Why would oil pressure rise when I let off the gas?
05-02-2008, 09:19 PM
#1
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Why would oil pressure rise when I let off the gas? lets say i'm at 45psi at 2k rpms, Ill be in 4th gear and floor it to about 4k rpms and the oil prssure stays around 45-47 but will go up to 50-52 when I let off the gas. Anyone have any input on that?
Thanks
Dave
Thanks
Dave
05-03-2008, 03:06 AM
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Perfect example here. Im at 47 psi at 3000 rpms. I run it in 3rd and go to 4500 RPMS. the oil pressure slowly crept to 42 psi and as soon as I let off went back to 47 psi. Im baffled.
Thanks
Dave
Thanks
Dave
05-03-2008, 03:19 AM
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the only thing i can even remotely figure is that there is a delay between your gauge reading and the actual RPM of the engine.
oil pressure is...pretty RPM dependant. so it should rise when you lift.
oil pressure is...pretty RPM dependant. so it should rise when you lift.
05-03-2008, 04:11 AM
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need to know mods, anything done recently, last oil change, oil & filter type, any additives or junk in the oil, oil level, and when did this start and does it do it sitting still and moving. Basically, the oil pressure should rise with RPM.
05-03-2008, 04:16 AM
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new motor which has me worried. shimmed stock pump. I have an image of exactly waht it is doing. Coil oil pressure is 60 at idle and down at 20 while hot at 235deg. This isnt a guage issue im pretty sure because the SECOND I let off the oil pressure goes right up. This is for my vette
Last edited by TT_Vert; 05-03-2008 at 04:22 AM.
05-03-2008, 04:57 AM
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motor built by someone else but I plastigauged the mains at .0015" and rods around .002 to .003'. I personally shimmed the oil pump .090". I'm using 15w-50 now with a napa gold (wix) oil filter.
dave
dave
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05-03-2008, 11:13 AM
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I know on old small blocks when this happens sometimes a bearing is spinning or getting ready to spin. Not saying that is what it is but have seen this before.
05-03-2008, 06:20 PM
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20 to 25 psi at idle (800 rpm) is OK as long as it pumps up. Was it dropping when you let off the gas with the 5w 30? To me, none of this is good on a new engine, what does the builder say?
05-03-2008, 06:24 PM
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My idle is 715 RPMS. The builder was a local guy who I no longer have contact info for. Basically it was a new longblock that I tore down to inspect clearances on. The oil pressure seemed to do the same thing w/ 5w30 as it does 15w30. IN fact, it has 3 quarts of 5w30 and 2 of 15w50 right now. It seems when cold, the oil pressure will increase just fine w/ RPMS but when it warms up it does not.
Dave
Dave
05-03-2008, 07:03 PM
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did your problem just start?? im kind of baffled as to what it can be. Only thing I can think is the thrust bearing is allowing the crank to walk back a bit but would that cause this really??
Dave
Dave
05-03-2008, 08:20 PM
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Well, the inevitable happened. The car started to knock 
Was running so good too. Anyone have any idea what would cause a bearing to spin or a rod knock when all the clearances seemed to check out fine?? Id hate to have to put this thing together again to find out I fucked up.
Thanks
Dave
Was running so good too. Anyone have any idea what would cause a bearing to spin or a rod knock when all the clearances seemed to check out fine?? Id hate to have to put this thing together again to find out I fucked up.Thanks
Dave
05-05-2008, 03:28 PM
#17
Clearances too large, or a spun / burned bearing. When theres no power applied the crank is centered in the mains and the oil pressure is good. But once you apply power, theres side loading on the crank and theres a larger gap between the bearing and the crank and the oil just flows out and down into the pan.
05-05-2008, 04:01 PM
#18
Clearances too large, or a spun / burned bearing. When theres no power applied the crank is centered in the mains and the oil pressure is good. But once you apply power, theres side loading on the crank and theres a larger gap between the bearing and the crank and the oil just flows out and down into the pan.
Seen this before in other engines. Main bearing clearances too large. Bad news is that it will only get worse.
05-05-2008, 06:42 PM
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mine does it to, im thinking possibly pinched O ring on the pump allowing air in, or the gasket on my oil pan is letting air in and leaking pressure that way. Changing all that this weekend, ill let you know if it fixes anything. Oh yea im changin the rod bearings also while im under there swapping rod bolts.