Lowering oil pressure at hot idle | The Z Club of Great Britain
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Lowering oil pressure at hot idle

Discussion in 'Engine' started by TimFZ, Jun 9, 2021.

  1. TimFZ

    TimFZ
    Z Club Member

    Had a great drive in my S30 this week but in the hot weather and after a longer faster drive I noticed the oil pressure drops a lot at idle when hot. Its fine when cold and in both cases increases as revs go up somewhat.

    I put in 15W40 Millers classic oil. Would you guys recommend a thicker oil to maintain pressure? 20W50 may be better in the summer. Any thoughts?
     
  2. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    I'd use 20/50 but low pressure at idle is common for these engines.
     
    TimFZ likes this.
  3. Bazzateer

    Bazzateer
    Z Club Member

    Isn't 20/50 the oil recommended by Datsun?
     
  4. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    They also recommended points in distributors until technology moved on.
    20/50 is always mineral oil isn't it?
    full synthetic oil is much better than mineral.
    5/40 is good.
    (but add zddp)
     
  5. toopy

    toopy
    Z Club Member

    This from the Millers website for the 20/50 Classic Sport, i think the non-sport version is mineral or maybe semi synthetic.

    This high performance oil is the world’s finest SAE 20w50 fully synthetic multigrade engine oil. It has been uniquely engineered for classic performance racing, with shear stable viscosity index improvers. This product incorporates our unique nanotechnology ultra low friction additive system. It is formulated with full ZDDP (zinc phosphorus) for ultimate protection.
     
    jonbills likes this.
  6. jonbills

    jonbills
    ZClub Administrator
    Staff Member Moderator

    Thanks, can't argue with that, although the "20" bit will mean you have to warm it up very thoroughly before any beans.
     
  7. TimFZ

    TimFZ
    Z Club Member

    I don't really give it the beans anyway. Its a classic to preserve not take on the track!
     
  8. Farmer42

    Farmer42
    Z Club Member

    If you are getting pressure drop on high temps then I would also advise replacing the sender. They do clog over time and give false readings.
     
  9. ben240z

    ben240z
    Z Club Member

    10 psi/1000rpm is what I have always worked to with a hot engine. Therefore 10psi at idle would not worry me

    Having used it for some years now I would really consider fully synthetic oil.

    Just my opinion
     
    jonbills likes this.
  10. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator


    Hi Ben, but your car never does more than 2 miles at a time. ;)
     
    TimFZ likes this.

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