Interesting issue concerning oil pressure on my 2006 Monterey with the CAT C9 400HP engine. Had the coach in the shop (Cashman Equipment, Sparks, Nevada) for a valve adjustment. After the adjustment they checked the codes with their computer and it said it had 172 issues of "Low Oil Pressure" within the last 368 hours. There was no check engine light and no codes when queried through the smart wheel. Supposedly the check engine light will come on after an oil pressure reading below 18 PSI. My unit runs between 35 psi and 45 psi when driving and as low has 24 when brought to idle after driving.
The service manager did come checking and found a Truck News Bulletin (similar to Tech Bulletin) that CAT had oil pump failures on the C9 and in 2009 they released a new oil pump design. Typical design engineers, not only Roadmaster, they placed a bracket in such a manner that you cannot just drop the oil pan. After an hour (2 techs working on it) they had to drop the oil pump pickup and the oil pump (into the pan) so that they could slide the pan to the side and finally remove it. Not easy when working through a gap of about 5" between the top of the pan and the bottom of the block.
We then inspected the pump and sure enough, there was definite wear on the piston and the pump housing. The design has a polished steel piston in an aluminum casting. Who the heck uses two moving parts with such a difference in hardness, gee, ya think the aluminum will wear, duh!
The main point here is that these pumps will eventually fail and you probably won't see it until it is catastrophic. Next time you're in for service have the computer check done to see if you can catch this before it completely fails. The new pump is $380.00 and it looks like 4-5 hours at $145.00 an hour.
