Results 1 to 26 of 26

Thread: excessive oil pressure

  1. #1
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default excessive oil pressure

    Guys I need help here figuring this out. I have been fighting an oil leak in the rear main seal area which I have posted here. I have done everything including a speed-sleeve on the crank where the rear seal rides.
    I have always thought my oil pressure was too high on this engine, but discounted it because of the stock gauge.
    Today I installed a new oil pump(standard pressure and volume) and installed a mechanical gauge inside the car. No change.
    The oil pressure reaches 70psi before I get to 3000rpm. At cruise it will stay right at 70psi-cold or warm it doesn't matter. If I understand the pressure relief valve and how it works, 70 is the magic number as far as max pressure before the valve bypasses.
    When I look at the FSM, it shows what looks like two relief valves, one in the pump and one by the filter-is that correct?

    I am at the point that I think I have a partial blockage somewhere in the system that is driving the pressure up-but where? And how will I find it?

    I have tried to blow pressurized air thru the oil galleries between the filter and pump and they seem clear.
    I really want to figure this out before the car leaves the garage again.

    Shoot me some ideas guys-please!!!!!!!!!!!!!!!!!!!!!!!!!!!
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  2. #2
    Rust Free'ish zKars's Avatar
    Member ID
    CZCC-12190
    Join Date
    Jul 2006
    Location
    Calgary, AB Canada
    Posts
    1,256

    Default

    Suspect the pres. regulator in the oil pump. Take it apart and clean/inspect.
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

    www.zKars.com
    www.calgaryzclub.ca
    Reference materials
    www.xenonS30.com

  3. #3
    Registered User beermanpete's Avatar
    Member ID
    CZCC-21519
    Join Date
    Apr 2010
    Location
    Northridge, California, U.S.A.
    Age
    56
    Posts
    631

    Default

    Your description indicates proper operation. The oil pressure rises with engine speed to the regulation point and then stays there as the engine speed continues to increase.

    What is the oil pressure at idle? It should be about 15 psi or so when the oil is warm.

    The relief valve in the filter is a filter bypass not a pressure regulator. It allows the oil to go around the filter if the pressure drop across the filter is too high. Normally this will only occur if you race the engine at start up (cold, thick oil) or if the filter gets restricted by too much dirt (change oil and filter more often).

  4. #4
    Low Budget/High Value
    Member ID
    CZCC-20342
    Join Date
    Oct 2009
    Location
    Washington County, OR
    Posts
    3,629

    Default

    Seems to me that that seal area is not supposed to get pressurized. Your oil pressure is good, the oil just doesn't have the proper return path to the crankcase. Looking at various pictures of the bearing cap and bearing, for whatever reason the gap between the bearing and the seal must be filling with oil faster than it can drain out. I would focus on that aspect of the situation, rather than oil pressure.

    But I've not had an engine apart so I'm just going off what would make sense if I designed an engine. Maybe Nissan did something different.

  5. #5
    Rust Free'ish zKars's Avatar
    Member ID
    CZCC-12190
    Join Date
    Jul 2006
    Location
    Calgary, AB Canada
    Posts
    1,256

    Default

    Clearly its not the pump if the switch made no change. Sorry for jumping to conclusions.

    Very suspicious that it stays at perfect 70.
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

    www.zKars.com
    www.calgaryzclub.ca
    Reference materials
    www.xenonS30.com

  6. #6
    Low Budget/High Value
    Member ID
    CZCC-20342
    Join Date
    Oct 2009
    Location
    Washington County, OR
    Posts
    3,629

    Default

    More on the oil behind the seal - I am fairly sure (not certain though) that there is a drain hole or slot at the bottom of the main bearing cap between the seal and the bearing. There's a gap between the seal and the bearing for sure, so no reason for oil pressure buildup. I also have faint memories of shining a flashlight in there while changing a seal and realizing that I could see in to the crankcase.

    I don't see any reason for oil pressure to have anything to do with the leaking seal. The oil should be fed in to the bearing, run out the sides and down in to the crankcase.

    Of course, I could be way off.

    Edit - there might be a way for pressure to build up if the drain hole (if it exists) was clogged. Maybe that's the issue.
    Last edited by Zed Head; 08-02-2012 at 12:00 PM.

  7. #7
    No more body roll! SteveJ's Avatar
    Member ID
    CZCC-5413
    Join Date
    Dec 2003
    Location
    Gainesville, GA
    Age
    53
    Posts
    3,651

    Default

    What if the PCV is stuck shut? Couldn't that raise the pressure from the buildup of combustion gasses?
    73 240Z
    74 260Z

    Blue's collection of tech tips - A great place to look for answers
    XenonS30 -The cheap source for FSMs
    Georgia Z Club
    Fiddling with Z Cars - Z car tips & tricks and pictures of my car-loving life.
    Steve's CARtography - Just car pictures.

  8. #8
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    Thanks for the ideas guys.
    The PCV has been checked.
    I might just have to live wuth a leaky engine. I cannot see myself tearing into the engine for the rear main seal again. I've replaced everything including side seals and oil pan gasket.
    The constant 70psi seems weird!
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  9. #9
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    Old thread-current problem. I have my engine out to look into my head problems and thought I would check my oil pressure on a stand without the engine running. I drove the oil pump with a large drill and monitored oil pressure with a new gauge. With the drill running full speed-2500rpm, oil pressure runs pretty constant 75 psi. I figure that 2500 rpm on a drill duplicates about 5000rpm engine speed since the oil shaft normally runs half engine speed. Even with the drill set at 1250rpm(should be 2500rpm engine speed), oil pressure is 75psi. I don't think that's right.
    II am going to check all oil passages the best I can without dismantling the short block, but that might be next.
    Rear main seal leaks at the seal ID. I tried turning the crank by hand while applying oil pressure and I can see the oil wanting to seep at the crank. Looking at the seal carefully I can see that it is in slightly cocked on the 6-12 oclock position, so I know that's an issue.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  10. #10
    Boat Anchor Repairman Captain Obvious's Avatar
    Member ID
    CZCC-24608
    Join Date
    Jul 2011
    Location
    Philadelphia, PA
    Posts
    1,845

    Default

    I don't know what oil pressure would be expected at what RPM and temperature, but I guess I wouldn't be surprised to get 75 psi at 2500 RPM on a stone cold engine in un-worn good condition with thick oil. You're clearly bumping against the pressure relief valve built into the pump, but that's not necessarily a problem.

    As for the leaking rear main seal, I don't think there should be any link between the oil pressure and the leak at the rear main. There's no way that seal should ever be seeing pressurized oil. The back side of that seal has gotta be open to the pan somehow. Been so long since I've been in there personally that I don't remember how, but it's just gotta be.

    The cocked rear main could certainly be an issue... Not sure how much misalignment your typical garter spring seal can tolerate.

    You said that you turned the crank while applying oil pressure and you could see it trying to seep. Does it do the same seeping when you turn the crank and there is NOT oil pressure?

  11. #11
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    Your right Captain, a cold motor or oil would drive up pressures, but my engine runs that high all the time--- hot or cold. I did this without the engine running and a NEW gauge to make sure this wasn't a false reading.
    The front of my engine was coated with a fine mist of oil dust from the front seal.
    The rear seal does need to be redone.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  12. #12
    HLS30A 17574 djwarner's Avatar
    Member ID
    CZCC-27817
    Join Date
    Aug 2012
    Location
    Central FLorida
    Posts
    405

    Default

    Steve, normal, warm oil with a standard oil pump you should see 14.2 to 17.1 psig at idle. At 2800 rpm you should be generating enough pressure to open the pressure relief valve in the pump. At that time the pressure should be 54.0 to 59.7 psig.

    Nismo does sell a high pressure regulator spring for this pump. I don't know what the specs are for that pump, but the stock spring should have a free length of 2.24". Fully compressed it should measure 1.54"

    The pressure relief valve (regulator) simply returns excess oil back to the inlet side of the pump. Our oil pumps are a constant displacement type. That is it outputs the same number of CCs with each revolution and generating whatever pressure needed to make that happen. Once the pressure is sufficient, the piston in the relief valve moves back, opening a port back to the inlet side of the pump. Once cracked open, the relief valve will trade off additional oil pressure for additional volume of oil bypassed until the volume of oil put out to the engine and through the relief valve equals the CC capacity of the pump. - or until the piston in the relief valve bottoms out.

    The piston bottoming out is exactly what happens with a cold engine starts with thick oil.

    At this point it would probably be worthwhile measuring the relief spring free and compressed to verify it is to spec. Also - the exploded parts drawing shows there are three washers in the nut-cap that are used to adjust the set pressure for the regulator. Removing one two or three washers will reduce the regulated pressure.
    1971 240Z HLS30A 17574 L24-021025

  13. #13
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    DJ,
    Thanks for all the good info. I've been down this exercise before and have traded out springs, pumps. Right now I am running stock pump and springs- but will verify. I've basically ignored the issue because it wasn't a low psi problem. Now I have my head off I want to make sure my high PSI isn't from a blockage.
    Not too many folks have had this issue , so not much to compare too.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  14. #14
    HLS30A 17574 djwarner's Avatar
    Member ID
    CZCC-27817
    Join Date
    Aug 2012
    Location
    Central FLorida
    Posts
    405

    Default

    Re-reading what I posted, I'd try to remove the washers in the nut cap first. They are actually called shims in the parts manual which usually indicates they are meant to adjust something. Since they are part of the bill of materials, all three should be in there even if they are not needed. Too many shims will raise the pressure.
    1971 240Z HLS30A 17574 L24-021025

  15. #15
    Boat Anchor Repairman Captain Obvious's Avatar
    Member ID
    CZCC-24608
    Join Date
    Jul 2011
    Location
    Philadelphia, PA
    Posts
    1,845

    Default

    How about pulling the valve cover off and seeing what kind of oil flow you've got up at the cam while you're spinning the pump? Might give you some insight into whether the pressure is high throughout the system as opposed to something restricting the flow closer to the pump?

    I'm thinking that if you get great flow out of the cam, then you've got an overactive oil pump. But if you've got 75psi at the pump and just a dribble at the cam, then you might have a problem somewhere in between?

    Just tossing out ideas...

  16. #16
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    Lots of pressure up top and a pretty shiny cam to prove it.
    Like I said, I have been battling this for a long time. I've been told that the pressure is NOT too high, but no one else runs a constant 70psi on a street motor. I have also been told that the high oil pressure wouldn't cause the crank seal leaks, but I have leaks both ends.
    I didn't trust my Datsun gauge and mounted a mechanical one to be sure. I did this latest experiment to verify gauge accuracy and to eliminate any pressure contributions from a running motor.
    I might just be done with this L24 block if I don't find something definitive. I have a L28 short block sitting on a stand that just needs some cleaning I believe.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  17. #17
    Low Budget/High Value
    Member ID
    CZCC-20342
    Join Date
    Oct 2009
    Location
    Washington County, OR
    Posts
    3,629

    Default

    I think that this was mentioned on Hybridz but oil pressure is really a measurement of resistance to flow. The whole lubrication is designed such that the ~40-60 psi average reading is an indication of proper flow. It's a secondary indicator and can be misleading. It doesn't guarantee flow, it assumes it. Ideally, we'd have flowmeters in the dash showing that oil was actually going where it should.

    If you have a stock pump, correctly adjusted, and you get high pressure all the time, then that might mean there's a restriction of flow somewhere. For example, if you installed your crank bearings backwards (I think it's possible for a few) the oil flow passage would be blocked, and pressure would increase. Or if your port to the head was blocked, the same thing.

    And the rear seal is open to the crankcase. So really shouldn't be affected by oil pressure.
    1976 280Z, with some minor modifications

  18. #18
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    You did help out a bunch Zed. I believe I have a blockage deep in the block somewhere. I know I have been careless before because I found a piece of foil in the bottom of my oil pan before. It was one of the sealing foils-possibly from an additive bottle. It was all balled up and beat up like it had been beaten around my engine. So maybe something else is partial obstructing a passage way?
    Unfortunately, there will be only one way to find it. I will try removing the end plugs and cleaning out the main galley first. I will run pressurized air thru there and hope something lets loose. The problem is that I won't be sure I did anything unless I find something. It might be a total tear down. Maybe I will find a bearing misplaced, but I don't remember having this issue from day one.
    One thing about fresher motors-they come apart without much fuss.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  19. #19
    Boat Anchor Repairman Captain Obvious's Avatar
    Member ID
    CZCC-24608
    Join Date
    Jul 2011
    Location
    Philadelphia, PA
    Posts
    1,845

    Default

    Well it really sucks to tear down the motor not knowing what it is your looking for, or even if there's anything at all. Could you feel comfortable with one assumption... The assumption that if there IS some obstruction somewhere, it is upstream of the pump. Between the pump and the filter?

    If you operate under that assumption, then maybe you could just drop the pump and remove the filter and blackflow from the filter holes back towards the pump and see if anything pops out? Make some sort of block off plate that you could bolt onto the filter location to facilitate an air or solvent supply?

  20. #20
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    I am going to make every effort to NOT tear it down and try what you are describing. Also remove rear galley plug to facilitate cleaning.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  21. #21
    Boat Anchor Repairman Captain Obvious's Avatar
    Member ID
    CZCC-24608
    Join Date
    Jul 2011
    Location
    Philadelphia, PA
    Posts
    1,845

    Default

    I've never studied the intricacies of the oiling system routing in the block, but that rear galley plug is post filter, isn't it?

    Also, someone mentioned the possibility of having the crank bearings in backwards thereby blocking off the oil holes. I'm assuming that crank bearing(s) with no lube would have spun long ago, right? There's no chance that this is the issue is it? Hey... I have to ask.

  22. #22
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    This is all learning for me Captain. I imagine the back plug is a clean out point.
    The 'How To Modify' books shows the oil schematic.
    As far as the bearings- in my case it might just be a partial covering of a oil hole that would do it.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  23. #23
    Low Budget/High Value
    Member ID
    CZCC-20342
    Join Date
    Oct 2009
    Location
    Washington County, OR
    Posts
    3,629

    Default

    I mentioned the backward bearings just to illustrate a possibility. Pages 116-117 of Monroe's How to Rebuild book talks about the various ways to get them installed wrong. Matching holes, block versus cap, aligning grooves, etc.

    Sounds like one of those really difficult problems to solve. If you have an extra assembled short block, you could compare flow rates through the passages by filling with a funnel and watching the drain rate, while blocking passages. Or something similar, I'm not even sure where you would start.

    Even though you don't have signs of a spun bearing you might look for signs of heat buildup from lack of oil. Discoloration.
    Last edited by Zed Head; 09-01-2014 at 11:39 AM.
    1976 280Z, with some minor modifications

  24. #24
    Supporting Member Diseazd's Avatar
    Member ID
    CZCC-14126
    Join Date
    Mar 2007
    Location
    Richmond
    Posts
    1,852

    Default

    If you put your cap bearings on the block side, you'd have known it within minutes of fire up. That's not the problem. IMO
    Last edited by Diseazd; 09-01-2014 at 11:41 AM.
    http://www.flickr.com/photos/1404980...7600346077563/
    ______________________________________________
    http://www.flickr.com/photos/1404980...7603350695459/

    70, 71, 2 72's, and a 73 240z....
    90 300zx and a 1996 Acura NSX.....but who's counting?

  25. #25
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    This will be a bit of a witch hunt. Maybe I will get lucky and something will just fall out in my hand, but I doubt it. It's been like this for literally years .
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  26. #26
    Boat Anchor Repairman Captain Obvious's Avatar
    Member ID
    CZCC-24608
    Join Date
    Jul 2011
    Location
    Philadelphia, PA
    Posts
    1,845

    Default

    Quote Originally Posted by Diseazd View Post
    If you put your cap bearings on the block side, you'd have known it within minutes of fire up.
    That's what I figured as well.

    And I don't think you can put them on and end up with partial covering, can you? I think if you get them on wrong, you completely occlude the oil feed hole. I haven't been in there in many moons however, so memory is quite fuzzy.

    Well good luck with the investigation and keep us posted! It's just so odd to be on the other side of the fence. You so often hear people complain about low oil pressure. How often do you hear the opposite!

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Fuel Pressure - Schrader valves for checking and pressure relief
    By Zed Head in forum Fuel Injection (S30)
    Replies: 4
    Last Post: 08-29-2011, 08:50 AM
  2. Oil pump pressure / pressure regulator
    By bobs77 in forum Engine and Drivetrain (S30)
    Replies: 0
    Last Post: 09-17-2007, 05:00 PM
  3. Low Oil Pressure
    By biker in forum Engine and Drivetrain (S30)
    Replies: 7
    Last Post: 06-16-2005, 06:39 AM
  4. Pressure
    By suleymantezgul in forum Engine and Drivetrain (S30)
    Replies: 0
    Last Post: 08-01-2004, 06:10 AM
  5. oil pressure
    By Bpaccaud in forum Help Me !!
    Replies: 0
    Last Post: 08-07-2003, 04:28 AM

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •