I'll man up and admit it if I find that's the case.

 

have similar issue with a L83 chasing low oil pressure at hot idle problems . Any luck fixing yours ?

 

I can confirm I've fixed the low oil pressure problem. The issue was indeed the "upgraded oil bypass barbell" the one with the two o-rings. Do not use these. I replaced it with an OEM unit, the white nylon one, and it remedied the oil pressure issue immediately. Now I get a hot idle pressure of 29 psi, normal driving pressure of 40 psi, and over 3k rpm & 50% throttle 60 psi.

My theory remains the same, that by sealing off the bypass, the only pressure available in the oil gallery is pump pressure minus the pressure gradient of the oil filter material or 15psi whichever is less (because oil filters have a 15 psi delta bypass). There is one other theory, that the billet barbell actually has an o-ring that is too small which allows pressure to bleed off, where the bleed off pressure is a function of the oil viscosity/temperature. I only say this because it was rather easy to remove the billet barbell by hand and rather hard to tap the oem one in. A third theory is that the billet barbell is actually too short and has such a large shoulder that it impinges the flow through the oil gallery.

Anyways, I'm so glad to have things working properly now, and I can finally start breaking in the new engine. I hope this helps anyone in the future who is thinking about buying one of those billet oil bypass barbells, don't do it, save yourself a giant headache, just use the standard white nylon OEM one, it is the way it is for a reason.

 

I have one of those in my C5, which also has low OP.....

Almost no OP when hot. Hmm

 

I've never understood the obsession with replacing the barbell. I don't even think I've actually seen a failure from NOT replacing it.

 

I wouldn't call it an obsession. Its just that when you have a motor 100% torn apart and you're cleaning all the galleys and replacing every plug and gasket- why not "upgrade" while you're there

They do a good job of selling that barbell as an upgrade, and for $20 its one of those "this can't hurt" purchases

Turns out there might be 2 engines here where it in fact did hurt

 

'cause it's "billet"... LoL

Well OP, this is a good case study. I can't imagine any of your case scenarios causing low oil pressure, but my memory is kinda foggy on fluid mechanics... I'll have to brainstorm on why that barbell would cause low oil pressure.

 

Only way would be, if it wasn't exactly in that place between the 2 passages it's supposed to separate, between dirty and clean oil, but instead is hanging partway into one of them. Seems it would more likely be on the clean side since it's a bit shorter than stock.

 

Mine has a upgraded barbell but not sure which one it has though, there are several manufacturers it seems with several different designs. I have 45 to 50 psi of oil pressure at idle and over 60 at wot with the one I’m using.