Register now to get rid of these ads!

Drop in oil pressure on new engine

Discussion in 'The Hokey Ass Message Board' started by Paul Y, Feb 12, 2011.

  1. Paul Y
    Joined: Dec 29, 2006
    Posts: 633

    Paul Y


    Looking for a quick bit of advice from those more learned than I.

    Fresh rebuit small block, started up to run cam in and oil pressure is steady at 50lb. Idle set at 2500.

    Timing roughed in but pretty close.

    After about 10mins of fast tick over oil pressure started to drop down to 25lb and stayed there.

    Temp is around 200.

    Am I being paranoid over a fresh build or is this an indication of a problem??

    Any advice??

    Many thanks

  2. HommerSimpson
    Joined: Jan 16, 2011
    Posts: 29


    Does not sound good...Rule of thumb 10 psi for every 1000 rpm.... Factory most engines have 45 - 60 idel 25 is fine.. but if its not going above 25... then you need to start checking things.. are we working on a SBC ?
  3. Mr48chev
    Joined: Dec 28, 2007
    Posts: 30,866


    Does it come back up when the rpm's go back up? 25 isn't bad at an idle most of the time with a sbc.

    OK, I reread the question again, If the rpm's were still up the pressure should have stayed pretty close to the same.
  4. Good advice so far. Yea a major pressure drop without an RPM drop isn't a good thing.

    Are you using a mechanical pressure gauger? Check that the line hasn't come loose, another thing that you could do is disconnect the line and spin the motor over to make sure there isn't something blocking the line.

    Electric gauger? Once I had one that i thought i screwed up and when i checked the sender was loose, tightened the send and everything became copacetic.

    Next start to dig into it.

    maybe check the bypass on the pump and the pickup screen. Sometimes a piece of grit gets in the bypass and the piston sticks or something blocks the screen.

    After that you start to look for spun bearings. If everything wasn;t sized right even new bearings can spin in the journals.

    But hopefully you wont get that far.

  5. Dan Timberlake
    Joined: Apr 28, 2010
    Posts: 1,372

    Dan Timberlake

    Like others said, 25 psi at idle with hot oil may be normal for the application.

    If it is indeed low, it suggests the possibility of greater than desired clearances somewhere in the engine.
    Engines with rods-n-mains worn deep into the copper can have decent oil pressure until the oil gets warm, and thin.

    Were the cam bearings new?
  6. Paul Y
    Joined: Dec 29, 2006
    Posts: 633

    Paul Y

    Idle still at 2500 as want to run the cam in for about 20 mins before letting it idle at 800, so rule of thumb 25lb @2500 is ok?

    New cam bearing, new crank and bearings etc. Sounds absolutely fine running with no rattles etc.

    Has a mechanical and electric gauge, the mechanical one is the oem dash gauge, both read around the same.

    Will see what it the pressure is at 800 tomorrow, just wondering if there is a anything that could be blocking the pick up or if the assembly lub is causing the problem.

    Yes it is a sbc, think I am just used to my big block having a lot more pressure and new engine jitters!

    Let's see what it settles down too tomorrow once I have finished running in the cam and set the timing and idle correctly.

    Thanks for the speedy replys.

    Last edited: Feb 12, 2011
  7. RNess
    Joined: Sep 12, 2010
    Posts: 167


    I had an oil filter do that once, pressure dropped, changed to new oil filter, solved problem. Just saying.
  8. it should live until your cam is run in. Then find your problem and tell us so we can ad it to our books.
  9. randydupree
    Joined: May 19, 2005
    Posts: 666

    from archer fl

    saw the oil filter in half and pull the paper out and inspect the paper for metal,if its full of metal pull the engine and start over
  10. HommerSimpson
    Joined: Jan 16, 2011
    Posts: 29


    When you shut it down again.. pull one of the valve covers...look in the lower corners of head.. you should see some fresh puddles of oil... clean your finger.. and put a dab on a peace of paper.. and look for shinny things... aluminum.. brass copper.....on new engine at 2500 rpms.. myself.. if it read 25 psi id be very worried... it should be up around 55 - 60.... But that rule of thumb.. 10 psi/ 1000 rpm is what an engine needs to live... its only a rule of thumb... as if you wanted an engine turning 8000 rpms.. you better have close to 80 keep everying lubed...25 psi on new engine at 2500 rpm is not good... Hope it is something simple...
    Last edited: Feb 12, 2011
  11. Shamedevil
    Joined: Dec 16, 2008
    Posts: 270


    I had the same problem 6 months ago praying it was something minor but it wasn't..........bad clearances,rods & mains got wiped out along with the cam & lifters. Only 500 miles on the 327. Make sure you use break in oil, Brad Penn or Joe Gibbs's worth it..........I had a $3500 mistake.
  12. sdluck
    Joined: Sep 19, 2006
    Posts: 2,883


    Put a good oil filter on it try wix,not napa gold real wix.The filter may be clogged with assembly lube. What pump and oil did you use.What are the clearences.Whats the history on the motor?
  13. 61falcon
    Joined: Jan 1, 2009
    Posts: 772


    let that thing run at cam manufactures break in rpm, let it cool and change oil and filter and run it to temp and see where oil pressure is at hot idle. what type of oil pump are you running, high pressure, high volume, stock?
  14. x2 on that.. asembly lube and little bits of metal from breaking in the engine can clog up things quick... change the oil and filter and see what happens...
    what kind of oil filter you runnin? please say its not a fram....
  15. Long shot here ... had a friend install the oil pressure sender fitting using teflon tape. Turns out a bit of tape was "flapping" around and occasionally blocking the sender fitting.

    I actually wouldn't run it any more until you check the oil/oil filter for metal filings/particles. If I understand you right, the oil pressure dropped but the RPM's didn't ... that's not a good sign. In order to minimize the damage ... find the cause now before you put more time on the engine and possibly cause more damage (if indeed any damage has been done up to this point).

    Did you use break-in lube? Did you preoil the engine before firing? Had the engine been sitting for years after the rebuild and is just getting fired now?

    Hope it is something simple and that no damage has been done, but I would NOT fire it again until you can verify the cause.
  16. studebaker46
    Joined: Nov 14, 2007
    Posts: 689


    another problem i have had with a smallblock is the pickup is loose and turns sideways. just a thought good luck and let us know what happens..... tom
  17. I'll throw some chips on the table here. Pretty simple. Let the engine cool down overnight. Restart the engine and observe the oil pressure readings. At this point the pressure should duplicate the original readings upon the first fire up. If the readings don't match you have a problem. Now I'm going to make a suggestion on what I see to be a common problem on the small block Chevies. The 3 oil gallie plugs at the front of the block behind the timing chain are press in plugs. I have seen the time when 1 of these plugs will fall out after the engine is started and run in. It will drop the oil pressure in half. Now I know this is a 1/2 inch plug but the oil passage at the back of the block is about 3/16th and that will result in about 50% loss of pressure. I hope this helps out >>>>.
    Last edited: Feb 12, 2011
  18. Retro Jim
    Joined: May 27, 2007
    Posts: 3,859

    Retro Jim

    What you might want to do is change the oil and check it over real good with a magnet to see if you have some metal shavings in the oil unless you have a magnet drain plug . Also change the oil filter for a new one . Cut the oil filter open down at the lip so you can remove the case and take a look at the filter and see if there is a problem there .
    If the bearing aren't the right thickness that will cause a change and you can get lower oil pressure .

    When the engine was rebuilt , did you have the block cooked and cleaned at a machine shop or did you do it yourself ?

    I rebuild engines and to loose that much oil pressure on a newly rebuilt engine means something is wrong ! New rebuilt engine will hold 50 to 60 psi for a while but as you put more mileage on the engine , the oil pressure will drop to a normal reading of around 40 to 45 lbs at idle and higher as you increase the rpms .

    I also see you say the pick up tube moves . With a sbc engine you are suppose to measure the oil pick up to be about an oil pan gasket from the bottom of the pan , then you are suppose to "tack weld" the pick up tube to your oil pump . This just might your problem . That pick up tube might have worked it's self loose and not drawing the oil up like it should be !
    just a thought !

    Retro Jim
  19. I built myself a simple "run-in stand" for my engines (all I play with are SBC's). I had a ton of issues with an engine once and was I ever happy I had built that stand ... I had the pan and intake off numerous times before the engine was installed in the car. Makes it so much easier when break-in issues appear.

    That aside ... there are a lot of possible causes being brought up here ... I would suggest dropping the pan and checking the pick-up tube (you can also plastigauge and visually inspect the mains and rod bearings at this point too). Someone mentioned the oil galley plugs behind the timing chain (if you drop the pan, now is the time to also remove the timing cover). As I mentioned before, if this was me, I would be searching for the cause before firing it up again.
  20. Norwegian 49 Mercury
    Joined: Oct 25, 2008
    Posts: 71

    Norwegian 49 Mercury
    from Norway

    We almost reassembled a big newly overhauled NewHolland Tractor engine last week. But we tested the oilpressure with our old testinstrument. The oilpressure was just fine. But the new fancy instrument ended its life flying across our parkinglot...
  21. Gman0046
    Joined: Jul 24, 2005
    Posts: 6,259


    Another reason to buy a crate motor. How many threads like this have we read???
    Joined: Jan 13, 2004
    Posts: 2,769


    Where are you taking the pressure reading from,back of the intake at top of oil galley ,above oil filter, front above timing cover ? A lot of home rebuilt engines I have disassembled have been missing the drive -in plug in the oil galley at the rear of the engine. You can spin the oil pump with a preluber and diagnose the problem ,they by not running it and causing more damage. Oil pump bypass,oil filter bypass,various plugs,wrong design lifters,large rod side clearance,screwed up gauge,screwed up filter,those and more could be wrong . IMPORTANT do not run it anymore until you find the problem, use a pre-oiler till you find the problem. Best of luck
  23. Paul Y
    Joined: Dec 29, 2006
    Posts: 633

    Paul Y


    Many thanks for all the reply's this is the current state of play.

    The oil pressure take off is from the rear of the engine for both gauges. Took the adapter out and checked that it was clear as I had used PTFE tape on the thread. All clear.

    Took the rocker covers off and felt the oil in the return. Clean with no metal fragments in it.

    Took a chance and fired the engine up again to finish running in the cam. Oil pressure was around 60-70lb at start but after the final 10 minutes of break in this had dropped down to 25lb. It did not suddenly drop as it did the previous day which is making me think that it was me 'thinking' there was a sudden drop due to being busy checking for leaks etc.

    Had to be Dads Taxi for the rest of the day so not had a chance to drain the oil and change the filter.

    Filter is not Framm, cant remember the make but the box is very proud of the fact that it is 'Made in the USA'.

    Will probably not be doing anything else till next weekend but will update once I have discovered what the problem is.

  24. JohnEvans
    Joined: Apr 13, 2008
    Posts: 4,883

    from Phoenix AZ

    Don't see what weight oil you are using. If something like 10-30 or lower that may explain things. Or relieve valve in OP not seating.
  25. coupemerc
    Joined: Jul 16, 2007
    Posts: 406


    Make sure that the oil pump attachment bolt/stud has not loosened and dropped the pump slightly.
  26. Richiehd
    Joined: Feb 4, 2011
    Posts: 14


    My experience tells me 25 psi, hot at idle is fine, as long as the pressure goes up with RPM. I have always said 10 lbs per 1000 rpm. Another point not mentioned in earlier threads is the oil you are using. If you are using Synthetic 5W20 that stuff is like water when hot, it will make a difference in your pressure. Probaly should be running 10-30 or 20W 50. depending on your location. Also I dont recall if you said this was a new oil pump or not. Is relief valve operating properly? It would not be the first one I have seen hung up.
  27. Paul Y
    Joined: Dec 29, 2006
    Posts: 633

    Paul Y

    Ok Here is the update.

    Changed the oil and filter and ran it up again just to check and got the same result....Oh Bother.

    Dropped the sump and took the oil pump off to make sure that the pressure releif valve was not stuck.

    All good but then noticed that there seemed to be a lot of heavy scoring on the rotor vanes...Oh dear this is not looking good.....

    With heart in mouth dropped the centre main cap....

    You all know what is coming.....

    Bearings shot, crank scored and me very very pissed off....

    As I bought the engine rebuilt I have some recourse with the builder but...

    Once again life has decided it is necessary to give me a swift kick to the Man Veg, good job they are still numb from the previous good shoeing that I have received.

    I must have been very bad in a previous life.....

    Last edited: Feb 26, 2011

Share This Page

Register now to get rid of these ads!


Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.