the maker wasn't all that careful about flushing out the casting 'sand' before assembly and some engines had enough to clog the EGR and oil cooler. This obviously causes decreased oil pressure and increased temps, and nasty other results. If you look up comments on Ford Truck Enthusiasts or The Diesel Stop, you'll find people who've deleted the EGR and replaced head bolts and oil coolers to keep from having problems. While I could do all that and still be way ahead because of the price I paid for it (replace the whole engine too!), I opted for a thorough coolant flush and an aftermarket coolant filter kit. There's also some comments about Ford coolant having 'silicates' in it that I really think are left over from casting and not from the coolant itself. Almost 6k miles later and mine's still going strong - and the coolant filter hasn't clogged yet (you can tell its clogged when it doesn't get hot with engine temp.). Figure I'll change it with the next oil change come spring.