NCDiesel & All --

Well, I rummaged around in my trash can and found a genuine Isuzu oil filter from an '84 diesel P'up. I think these are the same as used on the Trooper TD. I cut it open and found that there are no valves inside other than the rubber flapper check valve for the inlet ports.

But this is a dual filter:

-- A normal full flow filter which filters most of the oil from the pump and delivers it to the oil gallery.

-- And a 'bypass' filter which filters a small part of the pump output through a very fine filter and delivers it through a small ( .028" d ) orifice back to the crankcase.The orifice is in the cast aluminum filter base. See my earlier photo of the base as I am adding an arrow to show where the orifice is located.

OK, the O-ring. This used to seal the full flow filter outlet from the bypass filter outlet. If it is missing, I think that air from the crankcase would flow up through the orifice to the bypass filter outlet and 'leak' (without the O-ring) to the full flow filter outlet and so allow the oil to drain back down through the pump to the crankcase. Hot oil would drain faster.

I have two photos:





NC's post of the oil flow chart for the TD supports what I have described except for the .028" orifice which is not shown. Unfortunately, this image was converted to a link which brings up the timing for a John Deere Model A tractor.
Randii??

I realize that what I have here is not the same as what others have said in previous posts so feel free to respond.

And, the oil cooler is a stand alone device as far as the coolant is concerned and can be separated from the oil filter base without coolant loss.

Paul