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Discussion Starter #1
1992
525i
256,xxx
5 speed Manuel

I've been currently using 20w-50 Castrol high mileage oil... at one point I was running low on oil and seem like it was running good! Smooth idle after I topped it off it started running rough again.. the car drives fine however I can tell is has a rough idle is Bc of my loud Magna flow changed tone for a few seconds also if I sit in my car I could feel the slightly but noticeable rough idle... should I get thinner oil?
 

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If you changed nothing about the oil weight from when it was running smoothly, why would you assume it is directly related to a poor running condition now? Depending on how low you let the oil get, that alone could cause quite a few issues. IMO though, jumping to such a conclusion would be a bit premature at this point.
 

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5,550 Posts
1992
525i
256,xxx
5 speed Manuel

I've been currently using 20w-50 Castrol high mileage oil... at one point I was running low on oil and seem like it was running good! Smooth idle after I topped it off it started running rough again.. the car drives fine however I can tell is has a rough idle is Bc of my loud Magna flow changed tone for a few seconds also if I sit in my car I could feel the slightly but noticeable rough idle... should I get thinner oil?
thick oil can't lubricate lifters after start up. do you have a massive lifter ticking at the beginning?
 

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Discussion Starter #4
If you changed nothing about the oil weight from when it was running smoothly, why would you assume it is directly related to a poor running condition now? Depending on how low you let the oil get, that alone could cause quite a few issues. IMO though, jumping to such a conclusion would be a bit premature at this point.
It never did run smoothly I always thought it was a vacuum leak or my exhaust
 

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thick oil can't lubricate lifters after start up. do you have a massive lifter ticking at the beginning?
Yes. But the noise comes from under the front bumper and the bumper seems to be tight and not cracked or loose so I know it's not the bumper
 

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I'd agree, the thicker the oil, the more it can screw around with feeding the hydraulic lifters, but as it warms up it ought to smooth out. Experience with that subject had me "warming" my car up until pretty flipping much operating temp. In any case, I ran 20w-50 for years, and given >250k on O.P's engine, I wouldn't be concerned with that weight. Damn I wish these cars had oil pressure gauges stock... One thing to note though, if you ran it really low, it's possible that it pumped some air bubbles into your lifters. If that were the case, the result would be very irregular idle (car and engine noticeably vibrating), and probably a loss of power to a small degree. If that's what it is, make sure your oil stays full, and get the RPM's up (~3,000 or a smidge higher) for a few 5-10 mile drives. That would likely evacuate the trapped air within the lifters.

Whatever is happening, did I miss something? You've been using the same oil weight, or you just tried it, ran it low at the same time, and now you have seemingly tied together assumptions?
 

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1992
525i
256,xxx
5 speed Manuel

I've been currently using 20w-50 Castrol high mileage oil... at one point I was running low on oil and seem like it was running good! Smooth idle after I topped it off it started running rough again.. the car drives fine however I can tell is has a rough idle is Bc of my loud Magna flow changed tone for a few seconds also if I sit in my car I could feel the slightly but noticeable rough idle... should I get thinner oil?
when was it running smooth? while filling the oil and the cap was off? Or for a longer time after.
 

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Discussion Starter #8
I'd agree, the thicker the oil, the more it can screw around with feeding the hydraulic lifters, but as it warms up it ought to smooth out. Experience with that subject had me "warming" my car up until pretty flipping much operating temp. In any case, I ran 20w-50 for years, and given >250k on O.P's engine, I wouldn't be concerned with that weight. Damn I wish these cars had oil pressure gauges stock... One thing to note though, if you ran it really low, it's possible that it pumped some air bubbles into your lifters. If that were the case, the result would be very irregular idle (car and engine noticeably vibrating), and probably a loss of power to a small degree. If that's what it is, make sure your oil stays full, and get the RPM's up (~3,000 or a smidge higher) for a few 5-10 mile drives. That would likely evacuate the trapped air within the lifters.

Whatever is happening, did I miss something? You've been using the same oil weight, or you just tried it, ran it low at the same time, and now you have seemingly tied together assumptions?
I drive 60 mile round trip everyday on around 3,000 RPMs so I'm sure the problem would of went away a long time ago... but I'll definitely give it a try and let you know!
And this (slightly noticeable) rough idle has been going on forever I just thought it was a vac leak. but last week before I put this thread up the car was three or four courts low on oil and had a vary smooth idle until I toped it off. Sometimes but rarely I could feel and hear the car bog down for a sec like it's about to die then come back to normal but still have that slightly rough idle.
 

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Discussion Starter #10
Also I've been using this wight since I've bought it.. and the previous owner said he's been using the same oil since 94
 

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I really have a hard time believing the oil weight has anything to do with your issue. Over-fill, maybe, but the strangest part to me, it getting down 4 quarts. Where did they go? Leaks? Other fluids (coolant, trans) look fine? Spark plugs show signs of burning it?
 

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Ccv

It was running smooth when it was three courts of oil low.. after topping it off it started idling rough again
I have heard of some CCV's leaking oil into the intake manifold, don't know much about it, but if true, it could cause rough idle when oil is toped off, and explain how you could use 3 or 4 quarts of oil and be that low JAT
 

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Discussion Starter #13
I really have a hard time believing the oil weight has anything to do with your issue. Over-fill, maybe, but the strangest part to me, it getting down 4 quarts. Where did they go? Leaks? Other fluids (coolant, trans) look fine? Spark plugs show signs of burning it?
Sorry I should have said this when I made this thread.. I had a bad valve cover gasket and so I replaced it last week
 

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Discussion Starter #14
I have heard of some CCV's leaking oil into the intake manifold, don't know much about it, but if true, it could cause rough idle when oil is toped off, and explain how you could use 3 or 4 quarts of oil and be that low JAT
Yes I took my manifold off five month ago and there was a decent amount of oil in it also the air intake boot (I did clean it)
 

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Discussion Starter #15
Know there is also this ticking noise coming from underneath my car I want to say it's coming from my exhaust.. I could have a exhaust leak but could it really cause my engine to have a slightly rough idle like that?
 

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I think 504 is possibly onto something with regard to the CCV system. I can make sense of full oil=more getting into the intake. A popped diaphragm in the rear plate could be making all kinds of a mess for you, and that's not even considering how clogged up the oil separator likely has gotten. I had direct experience with this. Let go long enough and it will cake up the backside of your valves, and can gum up both the injectors and spark plugs. Not to mention what it does to the combustion chamber.

When I rebuilt, I put that cyclonic oil separator in Chem-dip for weeks before it broke all the crud down in it. Having the time I had, meant I didn't need to replace it. I'll keep it short on this, because it's flipping buried in there, and cleaning it in place would be nothing short of guess work.

Whatever you do, if you've got a bunch of oil standing in the intake manifold, and your runners into the heads are caked up, you're gonna want to address it. Not gonna get better, and I'm sure I don't have to say, running it low on oil so it runs better for now, isn't really a solution eh.. :)

What is your manifold vacuum pressure? If you don't have a tool, this is what I use: http://www.harborfreight.com/fuel-pump-and-vacuum-tester-62637.html
 

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Discussion Starter #18
I think 504 is possibly onto something with regard to the CCV system. I can make sense of full oil=more getting into the intake. A popped diaphragm in the rear plate could be making all kinds of a mess for you, and that's not even considering how clogged up the oil separator likely has gotten. I had direct experience with this. Let go long enough and it will cake up the backside of your valves, and can gum up both the injectors and spark plugs. Not to mention what it does to the combustion chamber.

When I rebuilt, I put that cyclonic oil separator in Chem-dip for weeks before it broke all the crud down in it. Having the time I had, meant I didn't need to replace it. I'll keep it short on this, because it's flipping buried in there, and cleaning it in place would be nothing short of guess work.

Whatever you do, if you've got a bunch of oil standing in the intake manifold, and your runners into the heads are caked up, you're gonna want to address it. Not gonna get better, and I'm sure I don't have to say, running it low on oil so it runs better for now, isn't really a solution eh.. :)

What is your manifold vacuum pressure? If you don't have a tool, this is what I use: http://www.harborfreight.com/fuel-pump-and-vacuum-tester-62637.html
I didn't fix my problem I just cleaned out the boot and the manifold. How ever I have a 92 m50 non vanos I don't think it has a diaphragm, I don't remember seeing a diaphragm when I was taking my manifold off? Also there is a hissing sound coming from right under the manifold and I'm assuming I have a small vacc leak or a vacuum hoes disconnected.
 

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Ccv

Not knowing your motor that well, you may not have a CCV, but must have some kind of PVC controlling blow by in your motor. If you have had that kind of oil in your manifold it is coming from the crankcase somehow, so I would still, find / fix it. As to your rough idle, if you hear a vacuum leak, fix that before you do anymore trouble shouting IMO.
 

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Discussion Starter #20
Not knowing your motor that well, you may not have a CCV, but must have some kind of PVC controlling blow by in your motor. If you have had that kind of oil in your manifold it is coming from the crankcase somehow, so I would still, find / fix it. As to your rough idle, if you hear a vacuum leak, fix that before you do anymore trouble shouting IMO.
Yes I'm going to be ordering a new PCV valve.. mine is loose and it's seeping out oil
 
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