Oil pressure issue

[miksebik]

Hi, I have an oil pressure gauge installed.. Its not the Nexsys, I have a mechanical gauge in my middle vent..
Last 1000km I noticed a weird behaviour, when the oil pressure went to 20ish, when the oil warmed. I noticed this for the first time after I used the 5W60 oil. As I thought it was rubbish ("racing" MOL oil), I switched to Motul 300V 10W60. Before I used 5W50 but due to oil consumption (1L per 1500-2000km) I wanted ..W-60 oil.
So with this 10W60 it improved a bit, not by much. Yesterday what freaked me out was when I saw the needle going below 20PSI! As I was driving in downtown, I tried to hold higher revs even when waiting at lights.
I reflashed the ECU, raised idle to 1100. This returned me to cca 30PSI at idle. Thus I got home but saw that during acceleration, the oil pressure did not raise like before.. getting to cca 50PSI at 3000rpms.
In the garage I saw the idle (1100rpm) pressure dropping under 25PSI again.
Fortunately I got no low oil pressure code / warning.
So what next? My plan is to measure the pressure with manual hydraulic gauge to compare it with my gauge. We will check the oil filter for any metal.. I can also get oil from the oil filter housing to have it analysed (for petrol / metal particles). These would be the steps before dropping the oil pan and replacing the oil pump.
I also got a hint that my rod bearings (replaced 35k km ago) were being destroyed due to faulty injectors...
What else could have gone wrong?
Thanks!

 

[miksebik]

this is the video where oil pressure gauge reacts lazily to the rpms.

 

[AzNdevil]

these cars idle at very low oil pressures. generally speaking 10psi per 1k rpm is fine
im using fuchs race pro s 5w40, idle@28C ambient with a/c on is around 20psi@90C oil temp
at the track after an event, idle@26C ambient with a/c off, 16-18 psi@130C oil temp

ive used thicker oils before like 10w50, it does raise the oil pressure a few psi but car felt really sluggish especially in high rpm range

 

[miksebik]

So we checked the oil filter and unfortunately the oil glitters a little - there are very tiny golden particles, no big metal shavings..
The next step will be to replace the oil pump and (check the rod bearings) as that one is to blame.
Any idea where the golden particles are from? VANOS, turbos, oil pump...?

 

[AzNdevil]

ok that sucks..... bearings are a common issue on these cars.....but so are ringlands but then it will be smokey
these mechanical oil pumps dont fail like the ones in e36/46 m50/52/54 so if it was me i'd look at bearings first

 

[miksebik]

new discovery! compression on 4th is 5bar while on the others is 9-9.5 bar.
Anyway its weird that the engine ran completely normal. No misfires, full power (unless it lost pressure abruptly during last few kms).
According to a shop the culprit can be the rod bearing on 4th which would allow lower compression. Is it even possible?
Tomorrow they will do the leakdown test.

 

[AzNdevil]

new discovery! compression on 4th is 5bar while on the others is 9-9.5 bar.
Anyway its weird that the engine ran completely normal. No misfires, full power (unless it lost pressure abruptly during last few kms).
According to a shop the culprit can be the rod bearing on 4th which would allow lower compression. Is it even possible?
Tomorrow they will do the leakdown test.

the only way i can think of a bearing causing loss of compression is that it spun or is very very worn to the point where the piston rings cant expand enough to the cylinder walls.....but i'd say highly unlikely cause the engine would be rod knocking hard

however.... your rod could be bent causing loss of compression, which could be confirmed with a borescope

 

[miksebik]

the only way i can think of a bearing causing loss of compression is that it spun or is very very worn to the point where the piston rings cant expand enough to the cylinder walls.....but i'd say highly unlikely cause the engine would be rod knocking hard

however.... your rod could be bent causing loss of compression, which could be confirmed with a borescope

yes.. bent rod would make sense.. but I still do not get it how the engine could run so strong (560HP) with a bent rod and low compression without any issues like misfires / knocking.

 

[JohnDaviz]

Just what i have on my car:

Cold pressure at idle is high at 70-90psi
Hot Idle is the lowest i read at 48psi
At 3k rpm with a hot engine i am at 90psi

This is from an engine running 3k miles from new with biggest tolerated main bearing gaps and 5w50 oil.

At 100°C the viscosity is not far away from thinner oil as i mixed it to my own spec.

 

[suebf]

You mentioned that the rod bearings were replaced 35,000 km ago, but you also received a tip that faulty injectors might have damaged the bearings. Bad injectors can lead to improper fuel delivery, creating abnormal combustion and excess heat or force on the engine components. This could result in accelerated wear, including on the thrust bearings. If you suspect injector issues, it might be worth running an injector balance test or having them professionally cleaned and tested. If the injectors are malfunctioning, it could explain the premature wear on the bearings.