I have recently acquired a 1993 5 Ton GMC Topkick with a 3116 Cat, with the mechanical pump. Not sure what hp rating it is just yet... I realize that this isn't Cat's best engine, by a long shot; but its running pretty good aside from being a little rough and grumpy when started cold and the oil changes were done regularly with records. It has 550km on it (km, not miles). Im wanting to know what some of the do's and don'ts are in regards to maintaining these things. Do they like to be revving high under load or are they a lower revving engine? 15w-40 oil? Any fuel conditioners required? Any specific maintenance things to consider with them?