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Discussion Starter · #2 ·
OK, think I've worked out what is happening.
Have been testing the return flow characteristics of a spare oil filter and there is a non-return/reverse flow feature built in, so the oil is not flowing back through the filter.
My conclusion is that item 13 is an oil-filter bypass valve and it has stuck open, meaning oil not pumped through filter so pressure higher due to greater flow. This would also explain the oil draining back out of the engine as non-return/reverse flow feature bypassed too.
Now to obtain the spring, valve and seal or equivalents. A friend is landing in Italy tonight and is going to ask at local dealer. Fingers crossed....
 

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Discussion Starter · #3 ·
Good and bad news, after endoscope view today.
Good news: the issue is indeed the oil filter being bypassed by the bypass valve.
Bad news: is it just me or has the bypass valve come down further than it is supposed to? If it has, does that mean the shaft it sits in is broken? The view is with oil filter off, looking down what would be the top left side of its position. The wall on the right is the outside of the shaft the oil filter screws onto, though too far in for the thread to be seen.
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In any case, I can see that whole mounting will need to come off, which means drive shafts out too.
BTW, the oil filter was effectively dry inside - just the bit of oil I put in before fitting. In fact the whole area look remarkably (scarily) oil free.
Alfa 164 24v 3.0 1995.
 

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Discussion Starter · #4 ·
After looking at pic from inside oil outlet from oil filter, have noticed this is actually plugging the side outlet from it - so might be in the right place. The hole on the left of the pic below relates to the right side of the valve above.
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I have no idea what the thing on the right is. Might be an outlet to the oil cooler.
Going to take another look tomorrow and try to get more revealing pics.
 

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Discussion Starter · #5 ·
Took more endoscope pictures today and understand the oil flow better now.
Took off the 'made in China' OEM filter and put on the 'made in Italy' OEM one. Slightly lower peak oil pressure when cold - up to about 0.5 bar (7psi) lower. The fact it is different at all indicates to me it is now flowing through the filter material, rather than just through the filter's bypass valve. The oil pressure seemed to come down to more normal readings faster and behave more nromally when driving - even before normal water temperature was reached. Remember that previously it took much longer - until normal oil temperature was reached.
Have some confidence will no longer have zero start up oil pressure when try it tomorrow - the biggest test. If there is still an issue there I won't think it is the filter unit at fault but that valve on the side. I finally understand that if that valve is open or leaking, some/all oil will bypass the oil filter itself and go straight around the engine - as well as being able to drain back into the sump when engine stopped.
Taken me 2 months to finally understand the system as literally zero details out there. Will post results after start tomorrow.
 

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Discussion Starter · #6 ·
Just started car after sat overnight and, after fired, oil light stayed on for 1 to 1.5 seconds before oil level began to rise. While this is an improvement over the 'made in China' filter it is still not ideal or what I would consider normal.
The new oil valve, item 13 in the diagram above and the thing on the left in the photos, is due to arrive in a few days and will be examining it in detail.
There may be a tiny bit of debris leaving it slightly open, which could allow some reverse oil flow when parked and some oil filter bypass flow (resulting in higher oil pressure) when running.
Am tempted to use the side-view mirror atatchment on the endoscope but iit it fell off it would drop deep into the engine.
Will post again when valve arrives.
 

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Discussion Starter · #7 ·
Does anybody know the approximate size or anything about the spring, item 14, in the diagram above? Part number: 73503073
I am wondering if this has got weak with time and allowing too much oil through bypass valve 13. If I knew roughly what size/strength I could look for an equivalent. Thanks.
 

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until you can confirm with a mechanical gauge that your oil pressure isn;t what you want -- I wouldnt do anything, The gauges sometimes stick in the dash....The senders are not super accurate....
 

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Discussion Starter · #9 ·
Agreed the gauges are not necessarily accurate but defo not stuck and will get that side of it checked mechanically by the garage when it goes in. The fact it displayed some 40psi higher after the oil change indicates some significant change beyond fresh oil/filter. The biggest concern is the zero oil pressure at start up, agreed by both gauge and warning light so very likely the actual case.
If I could get a rough idea of the item 14 spring size I could buy a pack of springs around that size and the garage could do a 'best fit'. My current thinking is age has softened the current spring 14 to the point where the oil bypass valve allows both oil past the filter when running - leading to jump in oil pressure when running, and back to the sump when parked - giving the zero oil at start up issue.
 

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Discussion Starter · #10 ·
Just to share the latest development. The new valve, item 13, arrived today. Or rather the box it had been in did. Some small hole in corner of box, from transit or customs, seems to have let it drop out - all other, less important, parts were still inside. Naturally the most important part is the one that had to be lost. Seller checking to see if can find another but not holding my breath. Either way, car going into local Alfa specialist on 5th Oct and will just have to hope a strip down, clean up and rebuild get everything working normally again. Will let you know.
 
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