Way back when everyone freaked out about the whole Y2K thing, the bank my dad worked for decided to get a generator for back-up power should they need it. They bought it used from a hospital with about 600 hours on it. The bank so far hasn't had to use it except to test it and run it once in a while, so it has very few new hours on it. The oil and coolant are sampled twice a year, and I know the oil is changed yearly even if the analysis looks good. I have five oil analyses from may 2002 through June 2004.
This is a Cat model 3306 diesel generator. I don't have exact records, but it sees about 6-10 hours in an entire year, with about half that at each mid-year analysis. It appears that the oil is changed at the end of a calendar year when the oil is sampled, and Cat 10W-30 is used.code:
Item 5/6/02 12/3/02 6/11/03 12/18/03 6/4/04
Pb 1 1 0 0 0
Sn 0 2 0 0 0
Fe 3 3 1 2 1
Cr 0 0 0 0 0
Al 1 0 1 1 1
Mo 0 0 0 1 0
Cu 2 2 0 1 0
Na 3 0 0 3 1
K 1 0 0 0 0
Si 7 6 6 7 5
Ba 0 0 0 0 0
Ca 1660 1759 1428 2046 2440
Mg 320 315 253 413 330
P 820 884 732 1067 1191
Zn 906 929 780 1185 1326
Soot NO NO NO NO NO
OXID 20 22 27 16 17
SUL 0 8 0 9 0
NIT 0 0 0 0 0
FUEL N N N N N
ANTI N N N N N
H2O N N N N N
V100 11.4 11.5 11.3 11.1 11.8