Strange Oil pressure

[rallydiesel]

Who rebuilt the engine?

[92EcoDiesel Jetta]

The symptoms:
I've got a rebuilt engine (MF block, new AAZ head from boraparts) that cannot seem to make oil pressure when hot. At cold startup the gauge goes up to 7 bar, pretty quickly dropping down to 4 bar. The warmer the engine gets, the lower the pressure gets, until at hot idle it's reading not quite zero, but 1/4 bar maybe, with the oil light on. Worse yet, once it's hot, at idle at traffic lights and such it makes this metal squealing noise like wear indicators on brake pads. I cringe imagining the turbo machining itself... I've been feathering the throttle to bring the idle (and pressure) up and the noise stops.  Driving when hot, the oil pressure is 1~1.5 bar. If I really get on it it will go up near 2 bar but that's about as high as I can get it.
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I remember a post of a beautiful looking completely rebuilt 1.6 NA engine with squealing sounds. In the end it turned out the rebuilder used the wrong oil pump.

[libbydiesel]

There are both mechanical and hydro MF blocks and there are also both mechanical and hydro ME blocks.  MF blocks have oil jets, ME do not.

[air-cooled or diesel]

you shouldn't run it until you get oil pressure, you may have already hurt parts running at too low oil pressure. your losing oil pressure somewhere, the question is where. if your running 15w-40 you should have a lot of pressure in the head. if its dumping oil back into oil pan you need to trace where. im bearings / im pulley, main bearings, rod bearings are places to check. puralator filters suck, napa has wix for a good price.  pull vac pump and look around, look at gears , im shaft/gears, oil pump shaft, etc. make sure vac pump turns freely and the gears and oil pump slot are in good order, turn oil pump and make sure it moves freely, turn im shaft with vac pump removed and observe. does pulley / im shaft have key? is pulley tight? im shaft end play? check turbo oil lines and return line. it could be dumping oil thru the oil filter flange / oil cooler back into to oil pan too. it could be blockage to oil passage to head, wrong head gasket? or hole lined up wrong?
checked pump so hopefully that will not be the problem; is relief valve closed??
can you hook up oil gauge to flange and get reading from there? hot/cold.