When to worry about engine noises?
I have a new standard volume pump with a high pressure spring in my slant 6 and it's rock steady at 70PSI at hot idle. It rises to about 75 "or so" PSI with RPM, but that's about all it gets because the relief valve starts working.
It funny you mention this because
@lead69 and I have been going down the rabbit hole on this for some time now.
Pressure is the measurement of restriction to flow (I know YOU know this, I just want to set the ground work so it makes sense to some who may not know) so either the more oil you try and push through a restriction or the higher the viscosity of an oil you push through the same restriction(s) affects what we see on the gauge.
The problem is (one problem anyway) that an oils viscosity is based on its grade (not “weight” as there is no such thing as a “weight” of oil) and it’s temperature. Change one or both of those and you change what’s seen on the gauge.
The last part of that is the cumulative effect of all the leaks in the system. These include all the leaks at all the bearings, the leaks at the rockers, the lifters.
If you increase the clearance you reduce the pressure because the leakage is higher. You can reduce the clearances (or make a repair if say a lifter bore is loose or something) or run a higher grade (less viscous) oil. That will increase the pressure.
What used to be the norm was all these aftermarket cranks were coming ground on the mid to high side of the tolerance. Sometime, even if you opened up the rod and main bores to the maximum you’d still be tight. Plus you’d have the minimum bearing crush.
Thats what .001 and .011 bearings for Chevys were available. Thats why most of the stuff I did back then got chevy rods. And yes, I turned brand new cranks down to Chevy rod throws and .010 mains so I could run the bearing bores at the minimum and still get the clearance I wanted.
Today, that appears to NOT be the case. It’s looking like they are now grinding the cranks to .001-.0015 UNDER minimum!!!
So even with the housing bores at the minimum, you still can get well over .0030 clearance. IMO that’s way too much for todays oils.
The rule of thumb has been .0010 clearance per inch of shaft. Today, most stuff can be .0095 or even a bit less. That means for a 2.125 shaft you can be at .0020 clearance. My mains (340 size) are set up at .0023 so that’s about .0093ish per inch of shaft diameter.
That means I can run a 0W20 oil and still have enough pressure (and flow) to cool and lubricate the engine. And it will most likely cool and lubricate better with the lower grade oil because it flows much faster and shed heat a bit better than a heavier grade oil.
Certainly that will make more power as well.
I said all that to say that when you see low oil pressure it’s probably a combination of things. More clearance that is needed, a lower grade oil than needed or both.
I‘m from the end of the era when running a 50 or 60 grade oil and .0029-.0031 on the rods and .0038-.0040 on the mains was standard.
One of the things I miss most is paper carton oil cans and the push in oil spout.
With the oil we have today we can tighten down the clearances, run a lower grade oil, make more power and have the engine live longer.
If the clearances are still from the 1970’s then you still need to open the clearance up.
