robster

not sure on this one. just rebuilt my engine. installed 243 heads, 534 cam, headers. on cold starts my oil pressure is typically around 50 psi. warm at idle is more like 20, and here recently when driving, it stays around 25. using fram filter and 5w-30 synthetic

RARON455

iTrader: (35)

Watch your pressure carefully, the old rule of thumb is 10LBS for every 1k RPM.
I will say that seems low, Mine is around 70 when cold 40lbs when warm, but I run a MELLING 10296 HIGH volume, But even with my stocker when I had it my pressures were higher.
Did you rebuild it,, Are you certain that the pickup tube O ring was not pinched or nicked?

DGageSS

iTrader: (9)

depending on what you mean by rebuilt, you should not put a synthetic oil into a new motor. best to use old school oil. however, if you didnt touch the bottom end, then i dont see how the pressure would change like that just from a swap, did you put a ported oil pump on there?? like ^^ said did you check the o ring, if its not a new motor, then what was your pressure prior to the rebuild? need more info, glad to help.

robster

yes i rebuilt it. i made sure the oring didnt get pinched or cracked. i heard about that before i started the build. all cam bearings were installed correctly with oil ported lining up perfectly and rod bearings are perfect and caps back on the correct rods. it tends to fluctuate alot. after the 1st 1000 miles, i changed the oil and my pressure stayed around 40 and within the past 1000 miles it has moved. there were no abnormal metal shavings or anything in the oil. engine doesnt make any rattle or tapping noise when cranking or on cold starts.

DGageSS

iTrader: (9)

ok did you check your bearing clearances, the looser the less pressure. i would still say you shouldnt have put synthetic in unless its like a race oil but most here use, VR1 or Joe Gibbs or something equivalent i dont no if you did... low pressure on a new motor from what i no is from too loose of bearings and thats what it is usually. remember this is aluminum it expands when heated which is why u have a loss at warm idle.

robster

all clearences were good. engine had 158000 on it. i could still see the factory cross hairs in the cylinder walls. everything was torqued properly and double checked everything. i work on BMW's for a living. LOL. just havent ran into this very often. Never on a new engine.

DGageSS

iTrader: (9)

all i can think then is the synthetic oil then...but idk maybe someone else can help.

RARON455

iTrader: (35)

I would get that synthetic out of there, and run a good break in oil, you can get comp cams break in oil from summit or jegs, Or you could get the break in additives and put it in with your conventional oil of choice..
I didnt catch the synthetic oil part of your post,, But being a new engine, You want to break in and seat all the parts properly. The break in oils have alot of the zincs and phos. additives that help promote ring sealing ETC... BY all the clearances are good,,, do you mean within spec.? If they are on the big end it will not have good pressure. DID you check it with plastigage or indicators and mics? DO you have any of the clearances?

robster

i didnt use synthetic for the break in period. i used regular castrol. i didnt write down the measurments. only thing i can figure is maybe i overlooked damage to the o-ring. i checked everything out beforehand. also, i wonder if there might be a different o-ring size than the one that came with the new oil pump since its not a factory part. like maybe the aftermarket one is a little off and not sealing completely

RARON455

iTrader: (35)

I do know for a fact that there are two different orings for LS pumps, my melling came with two and they are definately different sized, that may be the issue.

robster

yea. guess ill be pulling the pan and checking it out. atleast that easy

DGageSS

iTrader: (9)

ya but in my opinion its no way an oring, if you have 50 psi cold pressure then your oring is fine, if it was pinched you would have like 8

DiabloFormula

iTrader: (58)

Its the o-ring, I know it sucks but trust me I just went though this exact thing, replace it with the new blue GM updated o-ring, if you already did then it is pinched, even the littlest bit will do this and let air get by.