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  • low oil pressure after driving

    my '85 turbo has good oil pressure after starting it, but when i start driving, the oil pressure falls off. what could cause this? is it just a bad sensor, or oil pump? i know its a basic question, i just want advise before i start blindly replacing parts.

    thanks!
    "Understeer is when you hit the wall with the front of the car. Oversteer is when you hit the wall with the rear of the car. Horsepower is how fast you hit the wall. Torque is how far you take the wall with you..."

    -'68 Datsun 1600 Roadster
    Build Thread: http://community.ratsun.net/topic/21...-build-thread/
    -'85 300zx Turbo
    Build Thread:
    http://z31performance.com/showthread...)build-thread!

  • #2
    the oil thins as it heats, if you use a low quality oil or run an oil too long the effect will be even more pronounced as the viscosity additives shear (break down). I like to use 15w40 diesel oil, especially in summer because it holds up much better than a conventional 10w40.

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    • #3
      My oil pressure on my 86T went all to hell when the seals on my trubo went bad. It started off with the pressure fluctuating a hare after hard driving with the occasional blue cloud out the exhaust. Then it stayed less than 15psi when it finally started smoking all the time.

      1986 300ZX Turbo...sold
      1990 Skyline GT-R...new money pit
      2014 Juke Nismo RS 6-speed...daily

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      • #4
        It could be a bad sender, you definately should find out for sure though before dismissing it... My old 85NA used to have perfect oil pressure at start up but if you stopped at traffic lights the needle would just go down to 0 if given enough time and it turned out to be the sender in that case. You need to make sure if it is or not though, does your oil light come on?
        http://youtube.com/c/zcartube

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        • #5
          You can get a mechanical oil pressure gauge from pep boys. That should give you an idea on whether or not the sender is bad.

          Try thicker oil too. Turbos get really hot and tend to shear the oil. I read somewhere (but don't quote me) that there were some z cars that cooked their oil in short order.

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          • #6
            Oil pressure sending unit, Nissan part#25070-21P00. They go bad from time to time.
            Matte Black 86T - Sold

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            • #7
              It is rare to find a Z31 with a working oil sending unit. The oiling system is rock solid, so unless you are losing oil, I would not worry about it.
              Chuck Stong
              300+ Parts and Performance owner
              http://www.300-plus.com
              2002 ZCOT president and always active member

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              • #8
                Firehawk wrote: It is rare to find a Z31 with a working oil sending unit. The oiling system is rock solid, so unless you are losing oil, I would not worry about it.
                That's been my motto. My gauge read Zilch when I got the car. I knew was just the gauge 'cause the car ran fine and didn't use a drop. Still doesn't. I replaced the sending unit but the gauge still sends out tarded signals. Just turning the key without starting makes the gauge jump to like sixty. It's random. I figure as long as the idiot light doesn't come on and i'm not using any, then i'm good to go. Nothing I can do about that anyway.
                My beloved Z:1987 2+2 NA2T w/30a swap.
                My black sheep: 88ss parts car (pretty much stripped and gone)
                207k miles and counting. Turbo'd since 155k.

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                • #9
                  the idiot light hasnt come on. and im running Mobil 1 synthetic 10w-30 with about 50 miles on the change. the oil shouldnt be a problem! i havent seen it leak, but ill check. and it has never hit 0 oil pressure, but hovers around 10-15 and wont go over 25 even at high rpm. also, my oil temp gauge doesnt read at all! grrrr.
                  "Understeer is when you hit the wall with the front of the car. Oversteer is when you hit the wall with the rear of the car. Horsepower is how fast you hit the wall. Torque is how far you take the wall with you..."

                  -'68 Datsun 1600 Roadster
                  Build Thread: http://community.ratsun.net/topic/21...-build-thread/
                  -'85 300zx Turbo
                  Build Thread:
                  http://z31performance.com/showthread...)build-thread!

                  Comment


                  • #10
                    I had a problem after a few months with my oil, engine started sounding like a diesel, oil pressure was pretty much at nothing so I did an oil change. It was pretty much empty lol, after I topped her back up she ran absolutely fine again, few months later it started again & I replaced the oil AGAIN not long after doing it the first time, car is running rich & burning oil, sometimes on gear changes I can see the puff of black smoke in my rear view mirror. At the moment it has no problem, soon as I start the car up the engine sounds fucked but as the car idles for a while oil pressure increases & the noise goes away & doesnt come back. Must take a while for the oil to circulate around. :roll:



                    1985' 2+2 Z31 Non Turbo...
                    1986' 2+2 Z31 Turbo...

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                    • #11
                      If your oil pressure sender is in good working order, and you are having lower oil pressure, definitely switch to a thicker oil.

                      I was using mobil 1 10w 30 when I did my turbo project, and I had ...decent pressure durring driving. But at idle, I would sometimes hit zero. And I knew it wasn't my gauge, because I replaced it.

                      Today I swapped to royal purple 20w 50 and its awesome! I have like 15 psi at idle, and all other recommended oil pressures to engine speeds are dead on if not a bit over.

                      Its a buck more than mobil one. I'm happy.

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