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Thread: Too much of a good thing (oil pressure)

  1. #1
    Join Date
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    Too much of a good thing (oil pressure)

    As usual, no good deed goes unpunished. My 2002 started acting up today. Having completed my distributor rebuild, gotten everything running nicely, and washed the car, I decided to take it out for a proper shakedown. Nothing crazy, just a good long drive (~100 miles round-trip) to get things hot and loose for the first time in a while. Everything seemed fine except for the fact that for most of the drive my oil pressure was reading 2-3 bar too high (Mobil 1 15w50 and a Mahle filter, BTW). Normally it peaks about 4 bar at 4k RPM hot, and shows about 1 bar at hot idle; at the moment I'm getting 2 bar at idle and 6-8 bar at 4k RPM. Every once in a while it would drop down to its usual range, only to come back up again with revs.


    It's a VDO electric gauge, so naturally I figured it might be the gauge or the sender. Got home, engine still hot, popped the sender out, and screwed in my mechanical test gauge. Same readings. OK, so it's actually high. Pulled the cam chain tensioner out (this regulates the oil pressure). It came out freely and showed no signs of undue wear or dirt, and I could hear the ball shaking. I polished it anyway, blew out the small holes, cleaned up the hole in the chain cover, and slid it back in, making sure it engaged the chain (not spinning). Oil pressure still elevated.


    Pulled the valve cover off just to see how things looked. Seemed normal, oil evenly distributed around, nothing odd.


    So I'm running low on ideas here. Something is sticking, I suspect, but what? This engine has run the same oil pressures for decades and many thousands of miles. I mean, don't get me wrong, I'm happy the oil pressure went up instead of down, but I'd rather it just stayed where it's supposed to be. Thoughts?





    Life's tough. It's tougher when you're stupid.
    -John Wayne

  2. #2
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    You clearly know more about your engine than I do, so I have to ask fairly generic questions:

    Do you have a diagram of oil flow?

    Is your distributor work in any way involved in this circuit?

    I'm sure you've asked the latter question already, but a picture of the oil circuit might give a clue. After all, that lovely motor was built when there was still such data published.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  3. #3
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    Well, the distributor housing bolts to the back of the head. The oil pressure sender bolts to that, so it's definitely in the circuit. The trouble with this theory lies in the fact that I dip-tanked and then brushed clean the housing when I had it apart, and the oil galleries are simple and fully visible, so I know they are clean. I suppose it's possible something got dislodged and is blocking something, but it wasn't initially after I remounted the distributor a week or two ago.

    There's a pressure relief valve in the oil pump, but with fresh synthetic every spring and 3k miles tops per season, I think it's unlikely to have stuck. Everything I saw inside the motor today was as clean as its been for a lot of years now. Unless it's debris from the distributor swap, but I'm pretty careful about that sort of thing.





    Life's tough. It's tougher when you're stupid.
    -John Wayne

  4. #4
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    The oil pressure relief valve is probably sticking on the 320's the valve would stick and blow the oil filter seal. The relief valve valve is steel the oil pump body is aluminum different wear rates. Gets stuck.

  5. #5
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    A stuck relief valve is the worst case scenario. I really don't want to have to delve into that if I can avoid it.

    Perhaps this will offer some additional insight as to other possibilities:

    BMW M10 oil flow.jpg





    Life's tough. It's tougher when you're stupid.
    -John Wayne

  6. #6
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    hiss by my window
    Seems awfully coincidental to the distributor work. Don't overthink this.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  7. #7
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    Hmmm.....

    You know, my wonderful friend, that I fully recognize your dedication to the subject of oil. The proof is in the pudding, as the Brits say: You've got a six-million post oil thread, and you just provided the factory oil circuit diagrams.

    And, jeez....that distributor is indeed, right next to the oil pressure sensor. Is your gauge screwed into the stock hole?

    You saw it yourself, and noted the work you'd done. Ross mentions it too....and now that I see the diagrams, I have to say that there's something just too fishy about the proximity of one entity to the other.

    Hey, I've made more mistakes than you ever will. Tonight, I replaced an exploded radiator on my M5, used the opportunity to change oil/filter too. Changed the filter, vacuumed in the new coolant, filled with new oil.....oh crap. I now have 15 quarts of expensive oil in the sump. 7.5 quarts is dirty, 7.5 is new . Of course, I threw it all away. Sigh. Good news is, the car's just fine (I never started it). And, just to celebrate, we did 150 on the way home.

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  8. #8
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    I'm thinking the distributor is the most likely suspect for the obvious reasons, but at the same time I'm having trouble figuring out exactly how. Here's a shot of the distributor housing. As you see, the pressure sender is separate from the distributor oiling circuit. I'll pull the distributor and double check everything, but I can't figure out what in that fairly simple circuit could be causing such a dramatic change in pressures.

    I'm also going to check in with my indy here. He sold me my first 2002 and still has one himself, and he knows these motors inside and out. He may have an idea that's escaped me, or he may lend more weight to the relief valve in the pump being the cause. I'm also a little curious as to just how much of a concern he thinks it is.

    BMW 2002 distributor oil flow.jpg





    Life's tough. It's tougher when you're stupid.
    -John Wayne

  9. #9
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    150mph?! Chris, I know you’re a great driver and a great instructor (I have first hand experience). But, 150mph is a bit much. A tree could jump out in front of you!! Who’s going to re-teach me how to (properly) drive VIR???

  10. #10
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    Thinking out loud, I have never put a hand on that engine.
    I am picturing a bearing, similar to a cam bearing with an oiling hole, in the distributor. If this were the case and that bearing wasn't properly aligned that could be a restriction.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  11. #11
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    O2: While I understand the photo is maybe from a different engine than the one you just did the work on, maybe the gasket you used was missing a hole in a crucial spot? For instance, I'd guess there's been a hole blocked by the gasket in your picture, by the discolored spot on the lower left. I'm sure that's the way it's supposed to be, but maybe the new gasket was wrong? (Remind me to tell you about the Holley carb I rebuilt three times.)

    Chris Powell
    Racer and Instructor since, well. decades, ok?
    Master Auto Tech, owner of German Motors of Aberdeen
    BMWCCA 274412
    German Motors is hiring ! https://www.bimmerforums.com/forum/s...1#post30831471

  12. #12
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    Nope, it's correct - the housing is solid behind it. That's the end of the exhaust rocker; best I can determine, the oil from that gets funneled down through a smaller passage in the head to the distributor. I haven't had any time to look back into this, but as soon as I do I'll post an update.





    Life's tough. It's tougher when you're stupid.
    -John Wayne

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