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Oil pressure light after new HG

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    Oil pressure light after new HG

    So I changed out the head gasket, water pump, valve job, timing belt etc all the things you ought to do when you do a head gasket, including cleaning the old gasket material off the block (I had a machine shop take care of the head).

    I was worried about debris getting into my oil so i flushed the engine as best as I could while the head was off with some clean oil.

    Slapped the head back on with new head bolts to spec, put it all back together and she started right up, although a bit rough. I checked for vacuum leaks and i think i've got that sorted.

    But, my oil pressure light stays on after the engine is started. Its a 325iX so the steering rack is right in the way of the oil pressure switch. Which I didn't remove while i was taking off belts and what not. I'm using 20W30. I hear heavier oil might be better.

    How likely is it that the oil pump is clogged? :( Is there a better way to test the oil pressure switch with an ohm meter? I know its a 22 mm and it involves unbolting the engine mounts and loosening the sub frame. All of which seems pretty dangerous.

    #2
    Originally posted by RaabsIn513 View Post
    So I changed out the head gasket, water pump, valve job, timing belt etc all the things you ought to do when you do a head gasket, including cleaning the old gasket material off the block (I had a machine shop take care of the head).

    I was worried about debris getting into my oil so i flushed the engine as best as I could while the head was off with some clean oil.

    Slapped the head back on with new head bolts to spec, put it all back together and she started right up, although a bit rough. I checked for vacuum leaks and i think i've got that sorted.

    But, my oil pressure light stays on after the engine is started. Its a 325iX so the steering rack is right in the way of the oil pressure switch. Which I didn't remove while i was taking off belts and what not. I'm using 20W30. I hear heavier oil might be better.

    How likely is it that the oil pump is clogged? :( Is there a better way to test the oil pressure switch with an ohm meter? I know its a 22 mm and it involves unbolting the engine mounts and loosening the sub frame. All of which seems pretty dangerous.
    This info may help you, my understanding is there isn't an ohm test, as the pressure switch acts as, well, a switch. On or off.

    C101 Connector Pin#5 Oil Pressure Switch - Wire is connected to the oil pressure switch on the engine where it is grounded. The other end is attached directly to the clusters red oil pressure light. 12v is supplied to the light in the cluster, when the oil pressure dips below 0.4 bar the sensor grounds out, completing the circuit and turning on the light. From c101 it runs to pin 18 blue plug at the instrument cluster.

    That said, I'd attempt to unplug the connector at the pressure switch and see if the light is still on in the dash, if so the wire is shorted somewhere along the way to the c101 or between the c101 to the cluster, hence grounding and making the light come on.

    If you unplug and the light turns off, the pressure switch is definitely indicating a below .4 bar situation, or failed in a shorted way internally.

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      #3
      Try making oil pressure by runing the oil pump with an electric drill.
      You'll have to remove the airbox and the aluminum plug at the side of the block. Under that plug you'll find a little gear, when you remove that you'll see a shaft with a 6mm hex.

      With the help of a socket and some extensions you'll be able to rotate the pump. (Clock wise for the regular 325i, counter clockwise for the 325ix)

      I just did this recently when I had my car sitting for over 2 months. Took a little while turning it with a drill but you'll hear and feel the drill loosing power.

      That or you could remove the fuel pump relay and ignition coil and crank over the engine for a while..
      1990 325iX Touring - November 2018 R3V Car Of The Month

      1980 Volkswagen Golf mk1 1.1
      1974 BMW 2002 Touring

      Instagram

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        #4
        Thanks guys those are great things to look into.

        Is the hex head you speak of #27 in this exploded view? How does one take off the plug?

        https://www.realoem.com/bmw/enUS/sho...diagId=11_0117

        Comment


          #5
          Open the oil fill cap and make sure the oil spray bar wasn't left out during the head rebuild. If the bar is not there, oil is just spraying up under the valve cover. Only place I can think of where the head would effect oil pressure.
          john@m20guru.com
          Links:
          Transaction feedback: Here, here and here. Thanks :D

          Comment


            #6
            Originally posted by ForcedFirebird View Post
            Open the oil fill cap and make sure the oil spray bar wasn't left out during the head rebuild. If the bar is not there, oil is just spraying up under the valve cover. Only place I can think of where the head would effect oil pressure.
            Yessir, i did not forget to install the oil bar.

            Comment


              #7
              Did you damage the wires that go through the plastic ducts on the front of the upper timing cover ?
              89 E30 325is Lachs Silber - currently M20B31, M20B33 in the works, stroked to the hilt...

              new build thread http://www.r3vlimited.com/board/showthread.php?t=317505

              Comment


                #8
                Originally posted by RaabsIn513 View Post
                Thanks guys those are great things to look into.

                Is the hex head you speak of #27 in this exploded view? How does one take off the plug?

                https://www.realoem.com/bmw/enUS/sho...diagId=11_0117
                No, that's just the bolt.
                The shaft with the hex head is under that plug. I was able to pry it off with a flat screwdriver. Although I did struggle a bit it's doable in the confined space you have in there..
                1990 325iX Touring - November 2018 R3V Car Of The Month

                1980 Volkswagen Golf mk1 1.1
                1974 BMW 2002 Touring

                Instagram

                Comment


                  #9
                  Originally posted by digger View Post
                  Did you damage the wires that go through the plastic ducts on the front of the upper timing cover ?
                  It is certainly possible, I'll look for that tonight.

                  Comment


                    #10
                    Hey fellas, thanks again for all the replies. I finally had success!

                    It must have been a loose connector. After i fiddled with the two connectors in the oil pan (cleaned them out, made sure they were pushed in all the way) I got good oil pressure!

                    I'm not going to question it, the car gods smiled upon me i suppose.

                    I'm still a bit concerned about the head getting too hot for the short periods of time I've had the engine running. I installed a new thermostat, but its been so long. Is it even possible to install a thermostat in the wrong direction in these M20s?

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