Lowering oil pressure at hot idle

TimFZ

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?
 

jonbills

Membership Secretary
Site Administrator
Isn't 20/50 the oil recommended by Datsun?
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)
 

toopy

Club Member
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)

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

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

Farmer42

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.
 

ben240z

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
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
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


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

TimFZ

Club Member
Reporting back on this, 20w/50 did raise the oil pressure. I am now on classic sport Millers oil, semi synthetic with zddp. All good. But have some 20W60 for a good summer oil. That should keep it up!
 
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