Yes, another low oil pressure R53, but read on if you can...

I purchase this car used, auction. It is my third Mini. 2003 R53, 108k miles. Not as much fun as my '11 JCW, but maybe when I am done with it. Wanted something to play with, and the body and interior is solid. I run mostly Audi TT's, kind of getting tired of over engineered German pieces of ... so decided to try an overengineered british car. My TT, running 320hp+ at the wheels on my second engine rebuild just blew a head gasket at 190k miles, so its time to find a more ... reliable? ... fun daily driver.
Knew it didnt run. Carfaxed it, shows it was regularly dealer serviced up to 5k miles before I got it.

Problems included:
- Someone hacksawed a hole in the bottom of the exhaust pipe closest to the engine, hammered out the matrix - assume it was vandalism, but could've been PO (replaced exhaust manifold, cat with CARB compliant unit)
- Cracked oil pan - but happened during transport. Forklift driver drinking one too many rockstars. Replaced, new oil pan gasket. Bottom of engine was spotless, no metal in oil pan. "suspiciously" clean, although to be fair, the oil had been changed just prior to my purchase. Installed used, good condition, OEM oil pan.
- Green goo (dexcool?) in coolant tank - clogged oil cooler, one hose, heater core. Replaced oil filter housing, heater core, cleaned red sludge out of one hose, flushed system about 5 times. Have heat again, oil cooler lines show good flow as does radiator. All good? Now its blue... All components OEM, from dealer. Oil filter housing is new design, no missing center plastic bit
- Oil leak from front of engine - replaced O-ring on crank sensor
- Slave cylinder was leaking - fixed, went ahead and purged/bled brakes and clutch system. Used FTE replacement, same as on the car
- Replaced oil pump (after continuing to work this issue), OEM from dealer
- Noticed supercharger mounting bolt missing, replaced.
- One transmission mount bolt stuck about halfway, fixed. Was someone trying to pull the engine? Dont know, it appears to be the original engine.
- Had several codes - catalyst (no surprise, and gone now), and readiness will not pass. Everything ok, except for components is in process, probably have not driven enough (300 miles) and definitely not been driving it hard until the oil issue is fixed.

Car runs well - no rattles. Good acceleration, drives the same as my last '04 MCS, now no oil or coolant leaks.

During the oil cooler repair, I found this funny green connector not attached (oil pressure switch). Plugged it in after replacing the oil cooler - and when warm only, at idle through ~ 1500 rpm. I have the pressure warning. Oil pressure is ~3psi when at idle, > 20psi when warmed up and > 1500rpm. Replaced the oil pump anyway.
Put the original oil pressure switch in, pulled from the original oil filter housing assembly with the clogged oil cooler, no change.

Now the light is on only at idle, any increase in RPM it immediately turns off. Tried 15w50 oil, no change [wanted to see if the pressure switch action changed in any way with heaver weight oil, plan to pull the oil pan anyway and return to correct weight oil].

Here is what I need to do:
I am pulling the oil pan off (again) and will pull the oil strainer to see if it was bent / dislodged, or full of sludge - I dont believe so, since everything was so clean, but worth check. Also looking for any observable signs of bearing issues, doubt I can see anything.
Also need to check compression and do a bleed down test - figure if something is really out of whack, maybe some metal got through the system, although no signs of it.

So I believe I covered all of the 'simple' fixes found in the forums. Did I miss anything?

Not sure I have the time to pull the engine and replace bearings, but if thats what it takes...? I do all my own engine work - not afraid of this design, just no time to do it right now.

Appreciate any input you have! Would hate to pull the engine apart only to find the bearings are fine and it was something simple.

 

Sorry - I should have added that both the original and new oil filter housing are the new style - no missing plastic bit in the center of the filter.

 

Have you plumbed a mechanical gauge to read oil pressure?

I've seen faulty pressure senders, I've seen pressure senders that had ungodly amounts of pipe dope on them that caused problems, and I've seen the pressure sender wiring caught between the engine and trans due to someones neglect during a clutch job.

Are you running factory oil filters?

 

I ran two different oil pressure switches - no difference. I have a manual cheapie oil pressure gauge (china freight) and it reads right around 3 psi warmed at idle, but better than 20psi when >1500rpm or so.
Wiring is good - its definitely not shorting - did a visual inspection when I had the exhaust out, also ohmed it out.
Yes, running factory oil filters. I have tried three different ones out of an abundance of caution - no effect.

Thank you for the suggestions! Have not had a chance to pull the oil pickup yet, but I suspect I wont find anything.

I neglected to mention I am at the full mark on the dipstick, and that was adding just under 5 qts...

 

May I suggest the obvious? Run a compression test with engine at operating temp.

 

Obvious:
Compression test, engine warmed up to operating, immediately after 10 mile drive
1 = 125psi
2 = 110 psi
3 = 123 psi
4 = 124 psi
Factory shows 9 - 13.5bar (approximately equal for all cylinders)
Thats 131 to 196 psi.
Any which way, I am low on pressure. Not sure what "approximately" means, but 15 psi seems 'reasonable' - except for all cylinders being low.

I put the boroscope down all 4 cylinders - no impressions, look surprisingly clean, but I swear on cylinder 2, I can see oil around the perimeter. Picture of the whole cylinder is #4- nice smooth cylinder walls, (all are like this) and you can clearly see the reflection of the piston. The closeup is cylinder 2, looks like something wet around the perimeter. Thought it might be gas, but blew it out with air ,and as hot as the engine is, I believe it is oil...

So I believe this is the answer - if the engine is beat up enough to have this low compression, its entirely likely that the bearings are shot. I also discovered it had 4 different spark plugs - fixing makes it idle a little better / maybe runs a little smoother, but its all relative. Stock plugs back in now.

Anyone agree / disagree?
I am attaching pics of the inside of cylinder 2

 

Sadly, you have found your answer. Good analysis.

 

for the record, according to bentley manual, max difference between all cylinders is 7psi.