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Author Topic: oil Presure at Idle  (Read 1259 times)
jgilly40
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« on: April 04, 2011, 11:31:23 AM »

Hey Guys,

Im totally new to the Z world and have a oil preasure question. At idle my oil preasure gauge is reading extremely low. Once the motor gets a few revs it jumps back up to what I would call a normal level, around 50 psi, according to the gauge. This occures after the initial warm up of the car. Im really hoping that yall will tell me this is normal and i should quit wasting yall's time with stupid questions, but for curiousity sake: Should I be concerned?

1990 300zx twin turbo with 61,000 original miles on it. It doesnt smoke but i suspect it burns a little oil. I havent had the car long enough to know.

Thanks for your help
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iloveboost
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    « Reply #1 on: April 04, 2011, 12:29:27 PM »

    First of all, what do you mean by "extremely low"? There is a range of what the oil pressure of a TT should be according to your owners manual.  You will see the oil pressure goes down to around 20psi (at idle) according to the gauge and that should be considered normal.  Also, the stock pressure gauge isn't as accurate as you might think. 

    However, there is a chance that your oil pressure sending unit might be malfunctioning also.  It's located right above the oil filter.  I would replace it first, then check the pressure again.
    « Last Edit: April 04, 2011, 12:31:01 PM by iloveboost » Logged
    iloveboost
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      « Reply #2 on: April 04, 2011, 12:42:09 PM »

      Oops, forgot to mention that you can check the oil pressure sending unit by measuring the resistance across the 2 terminals.  The specs are listed in the service manual.
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      ManiacZX
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        « Reply #3 on: April 04, 2011, 02:19:54 PM »

        When I first bought my Z31 on the drive home I had a "freak out" moment when I got off of the freeway and was sitting at a red light, looked down and saw my oil pressure gauge sitting at 1 notch from the bottom.

        I was used to all my previous cars' gauges staying at the same levels once warmed up, not fluctuating like that.

        I quickly pulled over, cooled it down, checked the oil, sat there thinking "crap what do I do" heh.

        I started paging through the manual and found this:

        "The pressure is normal if the gauge remains within the range of from 2nd to 12th lights corresponding to the engine rpm"  (it says lights because I have a digital dash, on an analog it would be between the low and high range marks).

        So based on my experience with my Z31 and what Ed said, lower pressure on the gauge is fine at idle (just not too low, the needle shouldn't be sitting all the way at the bottom probably).

        Depending on ambient and engine temperatures and what weight oil your using, your pressure will be slightly different on throttle, but should be somewhere in the middle I would suspect.

        For example, my normal pressure moved up 1-2 notches when I moved from 20w40 to 20w50 last week.

        Z31s are the only sports car I've ever owned, but my assumption is this is one of the differences between owning a "sporty car" and a "sports car", your readouts are more informative because you are expected to be pushing the car in more extreme situations.
        « Last Edit: April 04, 2011, 02:22:30 PM by ManiacZX » Logged

        jgilly40
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        « Reply #4 on: April 04, 2011, 05:09:03 PM »

        first off, thank you for the responce.

        The gauge never actually reads zero. It hovers at around 8 to 10, but only at idle once it is warmed up. the preasue rises directly with the rpms. at normal crusing speed it holds very steady at around 50 psi. Ive read some other places and they too recomended changeing the sending unit. The car runs great. Im not extremely conserned but just wanted some confirmation.
        I have no idea what wieght or kind of oil is in it. i have only put about 300 miles on it so far. i m probly gonna go ahead and have it serviced soon though just so I can ease my mind further. It is not a dailly driver so I can let it sit for a while. I will probly go with a 5w-30 synthetic blend. Dont want to open a can of worms here but I dont like a full synthetic in an older motor. Ive tried it in two other cars and ended up replacing the motor shortly after both times. (Just personal experience, I sure others swear by them)

        I love the car and dont want to tear it up.
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        iloveboost
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          « Reply #5 on: April 04, 2011, 05:27:10 PM »

          It's great to see someone like yourself who takes the extra care of their cars!

          Both of my 91TT and 95TT hovers around the same range once it's in their normal operating temp.  I wouldn't be concerned about it at all, having the 120K maintenance done on the engine would be a much greater concerned though.  Unless you know the extended history of the car, I would definitely op for the 120K.  Snapping the Timing belt on this car will ruin your entire day quickly.
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          ManiacZX
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            « Reply #6 on: April 04, 2011, 06:17:11 PM »

            Running 5w30 seems very low especially heading into the summer.

            I pulled up a Z32 FSM and found this for the Viscosity guidelines.

            http://www.300zx-twinturbo.com/cgi-bin/manual.cgi?list=ma&dir=&config=&refresh=&direction=forward&scale=0&cycle=off&slide=11&design=default&total=33

            According to the chart, 5w30 is only good for up to 59F and in the footnotes says "5W-30 should only be used under extremely cold conditions".

            With heading into the Texas summer, I would think you'd want to do 20w40 or 20w50.

            On the synthetic, yeah, I stay out of debating that with others too.

            Your owner's manual should also have lubricant charts if you want to verify for your specific year, but that chart is probably accurate overall, it looks very similar to the recommendations for my Z31 too.

            Just remembered you said Louisiana in your profile, but I think it gets pretty darn hot there too right?
            « Last Edit: April 04, 2011, 06:24:30 PM by ManiacZX » Logged

            washingtond
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            « Reply #7 on: April 04, 2011, 06:51:51 PM »

            first off, thank you for the responce.

            The gauge never actually reads zero. It hovers at around 8 to 10, but only at idle once it is warmed up. the preasue rises directly with the rpms. at normal crusing speed it holds very steady at around 50 psi. Ive read some other places and they too recomended changeing the sending unit. The car runs great. Im not extremely conserned but just wanted some confirmation.
            I have no idea what wieght or kind of oil is in it. i have only put about 300 miles on it so far. i m probly gonna go ahead and have it serviced soon though just so I can ease my mind further. It is not a dailly driver so I can let it sit for a while. I will probly go with a 5w-30 synthetic blend. Dont want to open a can of worms here but I dont like a full synthetic in an older motor. Ive tried it in two other cars and ended up replacing the motor shortly after both times. (Just personal experience, I sure others swear by them)

            I love the car and dont want to tear it up.

            The gauge on my 1990 TT reads the same way and according to the owners manual that is within the normal range.
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            David
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            jgilly40
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            « Reply #8 on: April 04, 2011, 08:24:13 PM »

            Thank yall for the info. Ive learned alot today. It is nice to have a place to turn to for this kind of stuff. I sure hope yall dont charge for stupid questions. If so I'd better save up as I learn about my new toy. In the near future I will probly add an upgraded oil preasure gauge. Even if only to ease my mind.

            As far as Hot goes here in Shreveport we get the exact same weather as Dallas does. Only about 8 hours later. And for the record, the rest of the state of Louisianna doesnt really claim us in northwest LA. We are known as yankies. I usually just say that we are located east of Texas.
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            warrenkline
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            « Reply #9 on: April 04, 2011, 08:29:25 PM »

            I've done a lot of research on oils and had many samples tested by Blackstone labs. A proper (non race) street synthetic oil of the correct viscosity would never cause an engine to fail. Most exotics and high performance cars like Nissan's own GTR come with full synthetic oil. For many reasons the least of which is greater cooling efficiency then non synthetics.

            On the other hand if you have any Nissan other then a GTR a conventional oil changed with a filter on regular intervals will probably be more cost effective. Unless the price of gas goes much higher. Then a synthetic blend may pay for itself in fuel savings. - IMHO
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