What did you get $$$ out of your sled since I have one with 4K miles on it and what did you upgrade it with?  If you do not mind me asking..

 I am thinking of buying a 600 sdi renagade X for my next one or seeing what comes out new from cat in the 4-stroke....possibly a Yamaha Apex.??? I have heard of quite a few 800 Power Tecs squeeking a piston and the Mach is a bit of a pig in the trail ...simular to my old ZR900. 

Interesting thread. I've been thinking it is time to "upgrade"  my 98 & 99 670 MXZ's, but I have a gut feeling that these series III engines are not even in the same ballpark as the "old" rotory valve ones. I've got 8000 miles on 'em, with new top ends at 5000 and a crank brg at 7000. 15 mpg isn't too bad either. IF Skidoo could drop the "old" engine in a new frame, I'd jump on it!

I blew mine up going accross a lake wide open.  2005 600 SDI Renegade.  Totally stock, no mods, premium fuel, small amount of isopropyl in the gas (which I always do religiously when real cold).  The sled used lots of oil so that wasnt an issue.  Dealer could not find a problem, but one piston burned bad and the other one was starting.!!!   I didnt' think you could do this to a 600 SDI but apparently you can.  I have burned my share of pistons on carbed sleds mostly my fault being too lean etc. but never thought this would happen to me.

600ski is the most reliable snomobile you will ever have because i have one and it never broke down