madkaw Posted February 8, 2012 Share Posted February 8, 2012 My oil pressure is almost running a constant 70lbs at all times. I plan on running a mechanical guage in parallel shortly, but I believe the guage is fairly accurate-why do I think that... I am on my second rear main seal- and it leaks. I thought for sure the first one was bad, but now I don't think it is the seal. I have read posts about a plugged PCV system will pressurize the system and cause a leak, but I have checked and rechecked that system and replaced the pcv valve. I am running a high volume pump and was running a HP spring. I replaced the HP spring with a regular pump spring a noticed NO difference in pressure. When I had the head off to replace the HG I blew air through the oil passage of the block to the filter and from the pump to the filter and it seemed to flow freely. This engine is fresh with less than 10k miles. I am running a drilled Schneider cam with NO spray bar. I have looked at the FSM and tried to follow the path of oil, but not sure if this told me anything. I am curious about the relief valve that is in the block. The FSM doesn't give any info about this, but it illustrates it in the flow chart. I believe I have a partial blockage and it is driving up my pressure, but not sure about how to find it.The engine runs good and can't see any signs that any component is lacking oil, but don't want to wait for this to manifest itself into a failure. I appreciate any suggestions to help troubleshoot this item. I am going to get the necessary parts to run the mechanical guage in the next few days, so i will report back on those findings. Quote Link to comment Share on other sites More sharing options...
morbias Posted February 10, 2012 Share Posted February 10, 2012 What weight oil are you running? Quote Link to comment Share on other sites More sharing options...
beermanpete Posted February 11, 2012 Share Posted February 11, 2012 The relief valve is the filter bypass. It will not have any effect on the system pressure. Did you get the mechanical gauge connected yet? I looked at the rear main bearing cap on a spare engine we have . The oil return from the seal side has a slot about 1/8" wide and 1-1/2" long to flow the oil to flow through to return to the sump. I doubt this would restrict the oil flow enough to build any pressure on the seal itself. When the seal failed did it actually pop out? A few possibilities: The sealing surface of the crankshaft could be worn. If there is a groove worn into the shaft it will shorten seal life. A burr on the crank could be cutting the seal as you install it. There are other possible leak paths at the rear of the engine. The rear main bearing cap has a seal on each side. Sealant is required in the corners of the shoulders where the main bear cap fits into the block. The factory service manual shows this on page EM-25 (1973 manual). The oil pan gasket. Quote Link to comment Share on other sites More sharing options...
madkaw Posted February 11, 2012 Author Share Posted February 11, 2012 (edited) Beermate, Thanks for the info on the rear main return. I finally got the fittings to run a mechanical gauge in parallel with my sending unit. The seal is still there, just not holding the oil back.. It leaves a puddle in the garage floor and it comes out the bottom of the bell housing. When I replaced the previous seal it looked as if the oil was coming from the seal area. Everything else was changed too! Haven't run the car yet with the mechanical guage I am going to have a Speedi Sleeve ready to put on if and when I change out the seal So if the rear main cap was removed I would see this slot for the oil return in the cap itself? The filter bypass wouldn't cause high pressure, but what about the pump relief valve. Edited February 11, 2012 by madkaw Quote Link to comment Share on other sites More sharing options...
beermanpete Posted February 11, 2012 Share Posted February 11, 2012 Beermate, Thanks for the info on the rear main return. I finally got the fittings to run a mechanical gauge in parallel with my sending unit. The seal is still there, just not holding the oil back.. It leaves a puddle in the garage floor and it comes out the bottom of the bell housing. When I replaced the previous seal it looked as if the oil was coming from the seal area. Everything else was changed too! Haven't run the car yet with the mechanical guage I am going to have a Speedi Sleeve ready to put on if and when I change out the seal So if the rear main cap was removed I would see this slot for the oil return in the cap itself? The filter bypass wouldn't cause high pressure, but what about the pump relief valve. The oil pressure is generated by the pump not the relief valve. The pump relief valve only determines the maximum pressure. The valve is normally closed and does nothing. When (if) the oil pressure rises to the valve's operating point the valve opens to prevent any rise in pressrue beyond this point. When you get the mechanical pressure gauge installed watch the oil pressure as you rev the engine. It should rise somewhat linearly with engine speed until the bypass valve opens. Increasing the engine speed beyond this point should not increase the oil pressure. When the engine (oil) is cold the oil pressure will be higher at idle than when the oil is hot. If you are using heavy oil (i.e. 20W-50) the oil pressure will be higher than with light oil (i.e. 5W-30) at low engine speeds. Regardless of oil viscosity, temperature, or engine speed the pressure should never be higher than the operating point of the releif valve. Here are a few picuters of the rear main bearing cap and crankshaft. You can see the somewhat crescent shaped slot where the oil returns back to the sump. Note the wear on the crackshaft where the seal runs. The Speedi Sleeve should take care of this type of problem. Quote Link to comment Share on other sites More sharing options...
madkaw Posted February 12, 2012 Author Share Posted February 12, 2012 Excellent pics! This really helps me visually. So if there was something blocking that drain in the main, then it could possibly raise pressure and cause the leak at the same time.(just brainstorming here). I will keep you updated. Quote Link to comment Share on other sites More sharing options...
Tony D Posted February 12, 2012 Share Posted February 12, 2012 Bearings which were incorrectly installed or checked (oiling holes in the bearing partially obstructing the oil feed holes in the block, main saddles, etc...) can cause 'high' oil pressure. I would disagree the oil pressure relief valve is designed to be closed. On the contrary - it is designed to be OPEN to REGULATE the oil pressure in the gallery. The oil pump should be designed to overflow the engine with oil by some margin, and the relief valve is the mechanism by which bearing and internal part wear is automatically compensated for over the normal lifetime of the engine. You may have 30psi at idle and 70 at 2400rpms when the engine is new, and oil at operating temperature...but at 275,000 miles you only have 5psi at idle but STILL have 70 at 2400 rpms. Bearing wear has come to the point that at idle speed the entire capacity of the pump is needed to maintain 5psi on the gallery (and the relief valve then is fully closed, as opposed to being incrementally open at hot idle when new), and of course both instances the relief valve is open and bypassing excess flow at 2400 to keep the gallery at 70psi. Another thing that may be happening is that the pump has sufficient volume at idle that even with the relief valve fully open the orifice dunmping excess oil may be insufficient to relieve the pressure and as a result you have 70psi. Generally if this was the case, though, would be that as RPM rose the oil pressure would rise linearly at the same time. Running straight weight 30 in the winter (say 40F) and 40 in the summer (at 80F) returns consistent results. Multi-Vis will skew the 'cold' readings. If you want to diagnose the problem from an Hydraulic Perspective consider running straight weight to see the TRUE difference between 'cold' and 'hot' oil pressures. It reacts in traditional ways when heated. Some synthetics can have inverse viscosity engineered into them, and it can be thicker hot than it is cold making for strange oil pressure readings. I worked for a German Compressor Company who's relief valve system would give expected results when run on mineral oil, but when run with most synthetics it would have low oil pressure when cold, and higher pressure when hot! And when you put a 'stiffer' spring in the relief valve the pressure in the gallery would DROP! After that, they went to a standard specified oil for troubleshooting. Regardless of what the customer had in there, they would insist any oil related issues be diagnosed with the specified oil. Many times the 'standard' oil revealed exactly what was engineered to happen in the oil system, and deviation from the standard oils (synthetics, multi-vis, etc) would result 'at the customer's peril'! In the L-Engine with as much wear as is on most of the bottom ends tested, they may indeed be 'closed' by now, but when new bearings, new pump and new oil is present - even at idle the relief valve will be incrementally opened (the amount is determined by how much oversized the pump was designed to be) to regulate pressure. After idle, the relief valve has additional capacity to dump overboard by opening further to a point when the overboard dump will not allow any more pressure to dump at which point the pressure will again start to rise. We all probably have seen the engine where it shows "no" oil pressure at idle (5psi) 70psi at most midrange speeds, but the occasional zing to 7000 will result in 90-120+psi oil pressure. That is the phenomenon at work. First thing to do is get a real pressure gauge on there with sufficient range to check and go from there. Quote Link to comment Share on other sites More sharing options...
madkaw Posted February 12, 2012 Author Share Posted February 12, 2012 Well wouldn't you know it -the old Datsun guage is fairly accurate! It is slow to react to changes, but at cruise and idle it is fairly close. The slow reaction of the guage is probably why I summized the higher pressure at idle. It takes about a minute for the guage to stablilize at idle. Warm idle(800rpm), 10w40 on a 30 degree day here= 25lbs pressure(stock guage and verified by mechanical) Driving around it seems to hover around the 70lb mark.(stock guage) The mechanical guage is mounted on top of the valve cover right now, so i can't see it while driving. I will have to figure a way to mount it outside the hood tomorrow. So 70lbs would be normal over what rpms? Quote Link to comment Share on other sites More sharing options...
BLOZ UP Posted February 12, 2012 Share Posted February 12, 2012 Isn't the rear main just at crankcase pressure? Why would high oil pressure cause the rear main to leak? Quote Link to comment Share on other sites More sharing options...
beermanpete Posted February 13, 2012 Share Posted February 13, 2012 Well wouldn't you know it -the old Datsun guage is fairly accurate! It is slow to react to changes, but at cruise and idle it is fairly close. The slow reaction of the guage is probably why I summized the higher pressure at idle. It takes about a minute for the guage to stablilize at idle. Warm idle(800rpm), 10w40 on a 30 degree day here= 25lbs pressure(stock guage and verified by mechanical) Driving around it seems to hover around the 70lb mark.(stock guage) The mechanical guage is mounted on top of the valve cover right now, so i can't see it while driving. I will have to figure a way to mount it outside the hood tomorrow. So 70lbs would be normal over what rpms? My experience of the factory gauge is about the same. The accuracy is ok but the response time is very slow. Your high volume pump is making more pressure at idle than the stock pump does in our car. I suspect you will have 70 pounds by about 2200 RPM or so. It seems the oil pressure is ok. I doubt your oil leak is being cause by too much oil pressure. Quote Link to comment Share on other sites More sharing options...
Lazeum Posted February 13, 2012 Share Posted February 13, 2012 (edited) Isn't the rear main just at crankcase pressure? Why would high oil pressure cause the rear main to leak? I agree with you. Rear main seal is at crankcase pressure. It has nothing to do with oil pressure in the system to me. I would open the breather tube to make sure crankcase is at Atm pressure and see if it is still leaking during a trial. It looks like damaged seal, groove presence in the crankshaft journal or bad seals in the crankshaft cap (the straight units or lack of silicone paste in corners of the cap). If it is a groove in the journal, next time you install a seal, don't push it all the way to avoid having the seal lip right in front of the groove, that should fix the issue. Edited February 13, 2012 by Lazeum Quote Link to comment Share on other sites More sharing options...
madkaw Posted February 14, 2012 Author Share Posted February 14, 2012 Thanks for the input guys, looks like I just need to suck it up and replace the rear main seal again-DAMN IT! I think part of the problem with the last time I did it was that it was hard to see what I was doing. I couldn't get the car jacked high enough to pull the tranny completely out of the way. I believe I scared up the crank pulling the old BAD seal out. I wouldn't have been able to see if there was a groove or bad spot on the sealing surface because of the awkward position I was working with. I think this time I am going to pull the motor instead. It's a little more work, but I want to do this right this time. I will have a speedi sleeve ready to install. Hell, i will probably just redo everything, oil pan and side seals-I hate oil leaks! Quote Link to comment Share on other sites More sharing options...
BLOZ UP Posted February 14, 2012 Share Posted February 14, 2012 (edited) I always pry on the housing of whatever it is. I figure that, a) it's not rotating, and it's wide enough to be able to have a nick on the outside. c) since it doesn't rotate, I can slap some silicone on it if there is a nick. So far so good. Most of the time I just use a small angled pick to go through the lip of the seal (around the crank/cam/whatever rotating part), grab the metal part from behind and yank it out. Edited February 14, 2012 by BLOZ UP Quote Link to comment Share on other sites More sharing options...
madkaw Posted February 14, 2012 Author Share Posted February 14, 2012 Anyone have a crank available in front of them to measure for a speedi sleeve? I imagine all the cranks are the same since all the seals are interchangable. I would like to have this preordered before I pull my engine and want to see if speedi sleeve has the correct size for our application. Quote Link to comment Share on other sites More sharing options...
madkaw Posted April 24, 2013 Author Share Posted April 24, 2013 Well guys, still fighting oil leaks and high oil pressure. Since this posting I have replaced rear main seal again, but first installed a speedi sleeve incase of any nicks on the crank. I have also redid the oil pan and side seals. I really took my time with the side seals considering this might be my issue. I wasn't able to pull the bearing cap out, but I feel competant that I got the seal channels really clean for the new seals. I also mounted the mechanical guage in the car, and the oil pressure rides 70psi most of the time. 2500 rpm cruise and I'm running 70psi. I am running a stock oil pump. So from the above postings, you guys are saying that no amount of oil pressure should cause a rear main leak? Something I am curious about, but might or might have anything to do with the higher pressure. I'm running the early e-88 head that was meant for a spray bar system.I have the block off plates on the cam towers. I am running an eternally oiled cam. Are the oil passages all the same on the cam towers as far as size? I know most guys stick with the spray bars for their regrinds. Might be grasping here, but since there a difference between the oiling holes for the spray bar(small .049 approx.) vs. internally oiled holes in the lobes are bigger(.078)--would there be a difference in the tower oil passages. Again, I know I'm grasping here, but want to cover everything. Quote Link to comment Share on other sites More sharing options...
Tony D Posted September 9, 2013 Share Posted September 9, 2013 Your oil pressure is normal, it is NOT excessive. Quote Link to comment Share on other sites More sharing options...
madkaw Posted July 19, 2015 Author Share Posted July 19, 2015 Just rebuilt my L24. Different block, same head and accessories - oil pressure reads normal. I'm guessing I had a partial blockage in the block or head that drove up the pressure. Idles around 10psi and follows rpms. Quote Link to comment Share on other sites More sharing options...
djwarner Posted July 19, 2015 Share Posted July 19, 2015 (edited) Glad to hear you have your engine running, sounds like a beast. I've got 1600 miles on the cam you sent and it has not missed a beat. Edited July 19, 2015 by djwarner Quote Link to comment Share on other sites More sharing options...
madkaw Posted July 19, 2015 Author Share Posted July 19, 2015 Glad to hear Quote Link to comment Share on other sites More sharing options...
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