I've had an oil pressure gauge installed for a few months. It has been reading:

Idle: 27psi
Cruising (2.5k rpm): 35-40psi
WOT: 60-90psi


I just picked my car up from the dealer. Among the broken interior bits and rattles I had them fix, they found that the timing chain tensioner was leaking. So they fixed it.

Now the car is reading much different.
Idle: 27psi
Cruising (2.5k rpm): 70-80psi
3/4 Throttle: ~90psi
Haven't gone WOT yet.


So did fixing this little leak affect my oil pressure this much? There isn't really a way the dealer could have installed my sensor tap incorrectly. And what are normal pressures? '11 R56 S

 

Oil pressure can vary quite a bit from engine to engine. So if the engine is cold the pressure is much
higher than when it is warmed up. This is due to the oil being thicker. When warmed up, oil press
ure varies with RPM. At idle the pressure you should be in the 30PSI range. As the RPMs increase, so will pressure. But there is a factory release point around 90psi, which is reached around 4500 RPM.

 

I don't know about the MINIs, because we have electronic controls on our oil pressure system. But in old cars with purely mechanical oil pumps, the "rule of thumb" was that you wanted 10 PSI for every 1000 RPM. Less than that was Bad News, more than that was OK but could be a sign that your pump was larger than it needed to be. The oil pressure in those cars is directly related to RPM, because the pump was directly driven by the crankshaft or camshaft.

In those cars, the mechanical oil pressure relief valve would open at a given pressure, but the pump would keep pumping more as the engine RPMs increased. So the pressure would either stay steady after a certain point, or it would increase much more slowly with RPM after that point.

Oil pressure is also directly related to oil temperature. Cold oil will make higher pressure under the same circumstances than warm oil will.

 

So I guess they're normal numbers? The pressure range under throttle doesn't seem to change much between cold and warm. The idle does go down however as the oil warms up.

My main concern is why have my numbers changed so drastically after a trip to the dealer?

Is there anyone else around here with an oil pressure gauge on an N18 that could compare their numbers with mine?

 

Maybe having the leak was the cause of the low psi

 

Great notes... any updates?
One possibility.. a software update... the solenoid / oil pressure curve may have been updated.

 

Anyone happen to know at what pressure the low oil pressure light comes on?

I have an oil pressure gauge with an 'anunciator' that i can set to show a warning.

I wanna set it above that threshold.

My engine is new and i get 18-20psi at operating temp at idle with 0W oil provided by mini.

Thanks y'all.

 

If normal hot idle oil pressure is 18 to 20psi I'd set the warning threshold at say 15psi. In the case of low oil pressure the sooner you know the better off you are.

Have to mention though a low oil pressure condition if it occurs and this happens very seldom it is not likely to happen at idle.

If it does happen at all in some cases it happens under extreme usage -- read track usage -- under high g-force conditions such as can happen in a very sharp turn entered at the end of long fast straight which of course requires hard braking just prior to the turn -- which can have the oil level around the oil pump pickup low with the result the oil pump pickup ingests oil with some air still in it. The oil pressure drops but not enough to trigger the low oil pressure warning light.

Another scenario is at extreme high RPMs the oil level on the pan drops as a considerable amount of oil is suspended in the engine crankcase and under the valve cover. DOHC engines have a considerable amount of their oil budget expended on the DOHC oiling needs. Absent a good scavenge system this works to let the oil level in the pan drop. Even with no real g-force present the oil that is returned to the oil sump may not have lost its air and this oil gets picked up by the oil pump. The result in the hydraulic valve lash partially collapses -- because of air in the oil -- and this affects valve lift and timing. Engine output can fall off. (This has been observed on dyno pulls with the engine manifesting a severe drop off in power at near red line.)

In either of the above cases a low oil pressure warning system that is set to trigger at say 15psi is of no help.

To in some way help prevent the above it is important to run the right oil at the proper level and to not run the oil too long. Oil approaching its change by date is contaminated and this increases the amount of foaming/aeration the oil experiences. By having fresh oil in the engine the amount of foaming is reduced which can be the margin of safety.

 

Excellent points. Thanks for your thoughts. 15 PSI is what I have the alarm set at at now. We are in agreement.

My original engine had the low pressure warning light flash on a couple of occasions during hard turns. But it also suffered chronic oil leaks towards the end and then it blew valves in 3 cylinders at 150k miles. But I digress...

In this case its mostly my girl driving it and she drives very conservatively.

I'm just trying to get some warning via the alarm/annunciator before the low pressure warning light comes on since I know she isnt paying attention to the oil pressure gauge like I do. It's a long term play since this isnt going to be an issue now, on this new engine, but rather down the line when the inevitable leaks start.