My bus was rough starting, blowing smoke for a little while, someone said it was due to low compression. The smoke was white but smelles like diesel, not coolant. I got the glow plugs replaced, and the relay. Some of the wiring on the realy was so bad it basically was doing nothing. Starts like a dream, like my girlfriends corolla! Runs great, great power, never overheats, infact it runs a little cool which i need to get checked out, but better than runninghot! What are the typical signs of engine wear/low compression? Collant out the tailpipe on start, hard start, runs rough? anything else. I have none of those right now. Checked the oil, no foamy bubbles, checked the radiator, no oil bubbles at the top!
Ive seen both 7.3's and 6.9's with 8-900,000km on the clock, even with a lot of blowby they will still run well, maybe slower to start when cold due to lower compression, but nothing to be overly concerned about. You can always switch to a thicker oil to slow oil consumption.
Valve guide wear and cavitation is my biggest concern with the 7.3l