Kubs

Last fall I developed a low oil pressure issue on my new engine. The car started to idle at <10psi. It had good pressure when I built it (30-35psi at idle) and increased with RPM like normal. The low idle press happened after 6 laps of evaluation in track. I did not push it hard, just kind of drove around and came back to the pits. The few points I checked the pressure on track it was around 40-60psi. When the engine cooled a little bit idle pressure was around 20psi, but did not climb very much with RPM. I figured I would start with the easy stuff and tired 50wt (it had 30wt in it before) oil to see what would happen. Cold idle was now 10psi, but started rising slowly as the car idled for several seconds. I decided to pull the pan and check out the oil pump. I was epecting to see a broken or weak pressure spring. I took it apart and did not see anything bad. I sent it to Melling who checked it out and said the pump was fine, but sent me a brand new one anyway. They said my pump had 34psi idle pressure and the bypass opened at 64psi. Same as the new one they sent me.

Today I installed the new pump and a new filter, thinking a clogged filter (engine assebly lube) might cause pressure issues as well, and ran it again with the 50wt oil. The idle pressure is better, around 30psi, but when I rev the engine it dips DOWN! So pressure is not building. What would cause this? There are no external leaks or open port plugs or anything to cause concern that I could see. What else should I be checking?

Here is a video of the idle and some small revs. Notice the pressure drop when RPM goes up. Ignore the water temp gauge. The coolant needs to be filled more and it was running for less than a minute.

RX-Ben

Sender is good?
Any chance to try another sender and or an alternate location?
A drop like that in a turn would mean the pickup is uncovered, but assuming you have oil, can't see that applying while idling. Is there an o-ring or anything special associated with the pickup that could be leak under pressure if not aligned correctly or something along those lines?

Kubs

It's a mechanical gauge connected right to the back of the block. When I set up the engine during assembly the pickup has 3/8" clearance to the bottom of the pan. The pickup is pressed in and held with a bolt. I put a small amount of rtv around the tube before pressing it in.

fatbillybob

Sounds like crack or bad seal pickup tube to oil pump inlet or bad clearances on the big rod ends and or crank walk.

Crepitus

I would say a restriction or on the suction side of the pump or excess clearance / spun bearing on the crank. Like BillyBob said ^ A leak pulling air in on the suction side could do that to.

btw; hate to see you have probs

geerookie

It's probably the o-ring between the pump and the pickup. It's pinched or missing.

Hi Volts Z06

It's ot the o-ring (which I hope it is) I would send the oil out for analysis to see if there is any evidence of bearing material. I had an almost exact issue with a new build two years ago and it turned out it was a spun bearing.

Can I ask who built the motor?

Kubs

This is not an LS, I have never seen an o-ring on a regular SBC pickup. The tube itself looks fine I checked it over before I put it back in. That only leaves a spun bearing I guess....

I had a machinist set everything up and I assembled the engine.

sperkins

Gen 1 smallblock?

Couple of things to check:
Oil pump pickup clearance to pan should be +/- 3/8" to prevent foaming/cavatation. I always used the Play-Doh method to check.

Oil passage plug under the rear main in the block - make sure it's installed.

Pull the valve covers while the engine is running to verify lack of oil pressure at the top end.

Improper oil level


If you have an oil pump priming tool, pull the distributor and test it manually.

Kubs

Yes a gen 1 small block.

Pickup was exactly 3/8" off the pan when I first built it, and I doubt there would be that much difference from one pump to another of the same part number so I did not check this time.

Oil passage plug was installed by the machinist who did all the work on the block.

I did not think to pull the valve covers, but that is a good way to check also.

Oil level is where is should be, but I have a fill level plug on the canton pan I can double check to make sure it is at that point.

I did test the pressure manually with a prime tool and drill, but the cordless drill I have was only able to muster 10psi on the gauge while priming.

Crepitus

After re reading, at first there was a low op at idle, thicker oil helped that. ok now the prob is op drops off as the engine revs. There are 2 oil pumps in your engine, the gear pump in the pan and the centrifugal pump, the crank shaft. the gear pump is a positive displacement pump. Pretty linear output, the crank is a centrifugal pump with a curved output profile. a lot of stuff shapes that curve, clearances and main groves ect. If the crank slings out at high rpm faster than the op can supply it galley psi will drop. A lot of builders find a little advantage using the minimum pump possible but it takes a lot of pump to supply a loose bottom end at higher rpm. thin oil makes it even harder. I would drain a couple oz of oil out of the bottom of the pan. Pour it in to a big glass pickle jar. shake it around and shine a light through it, look for metallic sparkle. do the same with the oil from a cut apart filter. Any detectable babbitt or copper (or what ever the hell they make bearings from these days) is bad. I hope some of this is helpfull.

Crepitus

The early sound from a spun rod bearing. Out of gear raise the rpm to 3-3500 rpm then lift out of the throttle. listen for a breif rattle from the crank case as the revs drop. If you cant hear anything = inconclusive if it rattles you are real close to putting a rod out the side

Kubs

No knocks or noises but I did find some bearing material in the oil.... Looks like the bottom end is coming apart again. Good thing I caught it in time though.

ScaryFast

Ugh. Sorry to hear, bud.

Kubs

Thanks for the insight last night.

Just to update, I am looking into the harmonic balancer being out of balance or broken as a cause for the main bearings going out.

LateBreak

What kind of oil filter are you running? Have seen numerous people lose pressure due to failed filters. It won't bring your bottom end back, but it might help explain the original cause if its not the balancer.