Best Mileage to Change Oil Pump on DD15?

Most of the issues with oil pressure on the dd15 is caused by the suction o-rings. If it where mine, and I've maintained the O-rings, and oil pressure is good. I would see no reason to change the Oil Pump until it's due for bearings. And more than likely, you'll have a different issue (oil consumption, etc.) that will cause you to say "let's go ahead and do the bearings and pump while your in there".

In my experience, if the dd15 didn't have the suction housing and O-ring issue, the bottom end of the engine is very well built.

 

Like I said, it really all depends on how well the oil and oil pressure has been maintained over the life of the engine. I've seen the oil systems/bearings fail at 750k ( cratered the engine), but they had never had the suction O-rings replaced...

When you start the engine cold. If the oil pressure jumps up to the max and stays there. The O-rings are fine. If it jumps around on it's way up there, then they are due for replacement. If that rule has been followed its entire life, the bearings and oil pump won't be due until it needs an overhaul.

There are a lot of guys that say 1million miles is a good time for a lot of PM repairs. I'm more of the make sure you have the money stashed when the engine has 1 mil, but keep running it till you see a sign, ( reduced power /fuel mileage, oil consumptions /blowby, etc) especially if you own it and drive it, you're probably watching things close enough to know.

 

Most cases an engine won't just suddenly fail. There'll be symptoms. Honestly if you get to 1 mil I'd just budget for a complete overhaul and run it until it starts showing its age (oil pressure at bottom end of spec, oil samples come back indicating something wonky, burning oil, blowby etc).