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Discussion Starter · #1 ·
Hello everbody,
I have an issue on mini n12 2007 with low oil pressure. I checked all the possible blogs, threads, that exist on this issue with no positive outcome.
On cold start the oil pressure is 2,6 bars and gradually falls until it fully warms up, when it reaches about 0,3 bars and starts acting out.

What has been done so far:

-Head redone(grinding,checked valve seats and new valve seals)
  • new big end bearings
  • new chain set
  • OEM oil filter
  • new exhaust and intake sprockets
  • new oil seals on one of the camshaft(from metal to plastic)
-new oil pump new with chain and sprocket
- new exhaust and intake vanos actuator.

The only thing left that I know of is the oil filter housing. Yesterday it was removed and it seems fine, except that nobody knows if its OK that the spring inside has very low resistance( the one at the bottom of the housing, not near the filter). Should it be more sturdy?

Engine works flawless until it warms up.

I would appreciate anykind of help.


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4 Posts
Discussion Starter · #3 ·
If you have indicated low oil pressure both before and after you've changed the oil pump, I would question the gauge. When was the last time the gauge was calibrated or checked against a standard? Try another gauge.

Is the low oil pressure warning light on when you hit .3 bar?

.3 bar is 4.3 PSI, and the the idle spec for oil pressure on an N12 is .7 bar or 10 PSI.

What oil are you using?
Pressure is exactly the same before and after the swap of the pump. Gauge is new, also when the pressure gets too low, vanos starts acting up, random misfires etc. Also if I plug in pressure switch, the low pressure oil light will come on.

Current oil is 5w30, but considering to put in 10w60.

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Discussion Starter · #7 ·
Well, this is a weird one for sure!

Did you have the low-oil pressure problem before the rebuild?

Any exterior oil leakage?

Any evidence of oil in the coolant or coolant in the oil?

I think changing the weight to 10w60 will only mask the real issue.

So, let's think about how the oil system works. The pump sends oil up through the block to the oil filter manifold, through a check valve, and then through the filter. That oil flows to the main bearings and up through a passage in the block through non-return valve (another check valve) and on to the VANOS solenoids, timing chain tensioner, and the moving pars of the cylinder head, tappets, camshaft bearings etc. The oil pressure switch is in the upper end (end of the line) in the cylinder head. So, any restriction in the system could cause the pressure to rise (before the restriction), and drop (after the restriction). Your above idle pressure seems low too. After I changed my oil pump, I check the pressure, and I had 48 PSI above idle. 2.6 bar is 37.7 PSI.

I'd pull the non-return valve (connect a hose to the port), disable the ignition and fuel system, and crank the motor. This would be to flush any contamination from that passage. Then I'd put in a new non-return valve. If the non-return check valve isn't opening when the oil pressure hits it, you would have reduced oil pressure to the VANOS solenoids, timing chain tensioner, cylinder head components and the low-pressure switch. Recheck your idle pressure after you change the non-return valve. If it's still low, I'd look to the the check valve in the oil filter housing. However, the check valve in the oil filter housing is a bypass type. It only opens if the oil filter is clogged, allowing oil to flow in case of excessive filter contamination.

View attachment 281291

Oh! And I know this is the obvious point, but what is your oil level on the dipstick. Not to be insulting of course.
Yes, issue was there before the rebuild. There is no exterior leakage whats so ever and no signs of coolant in oil and/or oil in coolant.

The non return valve canal should be clean, since whole head was cleaned. However I did order a new valve today just to make sure.

Do you have more info about oil filter housing? This is the type that its installed:

And this is the installed filter:

And yes, I checked oil level on multiple ocassions😁, even bought an oil dipstick on which oil level can be seen more easily.

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Discussion Starter · #10 ·
No the big ends are the conrod bearings, the mains are the crankshaft to block bearings.

Gerry View attachment 281299
Sorry i missed your reply. To my knowledge big end bearings are usually the first one to go. Since the big end bearings were not in bad shape at all-no damage, no scorching etc.(we swaped them because to try to solve this issue), we didnt even check the mains in this case. Correct me if im wrong tho 🤔
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