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  • Oil Pressure

    OK, when I picked the CJ7 up the dash wiring was a mess so over the last year I have been fixing things.

    The oil pressure gauge is bothering me. Either I have almost no pressure or there is still an issue with the gauge.

    At idle I get about 8PSI but once I rev up at all it drops to 0 or even below.

    The motor is not using any oil and runs great. I have run it on the highway for a few 2+ hour trips no issues no over heating no sized motor.

    The gauge seems easy enough. 3 Wired Red = hot, Black ground and Purple to the sensor.

    I have replaced the sensor and gauge but still no pressure.

    Is it possible that the hole into the motor where the sensor goes in is just blocked so I am not getting a good reading?

    OR am I about to blow a motor???

    Was wondering if removing the sensor and taking some high pressure air and blowing out the hole where it goes in might help. The jeep did sit for 3 years before i got it so may be gummed up bit still.

    Any ideas?

    I am planning an upgrade to a V6 since I currently have the 151 ci 4 banger in it but do not care for the idea of being stuck in the woods or along the road when the motor craps out if I really do have an oil issue.

    THanks

  • #2
    If you had an 'oil issue', the motor would have been toast on the first long trip. While the AMC motors are known for being all over the place on oil pressure, you still need more than 8 psi at idle.

    I'm betting either the sender is bad, or the guage itself.

    I would not blow compressed air into the hole where the sensor mounts, but removing and checking the sensor would be a good idea, if anything is plugged, it will most likely be the sender itself, becuase the inlet hole is very small.

    I didn't trust my guage, becuase the pressure was all over the place, so I went with a mechanical guage. It has an actual oil line that runs it, making it more reliable than an electric guage.

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    • #3
      Mine was a bad sending unit. Make sure the sending unit is grounded to the motor. No teflon tape thread sealer.

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      • #4
        I had problems with my oil pressure readings (high) and I found a Sunpro mechanical gauge at Advance store last month for about $8 on sale to confirm the readings.

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        • #5
          oil pressure

          Well I agree if I had no oil pressure the motor would have been toast a while ago.

          I installed a new sender and gauge, also checked the wires so I tink I am ok there unless the new sending unit was bad too.

          If I was to change to a mechanical gauge what would I need to order?

          Thanks

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          • #6
            It took three new sending units before I got a good one. First two made in china from auto-zone. Third one from carquest, american made.

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            • #7
              Originally posted by louism58 View Post
              Well I agree if I had no oil pressure the motor would have been toast a while ago.

              If I was to change to a mechanical gauge what would I need to order?

              Thanks
              You can get the complete mechanical guage, or a triple guage set(temp, oil, volts) at just about any parts store. The price varies from cheap to 'Are you nuts?' They come with everything needed to hook them up. I'm running both, the fatory and a triple guage mechanical set.

              http://ecx.images-amazon.com/images/...JL._SS500_.jpg


              Redtail has a good point, don't use teflon tape, the sender needs to ground. Theoretically, the brass fitting should seal without anything on it, but I've always used a little thread sealant.

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              • #8
                The port in the 4.2 head for the water temp sending unit is NOT large enough to install a mechanical gauge sending unit. FYI

                My 258 (11.5k on rebuild) runs a consistent 40-45 psi
                I know that the AMC motors are very sensitive to oil flow when they are fired up for the first time (after rebuild or brand new motor, or new oil pump). The oil pump MUST be primed via the distributer drive gear on the cam (with a drill) to prevent the oil pump from pumping air on the first start up.

                I dont know for sure, but I think that the oil pump not being primed may be partly to blame for 258s that have bad oil pressure. Just my theory...

                Ive heard of guys doing complete engine overhauls, and still having oil pressure problems afterward.

                Comment


                • #9
                  Originally posted by UPJ Wheeler View Post
                  The port in the 4.2 head for the water temp sending unit is NOT large enough to install a mechanical gauge sending unit. FYI

                  ............I dont know for sure, but I think that the oil pump not being primed may be partly to blame for 258s that have bad oil pressure. Just my theory...

                  Ive heard of guys doing complete engine overhauls, and still having oil pressure problems afterward.

                  Good points, I have my temp probe in the intake manifold water jacket.

                  I just fired up my fresh rebuild, and hav 60psi at idle, and 80psi at a slight rev. Much better than the 20-40psi I had before.

                  Priming is a good idea, but if the engine was rebuilt correctly, all wear parts will have been assembled with lube, made for the start up. If replacing an oil pump, or it's sat for a while, I would definately prime it.

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