Low oil pressure, new engine

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Tomfury68
Posts: 4
Joined: Thu Jun 11, 2020 7:09 pm

Low oil pressure, new engine

Post by Tomfury68 » Thu Jun 11, 2020 7:42 pm

At my wits end, well almost. I have a 76 x 90.5 engine that i put together. Using an empi aluminum bubble top case, aa i beam rods, 26mm schadek oil pump, cb performance panchito 44 heads, new dog house oil cooler, cb performance cam and 1.25 ratio rockers. Broke cam in with straight 30 weight oil with zinc. I had an oil pressure guage hooked up and pressure was fluctuating between 75 and 0 psi during break in, thought that was strange and oil was just low, fires it off and finished cam break in, oil pressure was normal. Installed engine in car, drove about 20 Miles, revved it to about 5k rpm once to break rings in got home and oil light was on at idle. I figured it was the switch and out a guage in it, max cold psi was 50 at 3krpm 0 to 5 at idle, swapped pumps for a 33mm that i had laying around, new, only slightly better. Tore motor down and all the bearings looked great. Replaced them anyway because i had them on hand, figured i wasnt going to have to tear it down again. Just test ran it with 30mm pump and 20 50 oil, 50 psi max cold at 3500rpm then quickly dropped to max 20 psi at 4000k rpm 0 to 5 psi. I swapped the oil control valves and springs that i had. Was originally using empi set then factory set no changes. I measured the crank and its in spec, no weird noises. I have a full flow oil set up that is tapped into the case, swapped oil filters to a wix, no change, pump is plugged and case oil pump outlet plugged. Any thoughts, i dont know what else to check. Im thinking some oil passage blew in the case when i revved it to 5k. Was hoping i spun a rod bearing but no obvious solutions for me. I've built several engines v8s , sixes and several vw. Just stumped

Kafer_Mike
Posts: 420
Joined: Fri Oct 04, 2002 3:01 am

Re: Low oil pressure, new engine

Post by Kafer_Mike » Fri Jun 12, 2020 12:56 pm

Have you checked the pressed fit of the oil pickup tube into the case? Also, if you have deep sump, check the oil pickup tube extension's depth and seal to the main oil pickup tube. It could be sucking in air at either place as RPMs increase and the oil level in the case drops. Once RPMs drop and the case refills, pressure returns. :wink:

66brm
Posts: 382
Joined: Mon Apr 12, 2010 8:55 pm

Re: Low oil pressure, new engine

Post by 66brm » Sat Jun 13, 2020 8:24 am

I agree, I think you are sucking air, either the pick up or the pump itself

Tomfury68
Posts: 4
Joined: Thu Jun 11, 2020 7:09 pm

Re: Low oil pressure, new engine

Post by Tomfury68 » Sat Jun 13, 2020 9:17 am

Ok, thanks. Im hoping its a poor oil pump fit. I have a deep sump but didnt install it yet. I checked the oil pickup tube the 3rd time i tore it down seemed really tight. I tried to pressure check it but just made a mess. Strange thing about it is it was fine until i revved it up. I thought i might have spun a rod bearing, even hoped in fustration but everything looked great. I installed another pressure boosting kit yesterday with a really strong bypass spring. Got 40 psi cold at 3k rpm then dropped to 25psi max ay 165 degrees, 0 psi at idle. I figured with a 30mm pump and high pressure springs i would blow the filter up. Thinking of o ringing the oil pump inlet just to eliminate the possibility of sucking air. Is there any passage that can rupture from too high oil pressure? Thanks for any help

Tomfury68
Posts: 4
Joined: Thu Jun 11, 2020 7:09 pm

Re: Low oil pressure, new engine

Post by Tomfury68 » Sat Jun 13, 2020 10:15 am

Just ordered an o ringed pump, hopefully it will do the trick, I'll post the results. Have to tear the engine down again. Going to first bypass the filter. Im having to clearence the back of the pumps due to cam bolt interference, any suggestions on the proper way of doing that. I cant imagine oil leaking past gear shaft, thinking improbable things now

Bruce2
Posts: 6943
Joined: Sat Oct 13, 2001 3:01 am

Re: Low oil pressure, new engine

Post by Bruce2 » Tue Jun 16, 2020 2:13 am

Ignore your gauge reading at idle. It is not accurate. If the idiot light is off at idle, you are good.

Ol'fogasaurus
Posts: 15790
Joined: Tue Nov 14, 2006 1:17 am

Re: Low oil pressure, new engine

Post by Ol'fogasaurus » Tue Jun 16, 2020 9:32 am

Bruce2 wrote: ↑
Tue Jun 16, 2020 2:13 am
Ignore your gauge reading at idle. It is not accurate. If the idiot light is off at idle, you are good.
I agree with Bruce. The idiot light doesn't go on unless the pressure is less than 6 or 8 pounds with oil pressure supposedly going up 10# for every 1000 RPMs up to something like 60# or maybe to the 70#s. Electric gauges have a long tendency to have problems so I would recommend that you put in a temp mechanical one just to verify. They are not expensive and are more accurate than even the idiot light.

Just before I lost one of my engines the mechanical gauge started to show problems with oil pressure going down grades (plenty of oil in the sump). I headed back to camp and as I came down the last hill before getting to camp the gauge went to 0. About a quarter to have mile later, just as I entered camp, the idiot lite came on but the engine was already toast; it was a P-poor rebuild that I had bought from a friend who had it built. He had paid for a complete rebuild that was supposed to have brand new internals and other goodies... he had gotten stiffed!

I seem to remember that the bowl on the electric gauges need to be facing down not up but that was with the older gauges so I am not sure what is going on now days.

Lee

Up graded the max oil pressure as things may have changed some since I built my last one.

Tomfury68
Posts: 4
Joined: Thu Jun 11, 2020 7:09 pm

Re: Low oil pressure, new engine

Post by Tomfury68 » Sat Jun 27, 2020 3:31 pm

I was running a mechanical guage with engine out of car. The oil light is what alerted me there was an issue. Id be happy with 10psi at idle. Cold pressure max is 40 psi at 3500 rpm quicky dropping to 20 max 0 idle. If it was an old used motor i wouldnt care but everything is new. O ringed pump is supposed to be here monday. Any known areas of internal leakage i can check for? Rod side clearence is 016. I have tried 26mm to 33 mm pumps, swapped out oil control valves, springs and oil filters even bearings. Has anyone ever had a defective crank shaft or blown out oil passage. There is some hidden gremlin here. Any input considered and appreciated. I even switched guages

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