Oil pressure issue.

[dhirocz]

Developed an odd oil pressure issue that I need to address. I've got an 871, @m*m^2, 898k miles on an original engine so yes, she's showing her age.

Last couple of days I've developed a significant change in oil pressure. No leaks or noises but about a 25% reduction in pressure. Hot idle went from 20 to 14. Cruising RPM pressure has dropped from about 40 to 30...oil pressure starts at 42 and over several hours the oil pressure will drop about 10 psi. If I stop and let it cool it comes back up to 40 and we start all over again.

Oil pressure does tend to 'surge' over 35 during initial acceleration and settles back down which makes me think it might have an internal oil leak or maybe an issue with the oil pump pressure relief/bypass.

8k on this oil and filter change. Fleetguard filters. Oil is still amber. I still run a bypass filter. 6 dimes at 685k in the pump, which is when I also did a bearing roll. I add a gallon of gear oil every oil change. No check engine lights or other alarms, no functional oil temp gauge in the truck.

2 days ago I took it on a 400 mile trip and it was a gallon and a half low...well beyond acceptable...no significant leaks found, and I don't push my truck hard. Today it didn't loose much of anything, same route. I have developed a significant loss of power and mileage lately as well that I've written off as being a result of being close to an inframe.

This engine normally cruises at 45psi on a fresh oil change, and drops to the high 30's when I get close to my 15k change interval.

Do these symptoms ring any bells for anyone? What is alarming is how sharp the reduction has been...it was fine just a few days ago, which tells me this isn't due to a loss of oil viscosity but some sort of other issue instead.