rebuilt sbc Oil pressure

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Sam71395

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Hello all, I'm kind of a newbie to rebuilding motors, I have a chevy 400 that has low oil pressure at idle when warm, when its cold it has 50-55 psi, when it gets up to temp, it drops to about 11-13 psi at idle (800rpm), when cruising (2000 rpm) it is at around 25-30psi, I know the general rule is 10 psi per 1000 rpm but this just seems really low to me. I plasti gauged the bearings and they were all within spec (i dont remember specifically what the measurements where but they where within specs from the service manual). the only bearings i did not replace where the cam bearings,(looking back I probably should have) but the engine was a lower mileage engine (98,000 miles) so I figured they would be fine. maybe these numbers are normal with a standard oil pump? should I have any reason to be concerned?
 

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That is on the lower side but should be ok. Assume you double checked it with a known mechanical gauge? About the only reasonably easy thing to do is install a HV pump.

Had the same issue on a 350 but at idle was less than 10 hot, 30 at speed. Used the same 15-40 oil. Rebuilder said run it he would give us another one if problems developed, none did. Was a business truck used hard for at least 100k.
 

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yes I checked with two mechanical gauges and got the same readings, I may switch to 20w50 for the summertime, it runs good except there is a small lifter tick at hot idle, im hoping the thicker oil will help with that. Is there anything else i could check that may affect the oil pressure besides the oil pump or bearings, I just want to make sure i am not missing anything.
 

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Rebuilt is a term that is easy to throw out there. What all was done with it? Any block work?
 

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maybe the more appropriate term would be "refresh", new rings, bearings, gaskets, new heads, new oil pump, new cam/lifters, no block work was done, this was a decent running engine prior to disassembly, just was tired, and leaked oil
 

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Since it's a refresh with no block work, perhaps run a cleaner through the oil system for 20 minutes to half an hour, no revving, just idling and then change oil and filter.

In my 81, not refreshed original engine, I run Valvoline conventional 10w30, cold about 40-50 psi, hot about 20 psi.
 

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I wouldn't be at all concerned about the readings you are getting,and wouldn't give the cam bearings a second thought. Cam turns at 1/2 crank speed, if your rod bearings weren't showing lots of wear I'm sure your cam bearings are just fine.
 

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I had a 283 with two stuck rings,no compression there,burned oil at 40miles per quart,and over 100k on motor Had 10 psi at idle,maybe 15,at speed 25psi.Drove it two years and junked the motor.Was still running.
 

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Try a different brand filter…
 

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Morning coffee spitballing here. Maybe pull the pan and check the oil pump and make sure the the pickup is nice and tight on the pump housing and/or not clogged with break in lube. Would give you a chance to look in the bottom of the pan and look for debris anyway.

How soon after break- in was the oil and filter change done?

If it wasn’t hot tanked, suppose the oil galleys and passages could be gunked up a bit- some cycles of fresh oil and filters in quick succession could help with that.
 

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it's about 20-25 miles since rebuild/break in, the filter is a wix, would the filter bypass affect oil pressure?
 

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it's about 20-25 miles since rebuild/break in, the filter is a wix, would the filter bypass affect oil pressure?
Wix is a good filter. Can’t speak to to the filter bypass specifically, but if it hasn’t been changed and replaced since break in, I certainly would. Do you know what pressure it was running before rebuild?
 

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Hello all, I'm kind of a newbie to rebuilding motors, I have a chevy 400 that has low oil pressure at idle when warm, when its cold it has 50-55 psi, when it gets up to temp, it drops to about 11-13 psi at idle (800rpm), when cruising (2000 rpm) it is at around 25-30psi, I know the general rule is 10 psi per 1000 rpm but this just seems really low to me. I plasti gauged the bearings and they were all within spec (i dont remember specifically what the measurements where but they where within specs from the service manual). the only bearings i did not replace where the cam bearings,(looking back I probably should have) but the engine was a lower mileage engine (98,000 miles) so I figured they would be fine. maybe these numbers are normal with a standard oil pump? should I have any reason to be concerned?
It'll run but this is one reason I may never have had issue with this.I never used stock oil pumps.
 

Sam71395

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Wix is a good filter. Can’t speak to to the filter bypass specifically, but if it hasn’t been changed and replaced since break in, I certainly would. Do you know what pressure it was running before rebuild?
it had a warning light but it never triggered the light, i have my temporary gauge hooked up to it. and i am talking about the bypass that bolts up to the block with the oil filter adapter, im wondering if that can cause an issue.
 

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