When natural gas powered engines were used in Milton several years back for garbage trucks, the maintenance people noted they lasted longer than expected because the oil stayed cleaner. (The police department didn’t like them because they didn’t have as much get-up-and-go as gasoline.”

From
http://alternativefuels.about.com/od/generalmaintenance/a/gaspropanemaint.htm
“The accumulation of unburned fuel, soot and acids are the major contributors to the breakdown of motor oil. It’s not so much that the oil itself “wears out,” rather it’s the depletion of additive packages from the cumulative effects of time and mileage that renders the oil ineffective. When motor oil is kept relatively clean, the anti-oxidants, anti-scuff compounds, viscosity index improvers (and myriad other additives) don’t take such a “lickin,” so they can keep on “tickin.”
“One of the biggest benefits of natural gas and propane as automotive fuels is their clean burning characteristics. Both fuels burn so cleanly that not only do they produce scant tailpipe emissions, but they also release virtually no by-products of combustion (carbon particulates and acids) into the motor oil. “

David for longer engine lives
and lower costs in human lives

But the headlines should be big if one of them ever goes off.

Implementation of a good technology. The NG will be drier(no oil) than the diesel and will shorten the life of the rings and valve guides, seat, but considering the emmission
contrast, the maintenance cost are well worth it.