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    No Oil Pressure

    Good evening,
    I have made the anual oil change and took the opportunity to sort a leakage at the oil pump. All three o-rings have been changed. Everything is installed now and when I turned the engine without ignition in order to fill everything with oil and build up oil pressure the gauge needle remained at zero. I opened the pump relief valve in situ in order to check whether I made a mistake during reassembling. No, everything is ok. I srewed the spin on oil filter off and (appr. cup full of) oil came out of the oil ways/gallery. So the pump does feed but with or without pressure.?

    My questions:
    --is there really no oil pressure or is the pressure gauge/pressure sensor faulty?
    --how can I check the two VDO units? When I started the winter brake for the Stag 6 weeks ago I didn't watch the pressure gauge so I don't know whether it was indicating pressure or not.

    Here is the VDO wiring diagram:
    -any further ideas and help are highly appreciated.

    Klaus
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    Last edited by Klaus Schlueter; 15 November 2018, 19:55.

    #2
    Do you still have an oil pressure light, and if so does it go out when you crank the engine? If the light does go out it suggests a fault with the gauge or sensor.

    It is normally possible to hear the speed the engine the engine is cranking reduce as the oil pressure comes up and puts extra load on the starter motor.

    Neil
    Neil
    TV8, efi, fast road cams and home built manifolds. 246bhp 220lbft torque

    Comment


      #3
      Many thanks Neil, do you means the oil pressure light in the multi cluster? If so I can check that tomorrow as the pump relif valve is still open. I hope I can get the spring and plug back in in situ.
      Klaus

      Comment


        #4
        Yes I do mean the one in the cluster. Does it still have its original pressure switch, or does it rely on the one for the gauge?

        I find the oil pressure switches to be somewhat temperamental, at least some new ones are, but when they do fail they normally fail with the bulb not lighting
        Neil
        TV8, efi, fast road cams and home built manifolds. 246bhp 220lbft torque

        Comment


          #5
          It is still the original one. The pressure gauge is separate from VDO with a warning contact.

          Comment


            #6
            You could take out the dissy and drive the hex drive to the oil pump with a drill or spin it with a handle on a socket and extension. I find you can feel when there is pressure and you can also hear the oil circulating.
            anti clock of course.

            Comment


              #7
              Yes, I'll try that tomorrow

              Comment


                #8
                If you took the pump apart, and put it back dry, it may be that it hasn't "primed" itself yet.

                When I did mine I filled the pump itself with oil before I refitted it to give it a head start.

                In your case I would try the drill method as Stagdad suggests, eventually it should build pressure.
                Header tanks - you can't beat a bit of bling.

                Comment


                  #9
                  Yes I took it apart and checked the dimensions. Still perfect after 25 years and 190 k km (Saab pump). I lubricated it but I didn't fill it with oil. I'll surely try the drill method if the electric check fails.
                  Klaus

                  Comment


                    #10
                    Klaus,

                    do you need a hex drive to spin the oil pump (counter-clockwise!)?

                    I'm in Gernlinden at the weekend and have already popped it into the boot of the car for you in case.

                    To prime the pump I used an assembly grease from moly. It's designed to 'dissolve' into engine oil following start-up - I might have a bit left in the tube.

                    Drew
                    The answer isn't 42, it's 1/137

                    Comment


                      #11
                      Many thanks Drew. I have found the required parts in my toolbox.
                      A short update. The dissy is out and I'm about to manually spin the oil pump. The pump does feed, I could hear the oil when filling all the cavities and the filter. And when everything is filled I feel a pressure build up and the lever of my spin unit turns backwards. I have checked the pressure gauge and yes there is pressure in the system. But is it normal that the pump wants to spin backwards? Is there something blocked in the system?
                      Klaus
                      Last edited by Klaus Schlueter; 16 November 2018, 20:43.

                      Comment


                        #12
                        Am I correct that there shouldn't be a pressure build up when spinning the pump manually with only appr. 30 RPM? And if l use a drilling machine with let's say 800 RPM l should read idle oil pressure of appr. 1 to1,5 bar?
                        Klaus

                        Comment


                          #13
                          30 rpm is a bit too slow to build oil pressure IMHO, I remember nearly burning out a drill the last time I primed a yank V8 with it, that was at much higher speed. More like 500rpm, when I saw 50 to 60 psi on the gauge. very different engine though.

                          If it is building enough pressure to show 20psi or more on the gauge with a drill, I think you are good to go.
                          Header tanks - you can't beat a bit of bling.

                          Comment


                            #14
                            Everything back together now. It took a while as the weekend was full of other work (garden).
                            To be honest, I couldn't find anything wrong with the pump and the spin-on filter system. I took all apart again-no fault visible. As the oil pressure light in the cluster and the VDO pressure gauge both didn't work at the beginning I speculate that there was a hidden electrical fault.
                            Yesterday I made a 15 km test drive (blue sky, +3 C, top down ) and all looked normal with 4 bar oil pressure (today we unfotunately have the first snow in Munich with -5 C).
                            So again thank you very much for all your input, that was very helpful for me.

                            Klaus

                            Comment

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