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Old 10-18-2009, 04:47 PM   #1
ZR1Trev
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Oil pressure light flickers on at idle

I know this topic has been discussed before, but I have never seen a definitive solution.

Problem:
Red oil pressure light flickers on at idle, when engine is fully warmed up. This only happens when transmission is in Drive and car is stopped (idle speed 550 RPM). Light immediately goes out when brakes are released, car moves and idle speed increases. Light does not flicker when idling in Park (idle speed 650 RPM).

Background:
Car is an í03 325i with 70K miles (auto transmission). This problem has existed since I purchased the car 2 months ago. It has been serviced regularly at BMW dealers with oil change intervals in the 10K to 15K mile range. I recently replaced the valve cover gasket and VANOS seals. The valve train was perfectly clean with no sludge.

What I have tried:
Replaced oil and filter (BMW brand 5W-30 and OEM Mann filter)
Replaced oil pressure switch twice (FAE and BWD brand switches)
Cleaned Idle Control Valve and Throttle Body (trying to increase idle speed)

None of the above made any difference, so I decided that I needed to actually measure the oil pressure. I purchased a good quality mechanical oil pressure test gauge set with a 6 foot hose. It included 2 full sweep gauges, one with a pressure range of 0 to 50 psi (0 to 3.5 bar).

I removed the oil pressure switch and installed the hose and gauge. I ran the hose out under the hood near the driver side wiper and into the driver side window. This allowed me to monitor the pressure while I was driving. I made sure that the hose was not trapped by the closed hood (removed some of the under hood rubber seals).

I drove the car for 30 minutes to fully warm it up and then let it idle until it was hot and the auxiliary fan started to run. Here are the pressures that I measured:

RPM......psi......bar
550.......8.5......0.6....idle in Drive
650.......11.......0.75...idle in Park
800.......14.......1.0
1000......18.......1.2
1500......29.......2.0
2000......34.......2.3
2500......39.......2.7
3000......48.......3.3

I didnít test above 3000 RPM because I didnít want to exceed the 50 psi limit of the gauge.

The Bentley manual says the minimum pressure at idle should be 7 psi or 0.5 bar. So the pressure is within spec, but just barely at 550 RPM. This pressure must be low enough to activate the oil pressure switch even though it is not supposed to.

Has anyone else checked their hot oil pressure with an accurate gauge? I would like to know how these numbers compare. Is it normal for these engines to have fairly low oil pressure at hot idle?

My diagnosis is that my car probably has lower than average oil pressure (but still within spec) and a very low idle speed, which is making the problem worse. The idle is completely smooth and stable at 550 RPM in Drive.

Any ideas on why my idle speed is so low? Is it possible to increase the idle speed? (Bentley manual claims that it is not adjustable). Any comments or thoughts are welcome.

Thanks,

Trev
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Old 10-19-2009, 04:52 AM   #2
sprintman
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Use 0W40 as used in the rest of the world.
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Old 10-19-2009, 05:07 AM   #3
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Quote:
Originally Posted by sprintman View Post
Use 0W40 as used in the rest of the world.
That's probably not going to solve this person's car troubles. They have the problem even with the correct oil and maintenance, and they actually went through the trouble to verify oil pressure themselves and tried other options, More thought and effort than 95% of the members on here would ever do.

I have to commend this person for their efforts and hope they find a solution as this has not been an isolated issue.

But your comment, it just seems kinda rude and not very helpful considering their oil pressure seems to be just fine.

EDIT: 8.5 psi is normal according to bentley manual. 0w-40 has nothing to do with CAFE. Let's NOT turn this into an oil debate thread.
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Old 10-19-2009, 05:39 AM   #4
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8.5psi at idle??? Use 0W40 as the est of the world does. No CAFE in the rest of the world.
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Old 10-19-2009, 07:53 AM   #5
bmwbun
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Investigation done by the OP appears to indicate:

1) The oil pump is working OK
2) The pressure sending unit is not the problem.
3) The oil and filter is not the problem.

I agree with the focus of addressing the low idle speed.
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Old 10-19-2009, 09:11 AM   #6
BMWespresso
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Yeap the idle speed needs somehow to come up a bit, don't think 0w40 is going to help, and keep CAFE out of this
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Old 10-19-2009, 09:21 AM   #7
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Your idle speed is too low. Get it to 750 and you could be in business. Nope, 0w40 won't help. Even so, Australians do have some relevance to this problem. See this for kangaroos:

http://forum.e46fanatics.com/showthread.php?t=694567

Last edited by GoingNuts; 10-19-2009 at 09:27 AM.
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Old 10-19-2009, 02:26 PM   #8
SweetBMW
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this has also happened to me, i just started another thread.... but i put my car in the shop, and told them to swap the pressure sensor and the gasket between the oil filter housing and the engine block... but i told them to measure the oil pressure first..

im feeling this is gonna hurt my wallet.....
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Old 10-19-2009, 08:51 PM   #9
ZR1Trev
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Quote:
Originally Posted by SweetBMW View Post
... but i told them to measure the oil pressure first.......
Please report back when you have the oil pressure measurements. I'm interested to know if all M54 engines have relatively low oil pressure at hot idle. Note that the measurements have to be taken when the oil is very hot. Cold oil will produce much higher pressures. I was getting readings close to 50psi (3.4 bar) at a 700 RPM idle when the engine was first started in a 45 F (7 C) ambient temperature.
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Old 10-21-2009, 01:28 PM   #10
SweetBMW
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today igot my car back from the shop... they told me they checked the pressure, and replaced the pressure sensor and the gasket betwen the oil filter bousing and the engine block... and the light flickered again after the engine was warm.... so now i have put it back in the shop to say FIX IT

i fear i might have to replace the oil pumpl,sad tho, because the car has only 110k miles on it.. when do oil pumps usually fail?



edit: the car is not equipped with an M54 engine, its an M43TUB19
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Old 10-22-2009, 02:19 AM   #11
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I just got off the phone with the mech, and he told me he had seen something like this before, and that was a valve in the oil filter housing that was stuck... I have never heard of any valve in there, but hey what do I know? I just hope I can get this fixed as quickly as possible.. Anyone else figured out something new?
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Old 10-22-2009, 08:47 PM   #12
ZR1Trev
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Quote:
Originally Posted by SweetBMW View Post
... a valve in the oil filter housing that was stuck...
The only pressure valve that I know of is in the oil pump. Did the mechanic tell you what the oil pressure was when he checked it? Please let us know what the final solution is.
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Old 10-23-2009, 07:46 AM   #13
SweetBMW
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yeah thats what i thought as well, taht there was no valve in there.. but i just got pff the phone with them again, and now he told me he was just going for the test drive.. he had adjusted my idle (dont ask me how 'cause he wouldnt tell me) and that he was going to driveit for a while to check if the prioblem had gone away... but i was sure that the idle was not adjustable on this car, at least thats what AutoDATA tells me... but anyway if its fixed i will report back to you.. im not sure if i have a vacuum leak somewhere and that may be causing the low idle, causing the engine to struggle and maybe triggering the oil pressure sensor... well yeah.. anyway.. i'll chime in later this evening to see if its fixed

Cheers!


EDIT: No the mech did not tell me what the oil pressure was when he measured, just that it was within specs.. but as we know, within specs is a videly used term... for all i know it can be 6.1 psi and lets say the limit is 6.. you know? but i can always put on an oil pressure sensor myself and check it myself....
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Old 10-25-2009, 08:43 AM   #14
SweetBMW
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got the car back and now its fine... no flickering light, and still on 0w30 oil.... he has adjusted my idle apparently, dont ask me how as he still wouldnt tell me, but anyways, its all good now


idle is now around 700 ish in drive and 850 in N.. dont know if its a little high tho...


edit: im going to check the crankcase ventilation hoses and the valve to see if i might have any vacuum leaks that may have caused the low idle in the first place.... i'd consider checking this if i were you guys.. if your idle seems lower than it should be, check your hoses and the far back of the engine, from the valve cover leading to the intake...
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