I'm going to cut straight to the chase before I say anything else:
THE ENGINE IS NOW FIXED!I was going to post earlier but I had to make sure it was fine by doing some endurance and stress tests, and after roughly 60 kilometres (37 miles) of driving I am fairly certain it's fixed.
I'll just mention a few things about the reassembly job before I go into detail about what caused the low oil pressure and costs/time etc.I got away very lightly with screwing in the wrong bolts in earlier - The correct bolt (which I screwed into the hole marked WT) was barely even scratched from being inserted into the wrong thread. The thread it was screwed into looked slightly mangled, but nothing a little threadlocker couldn't solve. If anyone is using this post as a guide, always remove the
pump mechanism sprocket, not the balance shaft sprocket, and make sure you put the in pump chain tensioner and sprocket simultaneously, as otherwise they won't fit.
Once the bottom of the engine was assembled back together and filled with oil, I cranked it without the coil packs plugged and the HPFP fuse out, to circulate the oil around. Then came the nervous part of actually running it. It ran rough for about 3 seconds, then became smooth. All perfectly normal behaviour.
After about 15 minutes of running at idle, an oil drip developed from the pressure switch area. After a further 10 minutes it started trickling, so I shut the engine off. The pressure gauge showed 20 psi with the oil not fully warmed up, so the bearing change didn't affect the oil pressure, which is what I expected. I will go into detail later about the correct specs for oil pressure.
I've circled a free-spinning part of the gauge where the leak most likely came from. It lost about half a litre of oil through this connection.
Upon putting the new pressure switch back in, no more oil leak, confirming the gauge was at fault (although there is a minute oil leak from the vacuum pump).
After letting the car warm up I did some harsh test driving, and I would hold the RPMs at 1200-1500 after giving it the beans to gauge if the pressure is good. If the pressure was bad, it would toggle at these RPMs. I then did an endurance test of 30km on the motorway to see how it would hold up on a longer journey. Neither of these tests made any lights pop up, and the engine sounded perfectly smooth.
Now the car has failed the NCT (Ireland's version of the MOT) on the two front rearmost wishbone/control arm bushings and the rear discs, as the pads are not fully touching the disc due to a lip on the disc. Not a bad verdict as it could failed on so many other things, considering it's dodgy history. I'm having my mechanic friend (same one that was with me when I bought the car) change out the previously mentioned items, and the NCT is now booked for this coming Wednesday.
THE VERDICT: Unofficial oil specs from an Audizine forum post are as follows:Idle 1-1.2 bar or (14.5-17.4 PSI )
2000 RPM 2.7-4.5 bar (39-65 PSI)
3000 RPM 3.5-4.5 Bar (51-65 PSI)My car achieved (on 5W40): Cold Idle: 55 PSI
Hot Idle (After harsh driving): 16.6 PSI
I don't remember the measurements for the PSI at higher RPMs, as it was the idle oil pressure I was concerned about.
If your pressure is lower 17.4 - 23.2 PSI @ 1200RPM/1500RPM for over 0.5 seconds you will get a low oil pressure light that will disappear if the pressure improves. If it remains in this condition for over 1.5 seconds then the oil pressure light will stay on no matter what RPMs you are at (I have conflicting info about which RPM the ECU polls the pressure switch at).
The oil pressure switch is not polled by the ECU at idle.
What caused the low oil pressure for me?To be honest, I'm not 100% sure, but I think one of these or a combination of these was the culprit:
Faulty PCV: With the Oil Filler Cap off the RPMs didn't drop, indicating it was faulty. AFAIK, this causes too much crankcase pressure, putting strain on the pump, reducing oil flow or something like that.
Over-filled Oil: The oil in the car was overfilled when I bought it, which strangely enough can cause low oil pressure.
Blocked Pick-up Pipe: The pipe itself wasn't too blocked, there was some dirt/sludge around the edges. I found some broken off plastic pieces in the sump that had broken off the oil pump chain guard, likely from when the balance shaft sprocket bolt sheared in the past. These could've floated into the pick-up temporarily blocking it.
The oil filter was also old and filthy, but nothing that would stop oil flow.
Changing out the connecting rod bearings didn't affect the oil pressure, so it definitely wasn't those either.
I inspected the oil pump when I took it out and it was perfect, bar the scars from the balance shaft sprocket coming loose in the past.
So how much did all of this work cost?€1,115. This cost includes 2 torque wrenches, about 20L of different quality engine oil, at least €150 of just VW stretch bolts, engine components and expensive shipping fees from the Czech Republic.
All of the work was done by myself and the help of a friend, so none of this cost includes labour. If a mechanic were to do the same work I did, I assume the total cost would be €2500+.
And how long did it take?Roughly 3 months, or about 100 hours of my spare time lying on the ground under the car. I could've had it fixed by the start of October had I known the oil pressure specs before diving into the guts of the engine.
That's all from me. I seriously owe you a pint
@Pudding for your help in all this.