oil pressure problems

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AJ71DUSTER

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I have a 408 small block my oil pressure will start out at 25lbs of pressure at an idle and go to 55lbs at 2500 rpm's. then the pressure will slowly drop to 5lbs let the engine idle for 3 to 5mins and it returns back to 25lbs of pressure the engine only has 1100 miles on it

things replaced oil pump and filter

I also check the the sump and the oil filter housing for blockage but found nothing

I had to replace the main bears and torque convertor to a 3000 stall speed due to a balloning effect but i don't think that this is my problem

has anybody had this problem or any ideas to correct it

thanks
 
green1 said:
If the converter ballooned, it took out the thrust bearing.
Click to expand...

Yeah it usually does but he said he changed the main bearings.

AJ71 what were the bearing clearances? What weight oil are you running?

Have you tried another gauge to make sure your gauge is working correctly? Do the lifters ever rattle (I'm assuming their hyd.)
 
How about the plug in the oil galley in the distributor hole. Was your block boiled out when it was built or did the machine shop use a pressure washer to
blow out the oil passages to clean them? toolman
 
I dont follow you.. It idles at 25psi. It reads 55psi at 2500 or higher. Then if you let it idle for a while, it drops to 5psi? And if you rev it or drive it, it goes back up to 55psi and then when it goes back to idle it's at 25 again unless you let it idle for a while? That sound right?
 
My old chevy started doing that after an engine swap. What it was, or seemed to be, was I had just bought a cheap generic filter, when I went to the dealer and bought the actual filter for that engine, it went away. It just started doing it again recently, tells me its time for an oil change. lol.
 
Thanks for all the replies,i listened to the machine shop and they told me that no need for checking the bearing gap foolish me.the only resson that the crank was at the shop was to be polished no damaged at all due to balloning. i bought the short block from Jegs so i can only assume that the block was correctly cleaned.
the gauge, line and fitting that goes into the block have been all replaced and bled out. the only lifter noise that i had is at first start up after reinstalling.here is the list of filters that i have used, fram,K/N and purlator still the same problem and every time I have changed filter the oil was changed to10w 30 penzoil.at a hot idle i have 25lbs of pressure it's only drops when I'm running at 2500rpms and will return back to 25lbs when the engine returns back to idle about 3 mins later.
 
It sounds like your sump pickup could be cavitating. Have you checked if the sump is touching the bottom of the pan?
 
I still dont get it. It has 25psi at idle... then when you HOLD IT AT 2500 it DROPS to 5, thne comes back to 25 if you let it idle? I apologize, but I'm struggling to understand this as written...
 
Under load the crank is pushed away from the block and this would cause the preasure to drop at higher RPM'S. I had a worn out 390 ford that had good preasure at idle but cruising down the road it droped to 5 PSI. Let of the gas and it would jump up to 35. Replaced the worn out mains and all was good. I wonder if your main clearance is excessive?
 
Thanks again,I have replaced the line,gauge and fitting that goes into the block,trust me I went as easy as possible first but with no luck.just to tighten this up a little bit, this problem has just started after I replaced the torque convertor, new main and rod bearings for the first 1000 miles this problem did not exsist.so from what I read there what is the possiblty of the sump being to high would this also cause cavitating? also if the bearing gap was to big would this not cause a low oil pressure at a hot idle? is the oil that I using to thin 10w30? I have also read to help stop the cavitating would be to add an extra quart of oil any thoughts? just so you guys know i have oil pan and header gasket on auto order form my parts store(just a little humor) thanks
 

next time you change your oil you should be able to reach the pickup through the drain plug hole and probably adjust it closer to the pan with a long screwdriver. I have always used 20W-50 on all my small block mopars. That may not work in the winter where you live. Try the higher viscosity oil before you try to change bearings.
 
I'm sorry. My info was incorrect. The plug I was talking about is in the block below the rear main bearing. I can dig up some more info if you need. toolman
 
toolmanmike said:
I'm sorry. My info was incorrect. The plug I was talking about is in the block below the rear main bearing. I can dig up some more info if you need. toolman
Click to expand...
Correct. The oil gallery plug is INSIDE the rear of the block. You need to remove the distributor to see it. With the Dist removed peer down inside the hole with a flashlight. I took a picture for a visual. Without this plug oil pressure will suck and your valve train will roast.

DSCN1871.JPG
 
toolmanmike said:
I'm sorry. My info was incorrect. The plug I was talking about is in the block below the rear main bearing. I can dig up some more info if you need. toolman
Click to expand...

I put some thought into your post here about a plug under the #5 main cap that the OIL PUMP bolts to. I have 4 small blocks and NONE of them have this Cup Plug and my oil pressure has always been just fine.

I pulled out the book HOW TO BUILD BIG INCH MOPAR SMALL BLOCKS and on page 26 it shows this plug, but I am pretty sure that it is talking about the R3 Block or the Replacement 340 block from Mopar, which to my knowledge has several ways to route the oiling.

Someone please step in here if I am incorrect, I pulled 2 of my blocks #5 main caps just yesterday to see again for myself and NO there is not a cup plug.

The book says if the CUP PLUG is left out that Oil will bypass the filter and the oil pressure will be very low or none at all.???????? Again I am pretty sure it is talking about the R3 or Replacement 340 block from Mopar.
 
First, 10W-30 is just fine, second, how much actual oil is in the pan before you start the engine and experience the problem, third, if you've got 4 quarts in it now put 1 more in and see if the problem goes away. If it does that could signal other requirements like using a windage tray (designed for strokers) or making damn sure the oil pickup is damn near touching the bottom of the pan. If after adding the extra quart nothing changes then your "only" option is to start off by checking the main bearing for excessive clearance before you toast that new crank.

Terry
 
Mad, you need that plug. If you ran them wihtout it, there may not have been an indicated problem... but the oil was never filtered either.... I still have no definitive ideas about the OP's issue...lol.
 
Thanks for the replies,i had a busy week, i pull the distributor and the plug in place, i also added an extra quart to see if this would corrected my problem a presto the oil pressure stayed steady all the way to 3000rpm. good right!!!!! oh no not that easy.i started to brake then the oil pressure dropped right down 5lbs again so i when i went to accelerate quick the pressure drop out again, so i do believe that i have to much oil and it's hitting the crank and causing problems.Sooo i will check the sump from the above advice but if this does not work the next step is to pull the engine out and check the bearing clearance on the mains. could someone tell me what the clearance should be? thanks for all the info
 
Main bearing clearance is .0005 - .002 for a stock rebuild and up to .003 for race. I shoot for .0015 on my street builds.
 
Maybe a crack in the oil pump pickup where it screws into the block?
I FUBAR'd one trying to get the sump closer to the bottom of the pan. (marine application)
 
Check the oil pump before you remove it. Make sure it's sitting flush on the main cap. I aim for .00015-.0025 on mains and .002-.0025 on rods.
 
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