epix

iTrader: (2)

Had an engine built for my Trailblazer that consisted of a L92 block from an Escalade. It has a forged rotating stroker assembly bringing it out to a 416. Used a new Trickflow 230/238 cam and cnc ls3 heads with aftermarket components.

Oil pump is a Melling HP 10355 pump. I replaced the oil pressure sensor and also attached an aftermarket oil pressure gauge. Oil used after break in has always been a quality 20w-50.

Engine was put in about a year and half ago with about 6000 miles on it now and runs fine with no odd noises, but it has always had an issue with oil pressure seeming low. At start up oil pressure will be around 35-40psi but once warm and at idle or when I deaccelerate quickly the oil pressure drops. When engine has ran for 20+ minutes the oil pressure often will only be around 6-10psi. Raising the RPM's brings the oil pressure up at about 10-12psi per 1000 rpm, but soon as you idle it goes back down and will even trip the low oil pressure warning on my dash.

Likely it is bearings? I did have an aftermarket oil pickup tube installed as the AWD TBSS stock pickup is a bad design that leads to oil starvation.. there have been reports of the o-ring getting pinched.. not sure what the symptoms of that would be.

I want to get to the root cause of this before I really have to replace expensive components!


edit: Each time I change the oil (about every 2000 miles) I have never seen gold specs in the oil nor bits of metal.

G Atsma

Look for tiny bubbles on the dipstick while running. That would indicate air being sucked into the oil pickup tube past the pinched o-ring

epix

iTrader: (2)

I'll be most likely removing the engine in the near future. After speaking with others I've been told with a compromised o-ring the oil pressure would be low even at start up.

I have noticed it is dripping a small amount of oil each time I drive it. After parking it after a drive I set a container under where I saw a drip. Only about 3-4 tablespoons worth. Unsure of the the source of the leak at the moment. Oil looks clean.

Sounds like chances are the bearings used were too lose for this build. Hopefully I can get away with a rebuild just using fresh correct size bearings with no/minimal machine work.

A.R. Shale Targa

iTrader: (2)

sounds just like the main clearances were set up for an iron block application
The aluminum blocks grow so much that the clearances open up and bleed off
oil pressure.
Mine were about a half thousandths (.0005") larger than I had planned for
using .001" under main bearings on a polished 100,000 mile LQ4 crank
Ultimately you will want to be in the (.0015"-.0018") range at room temp since they end up closer to .003" at operating temp.

epix

iTrader: (2)

You're probably right, talked to others and they agree about bearings.

When I went over the build sheet "X" Clevite bearings (MS-2199HXK) were used which are 0.001" OVERsized.

We'll be pulling the engine in a week or two and hopefully get away with simply replacing the mains if no damage has been done already. Until then I'm keeping vehicle parked.

JimsNovaLS

My last two aluminum LS builds I mixed .001 under mains in the block and standards in the caps to achieve my desired clearances of .0017 to .0019.

Before you tear into the bottom end, check the valley cover bolts for required torque. I saw this once where the valley cover bolts were snugged but never torqued and the oil pressure did just what you're seeing and it only leaked a little oil down the back of the engine. The oil was pushing past the DOD tower seals back to the crankcase. It's easy to check.

tech@WS6store

iTrader: (2)

Why use such heavy oil and high volume pump?

01CamaroSSTx

iTrader: (3)

I second that! Throwing thicker oil into an engine clearance'd for a 5w30 is merely causing more of an oil restriction isn't it?

I'm running 5w30 through my LSX427 which has a high volume oil pump. I was having similar problems as you described and determined that the pick up tube was too close to the bottom of the pan causing an oil restriction. The 4th gen pan was replaced with a Moroso 6 qt set up and an oil filter relocation kit. Now it idles at operating temp around 50 psi and 60 psi when I mash the loud pedal!

01CamaroSSTx

iTrader: (3)

Here's some pics of the Moroso 4th gen oil pan and the relocation kit.