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    oil fill cap leak

    My car weeps oil from the oil fill cap and seems to be seeping up from the plug wells on to the to of the vc..? I will try to post a pic. Symptoms are oil consumption (1qt every 1,500mi) tapping at cold start, intermediate tapping under load and low rpm, and Wet plugs. Before I just change the gasket , it sounds like I have a positive pressure problem pushing the oil, otherwise I can't see how I could have oil marks on top of the vc. Car runs smooth when warm except for the intermittent tapping described above. It does not smoke at start up, but under a hard pull I have noticed a small amount at night if someone is behind me with there headlights on. Can't see any at day time. Does this sound like worn ring blow by, or possibly a simple fix of some breather hoses/ valves? When I bought the car last year po had receipts with labor of all hoses replaced.

    #2
    It's likely that you have more than one issue to combat.

    First, if you're getting leakage from the valve cover/plug wells/oil cap you should start with replacing those. Remember that the plug wells have two types of gaskets and that the oil filter cap gasket can be replaced independently. Although getting a new cap is often economical.

    The tapping at cold start could be one of several things, the lifters or chain tensioner. If the lifters they're either dirty/worn (unlikely) or the oil is too light to make them happy. When/what was the oil last changed out with? If the tensioner it's a ~$40 part, but worth it if you hear a noise from the front of the engine. The tensioner is located above the A/C compressor under a 19 or 21mm plug.

    It's possible that you have an over pressure issue, but I'd be surprised as I've not heard of that in M42s before.

    To determine if your oil is leaking you'd need to do a leak down test and go from there. However, I'd be willing to bet that the stem seals are worn out, but that shouldn't eat 1qt/1,500mi. Any external oil leaks? Also check the intake tract to see if there's a load of oil in the intake boot which may indicate that your oil separator has given up.

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      #3
      It's the oil cap not the filter cap. I already changed the tensioner. Reason I'm thinking beyond just the gaskets it the leaking cap which is brand new. This makes me think it's getting a lot of positive pressure to do this. Also the fact that oil is depositing on the top of the vc above the coils like oil is misting out and settling there. Car has no other oil leaks, no marks on the ground, did the rear main when I did my clutch an fw and it was fine too. This car was originally a 91 325i, but two owners before me swapped in the m42. Based on other things done to the car they seemed to take care in maintenance and I have receipts for much of the repairs including a new used "good" head.

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        #4
        Trying to upload a pic
        Attached Files

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          #5
          So if you look at the top left of the vc you can see a bit of oil above the coil, along with a weep under the cap.

          It only consistently taps when it's cold, once it's warmed up I sometimes get little intermittent taps , for instance if I go up hill around 2500 to 3000 rpm similar to pinging. I not sure if it really is detonating because I've tried 100oct and it still will do that.

          Reason I'm curious these might be all tied together is I read a few other threads where they had the same issue and it contributed to being an issue with the cc vent valve , causing a lean detection in the dme which corrected and made the car run really rich. I don't see an air oil separator or vent valve on my motor. Just a vent hose that goes from the vc to the bottom of the tb.

          My car also does leave black debris on the garage floor behind the exhaust and has quite a bit of condensation to burn off on cold mornings. Ideas?

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            #6
            Originally posted by m42'd View Post
            It's the oil cap not the filter cap. I already changed the tensioner. Reason I'm thinking beyond just the gaskets it the leaking cap which is brand new. This makes me think it's getting a lot of positive pressure to do this. Also the fact that oil is depositing on the top of the vc above the coils like oil is misting out and settling there. Car has no other oil leaks, no marks on the ground, did the rear main when I did my clutch an fw and it was fine too. This car was originally a 91 325i, but two owners before me swapped in the m42. Based on other things done to the car they seemed to take care in maintenance and I have receipts for much of the repairs including a new used "good" head.
            I did mean to type filler, not filter. Assuming you checked, but is the gasket on the filler cap in good shape, does it click positively closed, have you adjusted the two locking tabs?

            Originally posted by m42'd View Post
            So if you look at the top left of the vc you can see a bit of oil above the coil, along with a weep under the cap.

            It only consistently taps when it's cold, once it's warmed up I sometimes get little intermittent taps , for instance if I go up hill around 2500 to 3000 rpm similar to pinging. I not sure if it really is detonating because I've tried 100oct and it still will do that.

            Reason I'm curious these might be all tied together is I read a few other threads where they had the same issue and it contributed to being an issue with the cc vent valve , causing a lean detection in the dme which corrected and made the car run really rich. I don't see an air oil separator or vent valve on my motor. Just a vent hose that goes from the vc to the bottom of the tb.

            My car also does leave black debris on the garage floor behind the exhaust and has quite a bit of condensation to burn off on cold mornings. Ideas?
            I do not see a good way, other than the oil cap, for oil to get on top of the VC without another oil leak present. However, I would encourage you to look again and see if oil could be leaking towards the fan and then getting distributed upwards. Are there oil deposits on the hood insulation or cover?

            Does your COP kit have the proper spacers to ensure that the middle two bolts on the VC are actually engaged and pushing the cover down?

            M42s only have an oil separator built in to the valve cover on the intake side. There's no PCV valve to contend with here. Condensation could be climate or a coolant leak in to a combustion chamber only when cold, which is unlikely. Again, a leak down test would be the only way to determine where you might have an oil leak in to the combustion chamber.

            As to the tapping, a video would yield a faster diagnosis.

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              #7
              I'm going to order a gasket kit and try to get a video of the tapping under normal operating temp. Once I take the vc off is it very hard to disassemble the lifters to clean them? Thanks for the response

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                #8
                It certainly won't hurt to replace the VC and plug well gaskets. However, M42 VC gaskets, but not the plug well gaskets, tend to last for a remarkably long time. When you do go to put the VC back on do be careful to not over tighten the bolts as they can be very easy to strip.

                Removing the lifters involves removing the cams/sprockets/tensioner/cam sensor (get a new o ring)/upper timing cover/thermostat housing (get a new thermostat housing gasket and thermostat o ring) but isn't anything too difficult if you're patient. Technically, you can remove the cam gears without removing the timing cover/thermostat, but you're much more likely to drop a bolt or have another first time issue. I've not disassembled a lifter myself, but I do believe there was a thread that covered it here or on M42Club some time ago. If you wanted to go all out, lifters are only $18 or less each brand new.

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