Dennis or any other knowledgable guy

[PalmerWMD]

I sw this post of yours on a Z forum :

""Don't assume that the oil pressure gauge is very accurate without comparing it to a real external gauge where 1 psi increments can be read.

The only critical parameter is to not go below 14 psi IDLE [factory FSM spec] with the oil hottest [80 mph for 2-3 hours in 110F ambient].

Internal coolant temp gauges are purposely made inaccurate and heavily damped [slow to read changes once warm - overheat] to smooth the spikes.

An OBD2 scanner reads the real [what ecu works with] coolant temp within 1F...........watch the real temp vary 20F and the inside not move at all.

At higher mileage: One selects a summer oil viscosity and brand [Xw20, Xw30, Xw40, Xw50] that will not go below 14 psi [15-20][accurately measured] at hottest idle with the bearing wear you have!

Important to accurately check oil pressure every few years [30k] so you can graph the changes [bearing wear] to see when the engine needs retiring [200k, 250k, 300k].

I still exceed 14 psi [just 15-16 psi] with new HOT 10w30 Mobil 1 at 270,000 miles on my 15 year old Q45. Same as it measured with 200k in Summer 2000. Frequent oil changes with synthetic can prolong a good engine almost forever.......unless you overstress it [rod bolts]......we service one 94Q with 343,000 miles.............it only has about 12 psi of idle oil pressure but used conventional oil so you would expect a little more bearing wear.....even though it gets 8 oil changes per year.

The new 3.5 V6 is a total redesign so we will need to wait a few more years [a decade] to see if it is compariable.

Report post | IP: Logged You might find this discussion of Yamaha [SHO V6-V8] oil requirements interesting........discussed oil requirements in DOHC engines and bearing clearances.http://www.shoclub.com/lubrica...1.htm

G35 V6 = 0.0014-0.0018" main bearing oil film clearance --- wear limit 0.0026"1990-96 Q45= 0.0005-0.0012" --------wear limit 0.002"

As you can see from above the bearing clearances of the 3.5 are almost double the Q V8 but that was necessary to trade off lower friction [HP increase] for extreme longevity [still the wear limit of 3.5 is only 30% larger.

The 3.5 clearances would explain the need for higher oil pressure.

'''Does this mean we shuld consider running thicker oils on a VQ35de than Nissan suggests?They suggest the same oils listed for VH45de, 5w-30, 10w-30 and 10w-40.

But if the bearing clearances are so much larger than with the older engine (so much for the theory that thinner oils, are now recommended 'cuz engines are tighter, ), should we run thicker oils.

I am currently running M1 10w-30, which is a thinner 30 weight.

My VQ being so low mile and presumably tight, I figured it would be prudent vs the 0w-40, I would have used otherwise.

But perhaps I should go thicker sooner?OR does the different (ie higher pressure) oil pump in the VQ35de make this unnesseccary and pressures remain high to account for the bigger clearances despite the thinner oil?

Fred..

[s13sr20chris]

fred

i am not the knowledgable guy you are looking for but let me share my thoughts. the oil pump is regulated by spring pressure. i would think looser clearances would require more volume rather than more pressure. is this correct? also, how would the friction be lower in the 3.5? i would assume both engines are designed to achieve hydrodynamic film meaning either way they should have the same(relatively) low friction. eh?

[qship96]

"they list the same oils recommended for the vh45de-5w-30,10w-30,10w-40"

Fred,according to my factory service manual,and other infiniti documentation,10w-40,or any other 40w oil has NEVER been recommended for the vh45de-only 5w-30 0r 10w-30.

[PalmerWMD]

"they list the same oils recommended for the vh45de-5w-30,10w-30,10w-40"

Fred,according to my factory service manual,and other infiniti documentation,10w-40,or any other 40w oil has NEVER been recommended for the vh45de-only 5w-30 0r 10w-30.

What year is yours?In the manual for my 91 and my 94 recommends 10w-40 and 10w-30 in temps over 0F.5w-30 in lower temps.

Fred..