MC engine - low oil pressure...Update 2

[EBavely]

Hello all...

Ok... I just did some more testing last night.

First, before putting on the pan again, I switched the 5kt oil suction tube
for my known good 4kq unit.  I also plastigaged a main bearing and a rod
bearing.  Both bearing clearences, as expected were WELL within specs... The
clearance seem to be right where they should be in a newly rebuilt engine.

Next, per Marc's suggestion, I went out and got two AN-8 caps and capped off
the bypass for the oil cooler lines.  I then put the oil pan back on, filled
it up with oil and started the engine back up.

When I ran the car, I noted the same exact readings on the gauge as before
(after changing to the German filter)....no change.  Same deal... 75 psi or
so at cold idle, then after it warmed up, idle pressure moved down to about
30 psi, then finally to about 10 psi.  When fully warmed up (fan has come on
and off), the pressure will not get past about 35 psi when reving the engine
to about 3500 - 4000 rpm.

So, from this, I conclude that:
-It's NOT the bearing clearances
-It's NOT the oil cooler circuit (length of lines, air, tempostat, cooler
obstructions)
-It's NOT the pickup tube sucking air or blocked

The only two things left for me to doubt are the oil squirters and the oil
pump itself.  I don't know what the problem could be with the squirters
unless they're stuck open and bleeding off a ton of pressure.  The Bentley
does say that the squirters regulate oil pressure at idle and *should* only
open above 35psi (might be wrong about the exact figure).  Do these things
go bad?

I'm leaning towards changing the oil pump based on the pressure when cold.
Could it be that when the oil is thicker I see higher readings, but when hot
and the oil is thinner, the used pump might have a problem trying to
maintain adequate pressure?  I really didn't think the pumps had any
problems on these engines.

Speaking of oil, what is the ideal oil for these turbo motors? Others have
suggested that I'm using the wrong oil. I put in plane Jane 10W30 Castrol
for the break-in period.

Next, I'm wondering about the setup of my oil pressure switches.  ET_KA
shows the two switches (the brown/black 0.3 bar unit and the white 1.8 bar
unit) in varying positions.  It shows that on the 4kq the black 0.3 bar
sender in top hole and that on the 5kt the white 1.8 bar sender is in top
hole.  Does the position of these senders matter at all?

The reason I ask is that I have my VDO gauge sender (two pin for gauge and
warning) in the top hole... Just wondering if the placement of these things
makes any difference.

Thanks again... Unless I have reason to think otherwise, I might be changing
oil pumps this weekend....

Elliott
86 4ktq
83 CGT
81 Coupe ITB
88 80 Fwd
Bunch of other VAG products